1. SOAPS
TECHNOLOGY OF SOAP MAKING
HISTORICAL
SOAP BOILING
Equipment for Soap Boiling
Selection of Fat Charge
The Saponification Reaction
Physical Chemistry of the Soap Kettle
Graining Out and Washing
Strong Change
Finishing or Fitting Operation
Countercurrent Washing
Soap from Fatty Acids
Miscellaneous
SEMIBOILED AND COLD PROCESSES
Semiboiled Soaps
Cold-Made Soaps
CONTINUOUS SAPONIFICATION
Mills Process
Sharples Process
The De Laval Process
The Monsavon Process
Lye Absorption
Saponification Loop
Saponification of Distilled Fatty Acids
Alfa Laval Continuous Saponification
WASHING OF SAPONIFIED SOAP
PLANT FOR TOTAL SOAPMAKING OPERATION
CONSTRUCTION MATERIALS FOR SOAPMAKING PLANTS
Earth Bleaching of oils
Chemical Bleaching
Fatty Acids
Lye Treatment
Storage of Raw Lye
OUTPUT OF SOAP AND GLYCERINE
Analysis of Oils
Ester Value of Oils
FATTY ACIDS
Manufacture from Glycerides
SOAP-MAKING WITH FATTY ACIDS
Tall Oil
Whole Tall Oil
Tall Oil Refining
Tall Oil Soaps
GLYCERIN
Crude Glycerin
Purification
Synthetic Glycerin
CLASSIFICATION OF SOAP PRODUCTS
Spray Drying
MANUFACTURE OF FRAMED SOAPS
MANUFACTURE OF CHIPS AND FLAKES
MANUFACTURE OF MILLED BARS
THE MAZZONI PROCESS
FLOATING SOAP BARS
Mixing of Soap
Preservatives
Perfumes
Colours
Opacifiers
Optical Brighteners
Superfatting Agent
Structurants
Bactericides and Germicides
Miscellaneous Additives
Soapmaking
Fat Charge Control
Colour of Soap Base
Free Alkali and Chloride
Unsaponified Fat
Glycerol in Soap
METHODS OF ANALYSIS
Sampling
Procedures
Separation
Identification
DETERMINATION OF SOAP COMPOSITION
DETERMINATION OF INORGANIC FILLERS AND SOAP BUILDERS
DETERMINATION OF OTHER ADDITIVES
DETERMINATION OF IMPURITIES
OTHER QUALITY CONTROL TESTS
ANALYSIS OF SOAPS CONTAINING SYNTHETIC DETERGENTS
ANALYSIS OF METALLIC SOAPS
SOAP AND OTHER SURFACE-ACTIVE AGENTS
Theory of Surface Action
Quantitative Relationships
Defoaming
Emulsification
Wetting of Solids
Miscellaneous Effects of Adsorption on Solid Surfaces
Detergency
PHYSICAL CHEMISTRY OF SOAPS AND RELATED MATERIALS
Phase Behaviour of Aqueous Systems
Phase Behaviour of Solid Soaps
Nature of Dilute Solutions
Structure of Micelles and Solubilization
Surface and Interfacial Tensions
COMMERCIAL SOAP PRODUCTS
Raw Materials
Production and Consumption
Characteristics of Soaps Saponified by Different Methods
Effect of Different Factors on Physical Characteristics of Bar Soaps
Types of Commercial Soap
SURFACE-ACTIVE AGENTS OTHER THAN SOAP
Classification of Surfactants
List of Surfactants
Production and Consumption
Ampholytic Surfactants
Detergents
Wetting Agents
Emulsifying Agents
2. DETERGENTS
PRODUCTION OF DETERGENT ACTIVE
Introduction
Choice of Alkylate
Sulphonation
CHOICE OF SULPHONATION PLANT
SIDE REACTIONS DURING SULPHONATION
SUIPHONATION PRACTICE
SULPHONATION OF ALPHA OLEFIN
NEUTRALISATION/HYDROLYSIS
CHEMITHON TECHNOLOGY
Storage and Handling
DERIVATION OF FATTY ALCOHOLS
General Outline
PROCESS BASED ON NATURAL FATS
PROCESS BASED ON ETHYLENE SOURCE
SULPHATION OF FATTY ALCOHOLS
CONTINUOUS PROCESS FOR FATTY ALCOHOL SULPHATES
PREPARATION OF DETERGENT GRANULES AS FINISHED PRODUCT
PROCEDURE
Acid Slurry
Alkali Solution
ADDITIVES TO DETERGENT ACTIVES
Inorganic Additives
Phosphates
Zeolites
Silicates
Carbonates
Bleaches
Other inorganic builders and fillers
Organic Additives
Anti-redeposition agents
Optical brighteners (OB)
Foam boosters
Enzymes
Chelating agents
Hydrotopes
Bacteriostats
MANUFACTURE OF SYNTHETIC DETERGENT POWDER
BY SPRAY DRYING
Outline of the Spray Drying Process
Slurry Preparation
Kinetics of Hydration of STPP
Dosing of Ingredients
Slurry Handling
Spray Drying
PRODUCTION OF DETERGENT POWDER BY DRY MIXING
Dry-Mixing Process
Machine-Mixing
Formulations
Compact Detergents
METHODS OF ANALYSIS
Sampling
Separation
Procedure
IDENTIFICATION OF COMPONENTS
DETERMINATION OF SURFACTANTS
Total Organic Active Ingredient
Anionic Detergents
Cationic Detergents
Nonionic Detergents
DETERMINATION OF COMPONENTS OTHER THAN SURFACTANTS
Abrasives
Ammonia
Carbonates
Carboxymethylcellulose
Chlorides and Available Chlorine
Enzymes
Ethanol and Isopropyl Alcohol
Ethylenediaminetetraacetate
Fatty Acids
Glycerine
Hydrotropes
Metallic Impurities
Neutral Oil (Free Oil) and Free Fatty Alcohol
Perborates
Phosphates
Silicates
Steam-Distillable Maller
Sulfates
Water
DETERMINATION OF PROPERTIES
Performance Tests
3. CHEMICALS USED IN SOAPS & DETERGENTS
ALKYLOLAMIDES
Introduction
Alkylolamides in Shampoo Formulations
CHEMISTRY OF THE ALKYLOLAMIDES
Mono-alkylolamides
Di-alkylolamides
Pure Di-alkylolamides
Phosphoxylated Alkylolamides
Sulphated Alkylolamides
FOAM STABILIZATION
MANUFACTURE OF ALKYLOLAMIDES
Coconut Fatty Acid Diethanolamide
Lauric Acid Diethanolamide
Oleic Acid MonoethanoIamide
Stearic Acid Monoethanolamide
FORMULATION OF SHAMPOOS
N-ACYL-N-ALKYLTAURATES
Introduction
Applications of Igepon T Products
Future of Igepons
MANUFACTURE OF IGEPON T
Raw Materials
Oleic Acid Chloride
Igepon T Gel
Igepon T Powder
Chemical Control
Utilities
Materials of Construction
ALKYL SULFATES
Introduction
Manufacture of Alcohols
PROPERTIES AND PERFORMANCE CHARACTERISTICS OF ALKYL SULFATES
Krafft Point
Critical Micelle Concentration
Surface and Interfacial Tensions
Wetting Time
Foam Height
Detergency
Dishwashing Test
Emulsion Stability
MANUFACTURE OF ALKYL SULFATES
Sulfation with Chlorosulfonic Acid
Sulfation with Sulfuric Acid
Sulfation with Sulfur Trioxide
Manufacture of Alkyl Sulfated on Large Scale
FORMULATED PRODUCTS FROM ALKYL SULFATES
OLEFIN SULFATE & SULFONATES
Introduction
OLEFIN SULFATES
Introduction
RAW MATERIALS AND PRODUCT COMPOSITION
Olefin Sulfates from Shale Oil
OLEFIN SULFATE FROM WAX-CRACKED DISTILLATES
Sulfation
Neutralization and Hydrolysis
Evaporation
Finishing
Solvent Recovery
OLEFIN SULFONATES
Introduction
Products of Sulfonation
MANUFACTURE OF OLEFIN SULFONATES
Introduction
Batch Sulfonation
Cotinuous Sulfonation
Sulfonation with Dioxane-SO3
CHARACTERISTICS & SURFACE ACTIVE PROPERTIES OF OLEFIN SULFONATES
FORMULATION OF HEAVY-DUTY DETERGENTS WITH OLEFIN SULFONATES
ETHOXYLATION PROCESSES
Introduction
ETHOXYLATED ALKYL PHENOLS
Laboratory Method of Preparation
Batch Ethoxylation Unit
Properties of Ethoxylated Alkyl Phenols
ETHOXYLATED FATTY ALCOHOLS
Introduction
Laboratory Method of Preparation
Continuous Ethoxylation Unit
Properties of Ethoxylated Fatty Alcohols
Solubility
Cloud point
Surface and interfacial tension
Detergency
Wetting properties
Foaming properties
Emulsifying properties
ETHOXYLATED FATTY ACIDS
Introduction
Manufacture
Properties of Fatty Acid Ethoxylates
ETHOXYLATED FATTY AMINES
FORMULATIONS
ALKYL PHENOL ETHER SULFATES
Introduction
Sulfation and Sulfonation
MANUFACTURE OF ALKYL PHENOL ETHER SULFATES
Sulfamation
Nonylphenol 4-ethoxy Sulfate
Di-(isohexyl/isoheptyl) Phenol Ether Sulfate
Dodecylphenol Ether Sulfate
Sulfation with Sulfur Trioxide
Comparison of Sulfation with Sulfur Trioxide and Sulfamic Acid
PROPERTIES-AND PERFORMANCE CHARACTERISTICS OF ALKYL PHENOL ETHER SULFATES
ALKYL ETHER SULFATES
Introduction
PROPERTIES & PERFORMANCE CHARACTERISTICS OF ALKYL ETHER SULFATES
Individual Alkyl Ether Sulfates
Tallow Alcohol Ether Sulfates
MANUFACTURE OF ALKYL ETHER SULFATES
Process Development
MANUFACTURE OF ALCOHOL ETHER SULFATES
FORMULATED PRODUCTS FROM ALKYL ETHER SULFATES
FATTY AMINE OXIDES
lntroduction
MANUFACTURE OF FATTY AMINE OXIDES
Routes to Fatty Amines
Amine Oxidation
Commercial Synthesis
PROPERTIES AND ANALYSIS OF FATTY AMINE OXIDES
Amine Oxide Properties
Analytical Methods
FORMULATIONS AND USE OF FATTY AMINE OXIDES
Light-duty Liquids
Heavyduty Formulations
BISQUATERNERY AND OTHER CATIONIC SOFTENERS
Introduction
PREPARATION OF BISQUATERNERIES
PERFORMANCE EVALUATION OF SOFTENERS
Multiwash Softeners Evaluation
Softness Evaluation
Rewettability Measurements
PERFORMANCE CHARACTERISTICS OF BISQUATERNERIES AND OTHER CATIONICS AS SOFTENERS
Softener Concentration
Fabric Rewettability Measurements
OTHER MISCELLANEOUS SURFACTANTS
Alkyl Naphthalene Sulfonates
lntroduction
General Method of Manufacture
Nekal ‘BXG’
Nekal ‘BX’ Extra Strong
Dibutyl Naphthalene Sulfonate
Diamyl Naphthalene Sulfonate
SULFATED ALKYLOLAMIDES
Introduction
Igepon ‘B’ Paste
Igepon ‘C’ Paste
SODIUM B-SULFOETHYL ESTERS OF FATTY ACIDS
Introduction
Manufacture of Igepon A
POLYETHYLENE GLYCOL FATTY ACID ESTERS
Intorduction
Manufacturing Process
Fatty Acid Esters of Sucrose
N-ACYLSARCOSINATES
Introduction
Manufacture of Sodium N-oleoylsarcosinate
SULFATED MONOGLYCERIDES
Introduction
Manufacrure
4. BLEACHING AGENTS
History
Mechanism of Bleaching
Bleaching Strength
Methods of Analysis
Identification
ASSAY METHODS
Chlorine-Containing Bleaches
Procedure
Oxygen-Containing Bleaches
DETERMINATION OF IMPURITIES
Methods of Evaluation
BLEACHED TEXTILE PRODUCTS
BLEACHED PULP AND PAPER
Handsheets for Testing of Pulp
Physical Testing of Pulp Handsheets
Brightness of Pulp
Brightness Reversion
Disperse Viscosity of Pulp
Physical Testing of Paper and Paperboard
5. DRY CLEANING AGENTS
STODDARD SOLVENT
Specification Tests
PERCHLOROETHYLENE
Specification Tests
FLUOROCARBON SOLVENT
DRYCLEANING DETERGENTS
Methods of Analysis
Specification Tests
Procedure
PERFORMANCE TESTS
CHEMICAL FABRIC FINISHES
6. DISINFECTANTS AND ANTISEPTICS
GENERAL EVALUATION METHODS
ALCOHOLS
PHENOLS
Methods of Analysis
Separation and identification
Procedure
DETERMINATION IN MIXTURES
BISPHENOLS
Methods of Analysis
Identification
Specification Tests
DETERMINATION IN MIXTURES
SALICYLANILIDES AND CARBANILIDES
Methods of Analysis
HALOGENS AND HALOGEN DONORS
Methods of Analysis
QUATERNARY AMMONIUM COMPOUNDS
Method of Analysis
Separation and indentification
ASSAY METHODS
DETERMINATION IN MIXTURES
Colorimetric Methods
Gravimetric Methods
Titrimetric Methods
MERCURIALS
Inorganic Mercurials
Organic Mercurials
Methods of Analysis
DETERMINATION IN MIXTURES
ALDEHYDES
Methods of Analysis
DETERMINATION IN MIXTURES
EPOXIDES
Methods of Analysis
DETERMINATION IN MIXTURES
GUANIDINE DERIVATIVES
Method of Analysis

^ Top

 Soaps

Technology of soap making

It has been said that the amount of soap consumed in a country is a reliable measure of its civilization. There was a time when soap was a luxury now it is a necessity. The current manufacture of vast amounts of soap in every civilized country is possible only because new raw materials have become available through chemical science the tallows and animal greases of the old days have been supplemented by coconut palm cottonseed and other oils. The  old  days are those when soap was practically the only detergent. Today syndets (synthetic detergents) account for more than 70 per cent of all detergents used.

The technology of soap making is involved and practical soap making borders at times on an art due to the extraordinarily complex physical nature of soap and its aqueous systems. After saponification  in itself an exacting operation  the soap must be carried through a series of phase changes for the removal of impurities  the recovery of glycerine  and reduction of the moisture content to a relatively low level.

The complete series of operations in the production of an ordinary full boiled or settled soap is as follows  (a) reaction of the fat with alkali until it is largely saponified  (b) graining out of the soap from solution with salt in two or more stages for recovery of the glycerol produced by the reaction  (c) boiling of the material with an excess of alkali to complete saponification  followed by graining out with alkali  and (d) separation of the batch into immiscible phases of neat soap and niger the so called  fitting  operation.

The neat soap   consisting of about 65% real soap with about 35% water  and with traces of glycerine  salt etc.  is the product from which with or without drying  mechanical working  and addition of nonsoap ingredients are formed commercial bars  flakes  granules  and powders  from the kettle soap process.

The following sections describe the operation of soapboiling and recent continuous saponification methods in a general way and are of course not intended to constitute a manual for the operation of difficult soap manufacturing processes.

Historical

Soap is one of the oldest chemical substances known. Its history begins before the earliest written literature. Clay tablets inscribed in Sumerian in about 2500 B.C. record knowledge of a potash soap made from oil and the ash of a plant rich in potassium carbonate and the use of this soap in washing wool. Pliny  however  (A.D. 77)  has attributed the invention of soap to the Gauls  who made it from goat tallow and beachwood ash and used it to dye their hair red.

During the Middle Ages the art of soapmaking survived in certain cities in Italy  France and England. In the eighteenth century it had reached a high state of development in a number of places notably Marseilles which is still an important center. Early soapmakers followed the laborious practice of leaching potassium carbonate from wood ashes causticizing it with slaked lime and using the caustic potash for saponification. For production of hard soaps it was necessary to salt out the resultant soft potash with common salt.

In the nineteenth century following the introduction of the LeBlanc process for caustic soda manufacture soap became much cheaper and its use very common.

Soap Boiling

Equipment for Soap Boiling

The boiling of soap is carried out in large cylindrical kettles with cone bottoms  equipped with open and sometimes with closed coils for steam (in Europe square kettles or  pans  are often used). The kettles are provided with delivery pipes for fat  water  lye  brine  and niger or other soapstocks brought from other parts of the plant. A swinging suction or  skimmer  pipe operated from the top is installed to permit drawing off the contents to any desired level  and in the bottom another line is provided for withdrawing the residue left from skimming. Since contamination of the soap with rust is very undesirable  the steel kettles are clad with nickel or other corrosion resistant metal  at least down to below the usual liquid level.

Soap kettles may be as large as the production of the plant will permit  in larger plants they may have a total water capacity of several hundred thousand pounds and seldom  except in the smallest plants  has this capacity been less than about 150 000 pounds. In order that the soap batch may not cool and become excessively viscous during a prolonged period of settling neat soap from niger  the kettles must not be too small. Further a large batch requires no more of a soapboiler s expert attention than a small one. A typical kettle will have a capacity of about 8000 cubic feet and a water capacity of 500 000 pounds. The batch is often started on the niger from a previous boil the fat charge must not exceed about 25 30% of the water capacity of the kettle and hence a kettle of this size will take about 125 000 pounds of fat plus 50 000 pounds of niger. From this the yield will be about 200 000 pounds of neat soap  plus 50 000 pounds of niger to be used in starting another batch.

Selection of Fat Charge

It will only be repeated here that the principal considerations are the provision of a fat mixture containing saturated and unsaturated  and long  and short chain fatty acids in suitable proportions to yield the desired qualities of stability  hardness  solubility  ease of lathering  etc.  in the finished product  and sufficient refining and bleaching of the fat charge to ensure a good appearance. A very common mixture for the manufacture of toilet soaps is about 75% tallow and 25% coconut oil. To produce a white toilet soap of sufficiently light color. Thomssen and McCutcheon recommend that the color of the tallow be not darker than 3 on the FAC scale  and that the coconut oil have a Lovibond color not in excess of 10 yellow and 2 red.

As a general rule for the selection of a fat charge  the empirical INS method of Webb deserves some mention. The INS factor of a fat is defined as the saponification number minus the iodine number  the INS factor of a mixture of fats is calculated proportionally from the factors of the individual fats. In a mixture the SR factor is calculated by dividing the INS factor as defined above by another similar factor in which the individual INS factors of coconut and palm kernel oil and all liquid oils (with INS less than 130) are taken as zero. For toilet soaps an INS factor of 160 170 and an SR factor of 1.3 1.5 are recommended that commercial soaps behave essentially like salts of single fatty acids  with negligible fractionation of the individual components occurring upon separation of the soap into two phases or partial transformation of the soap from one phase to another.

In the diagram the percent by weight of anhydrous soap is plotted along the vertical axis  and the percent by weight of salt (sodium chloride) is plotted along the horizontal axis. The weight percent of water is  of course  100% minus the combined percentages of water and salt  hence the composition of any combination of soap  water  and salt can be represented by a single point. While only one electrolyte  sodium chloride  has been represented  the effect of mixed electrolytes in such systems is additive  hence the diagram may also be considered to indicate the action of caustic soda or mixtures of caustic soda and salt  calculated in terms of sodium chloride.

Figure 1 shows four one phase regions  A  B  D  and J comprising  respectively  neat soap  middle soap  niger (isotropic solution)  and kettle wax. The horizontal ordinate constitutes an additional single phase region consisting of  lye  or soap free electrolyte  but existing here in one dimension only.

There are six two phase regions represented by C E F I  K  and M. In the figure they have a shaded appearance from the tie lines which have been drawn in. When the composition of the system is brought into one of these regions  the composition of each phase separating will be represented by the ends of the tie line passing through that particular composition. Also  the amounts of each phase produced can be calculated from lengths measured on the tie line according to the so called  lever principle.  Thus  for example  if the system is brought to the composition represented by y  so that separation occurs into kettle wax and lye  the composition of these two phases will be represented by y  and y   respectively. The fraction of kettle was will then be equal to yy /y y   and the fraction of lye will be equal to yy /y y .

Finally  there are three triangular three phase regions G  H and L. In each of these the composition of the three phases separating is the same throughout the region  and is represented by the apexes of the triangle.

The Saponification Reaction

The successive operations performed on a single batch of material in the soap kettle to produce a  settled  soap are termed  changes .

Fats are blended to produce soap with the desired characteristics before they are saponified. Except to a limited degree in certain special products it is not practicable to blend different stocks after saponification  although the so called soap builders and other nonsoap ingredients are mixed in after saponification is completed.

Physical Chemistry of the Soap Kettle

It is necessary here to consider only the system of soap  water  and electrolyte existing at approximately 100ºC  in a soap kettle. Such a system is represented in part of the diagram of Figure 1. In the present discussion this diagram is intended to be illustrative only  although the phase boundaries have been placed reasonably close to those actually reported for representative commercial soaps. The various operations in soapboiling can be explained with reference to this diagram. The work of McBain  Ferguson  and others has shown.

The first of these  designed to effect saponification of the greater part of the fresh fat  is often called the  killing change.  It is carried out by boiling the fat and alkali together with open steam. Since neutral fat and aqueous alkali are immiscible  the reaction rate is at first slow and principally dependent upon the magnitude of the interface between the two liquids. In the later stages  however  saponification may be considered an essentially homogeneous reaction  proceeding through concurrent solution of fat and alkali in a phase consisting of performed soap. The reaction is therefore markedly autocatalytic. If the amount of fat saponified is plotted against reaction time  a sigmoid curve results  the reaction  at first slow  accelerates rapidly as increased quantities of soap are formed  and slows again only toward the end as the concentration of fat becomes low and considerable proportions of fat tend to become occluded among alkali improverished soap micelles. The marked ability of strong soap solutions to dissolve neutral fats and the significance of this phenomenon in soapmaking was perhaps first pointed out by Smith  is now generally recognized  and is in fact an important principal of the De Laval continuous saponification process.

In technical practice  soap is often boiled on a niger of preformed soap left from a previous boil. Fresh fat and alkali slowly added to the boiling soap mass saponify very rapidly. Considerable heat (about 65 cal./kg. of fat saponified) is evolved in the reaction  however  and the addition of fat and lye must be carefully controlled to avoid boiling the batch out of the kettle from the excessively rapid generation of heat.

The fresh lye used for the killing change commonly has a strength of about 30ºBé.  corresponding to a sodium hydroxide content of 23.5%. The amount of such lye required for complete saponification is in the range of 60 65 pounds per 100 pounds of fat for most stocks. The use of so called  half spent  lyes  the condensation of steam  and the practice of boiling upon a previous niger  however  increase the minimum weight ratio of soap to lye  and at the end of the saponification step the soap content of the kettle is usually in the neighbourhood of 50%.

During the boiling operation it is necessary to keep the composition of the batch reasonably well within the portion of the diagram comprising areas F  H  and I (Figure 1). This can be done only by maintaining an excess of alkali during the first part of the operation and adding salt or strong brine to increase the electrolyte concentration  as the alkali decreases toward the end of the reaction. If the composition is allowed to come within area B  C  E or G  thickening or  bunching  will occur from the formation of middle soap. This phase appears in the form of very viscous  gummy lumps that are difficult to eliminate once they are produced in quantity. Middle soap may be formed locally if the batch is not boiled vigorously  even if the total composition of the batch is correct. On the other hand  if the composition is allowed to enter areas L or M  through alkali being present in too great excess   curd  soap will separate and retard saponification  as this soap is a poorer reaction medium than neat soap. Neat is also a better medium for reaction than is niger  hence it is desirable to keep the batch just barely  closed  or liquid  at a composition  for example  represented by x in Figure 1. The condition of the batch throughout the operation is judged by the soapboiler almost entirely accordingly to its appearance in the kettle  or as withdrawn in small portions on a trowel  and according to the degree to which excess alkalinity produces a  bite  on the tongue. Phenolphthalein or other indicator may be used as an auxiliary guide to the progress of the reaction.

Since the lye  or soap free liquor produced by the killing change  is processed directly for glycerine recovery  it is customary to finish this change with a virtually neutral lye and an excess of unsaponified fat (usually about 2 10% of the original amount) remaining. Saponification of the fat is completed in a subsequent operation.

The saponification rate is greatly increased by the presence of about 1% of certain phenols  cresols and b naphthol. These are particularly effective for oils of relatively high unsaturation and have been used to some extent by European soapmakers  but it is not in the United States.

Graining Out and Washing

Following saponification the soap is grained out by the addition of salt to the boiling mass. Practice varies in the use of salt  some operators use dry salt  which is sprinkled over the surface of the kettle  while other prefers to use strong brine. If brine is used  more water must be evaporated in the subsequent recovery of glycerine but  on the other hand  it is more easily handled than dry salt.

The object of graining out is to bring the system into region  M (Figure 1)  so that the soap may be separated from the  spent  glycerine containing lye. The soap rises to the top of the kettle in the form of rough masses commonly referred to as  curd  or  kettle wax.  This form  of waxy texture at soapboiling temperature  is converted to a white solid curd upon cooling. The point y in Figure 1 represents the total composition of a representative batch brought to the point of graining out  with points y  and y  representing the composition of  curd  and lye  respectively.

The greater part of the glycerine is recovered in the liquor drawn off from the first or killing change  in noncounter current operation  the spent lye may contain up to 6 8% glycerine. It is necessary to carry out further brine changes or  washes  to make recovery substantially complete. These are carried out by adding water to the curd mass again to bring the composition of the batch into the closed or liquid region and again graining out as described above. The number of washes given the batch is variable  but is ordinarily not less than two.

Strong Change

Before the soapboiling operation is completed it is necessary to ensure that small proportions of neutral fat left from the killing change are completely saponified. This is accomplished by the so called  strong change   carried out similarly to the washes described above  except that graining out is accomplished with caustic soda rather than with lye  and the batch is given a prolonged boiling. No recovery of glycerine is accomplished in this change  the  half spent  lye resulting from the operation is used for the saponification of fresh batches of fat.

Finishing or Fitting Operation

The final step in soap boiling is the so called  fitting  operation sometimes called  pitching  or  finishing . The finishing change may follow the strong change directly  or another brine change may be interposed if it is desired to make the free alkali content of the finished neat soap very low at some expense of its salt content.

In finishing  the soap is closed by boiling with water as before  and its content of water and electrolyte is so adjusted that the composition of the system is brought into region F (Figure 1)  for example  to the point z. Upon standing the batch will then separate into an upper layer of neat soap and a lower layer of thinner niger. In the example  the composition of these is represented by the points z  and z  respectively. The principal object of the separation is purification of the neat soap  the niger retains most of the dirt  coloring materials  metallic salts  and other undesirable impurities of the batch  as well as much more than its share of dissolved salt or free alkali. It will be seen from the diagram that the portion of the neat soap boundary adjacent to area F is narrow and relatively flat  hence with a given stock the composition of the neat soap can vary only little.

In most commercial soaps the real soap content is in the neighbourhood of 65 66%. On the other hand  the composition of the niger and the relative amounts of neat and niger can vary widely. The fitting operation is highly critical and requires the utmost skill upon the part of the soapboiler. The very narrow limits within which he must work are evident from the diagram. The addition of slightly too large an amount of water or salt will produce too large a niger  and diminish the yield of neat soap. If too little water or salt is added  too small a niger may be produced  and purification may be short of that desired. Furthermore  by the addition of water not greatly in excess of the proper amount  by the use of insufficient salt  or by failure to mix in the water thoroughly as it is added  the batch may be brought into regions G or E  with the formation of lumps of middle soap. Ordinarily  a niger is taken off which amounts to about 20 25% of the kettle contents and which contains about 30 40% soap. Upon settling  the niger layer increases in soap content at the top rather than at the bottom whereas the neat layer remains substantially uniform in composition.

The phase boundaries are considerably altered by changes in the composition of the fat. The comparative phase diagrams of Ferguson and Richardson for tallow soap  coconut oil soap  and mixtures of the two are shown in figures 2 5. The areas of homogeneity and heterogeneity of the different soap phases extend over progressively wider concentrations of electrolyte as the percentage of coconut oil in the fatty stock increases. This effect makes the accidental formation of middle soap more likely in stocks containing large proportions of coconut oil than in ordinary stocks. Considering the necessity for precisely determining the composition of the batch to make the pitching operation successful  and the variability in phase boundaries occasioned by unavoidable variations in the fat  it cannot be readily reduced to a series of mechanical operations  but must depend upon the skill and judgment of the experienced soapmaker who is able to judge the progress of the operation closely by the appearance of the batch.

Countercurrent Washing

Large plants with ample kettle capacity may use the so called countercurrent wash system  to reduce to a minimum the amount of water to be evaporated in the recovery of glycerine. In the operation of this system only the spent lye of high glycerine content produced by the killing change is pumped directly to glycerine recovery  the weaker lyes from succeeding changes are used repeatedly for washing and are pumped from kettle to kettle in such a manner that they pass countercurrent to the soap mass  being progressively enriched in glycerine content in the process. For maximum glycerine strength in the spent lye it is also necessary to incorporate the niger from a previous batch during one of the washes rather than using it to aid saponification of the fresh fat.

The countercurrent system will afford a 95% recovery of the theoretical amount of glycerine available  with a ratio of less than 1 pound of spent lye produced per pound of fat saponified.

Soap from Fatty Acids

There has been considerable manufacture in the kettle of soap from fatty acids. When fatty acids are used as the fat stock saponification may be effected with sodium carbonate and  of course  no glycerine is recovered. A nearly saturated soda ash solution is brought to a boil in the soap kettle and the fatty acids are added gradually  allowing sufficient time between additions for carbon dioxide to escape without the batch foaming over. After neutralization the batch is boiled with an excess of caustic soda  to saponify the small amount of neutral  unsplit fat which may be present in all but the better grades of distilled acids. This treatment corresponds to the  strong change  in ordinary soapboiling and subsequently the batch is finished as described previously.

The neutralization of fatty acids to make soaps in different types of crutchers  kneaders  or dough mixers rather than in the soap kettle has been described by Reinish. Soaps are also made from fatty acids in a continuous process which integrates the initial steps of high pressure fat splitting and fatty acid distillation with subsequent saponification and processing of neat soap.

Among other advantages  greater flexibility in choice of raw materials  in blending  and in formulations makes the fatty acid method particularly  suitable for the production of solid or liquid specialty soaps  paste and cream soaps  waterless hand cleansers and powdered hand soaps. An estimated 25 to 30 million pounds of commercial distilled fatty acids go into specialty soapmaking  quite apart from integrated soapmaking via the fat splitting route.

Miscellaneous

Soapboiling Using Rosin. In the manufacture of yellow laundry soaps  or other soaps containing rosin  the rosin is either saponified separately or added after the glycerol has been removed by the first brine changes. Rosin contributes no glycerol to the spent lyes  and it is considered to  hold up  glycerol  if present in the first stages of saponification.

Time Required for Soapboiling. The total time required for preparing a batch of full boiled soap is usually about 5 10 days  it varies according to the number of changes carried out  the size of the kettle  and whether rosin is included in the formula. In the first changes  about 4 8 hours are usually allowed for boiling and 4 16 hours (over night) for settling. After fitting  the batch is usually settled for not less than 2 days  and in some cases as long as 5 days.

It would obviously be desirable if soapboiling could be conducted with full control of the quantity of materials in the batch  with the success of the operation depending less upon the personal judgment of the soapboiler. Many efforts made to introduce systems of quantitative control have met with success only in the more recent continuous saponification methods.

Wigner in particular  has treated this aspect of soapboiling at length  and has described methods for the control of both washes and fit  using a back pressure  liquid level gage to estimate the weight of the kettle contents. According to Govan  this method of weight estimation is generally accurate to within ± 2%  and could be of real assistance in regulating the size of the washes.

Bleaching in the Kettle. Soap may be bleached with sodium hypochlorite or other chemical agent in the kettle  preferably after the batch has been purified as much as possible by several  washes . Bleaching is carried out after water has been added to the curd to form a solution  and the soap is again grained out after the bleaching is completed.

Purification of Nigers. Impurities in the soap batch in the kettle process tend to accumulate in the niger  which cannot be used indefinitely for addition to fresh batches without purification. Purification of the niger can be accomplished by boiling and either  pitching  or salting out.

Soap Additives. Soap additives for soap in various physical forms  such as bars  granules  chips  flakes  quick dissolving forms  transparent  paste  or liquid soaps made in kettle  and continuous saponification or other methods have been discussed in Chapter 11. Additives include  for example  abrasives  antioxidants  builders  fillers  germicides or deodorants  medicinals  perfumes  sequestrants  soil suspending agents thickeners  optical bleaches dyes  and pigments. The stage in manufacture at which these should be added may depend upon their possible loss or destruction by chemical action or volatility.

Semiboiled and Cold Processes

The semiboiled and cold processes represent soapmaking in its simplest form  the fat is caused to react with a quantity of strong alkali very nearly equal to that just required for complete saponification  and the entire mass is solidified without separation of the free glycerine and without separation of neat and niger phases. These processes have the advantage of requiring simple equipment and comparatively little skill on the part of the soapmaker  and a soap may be produced with an anhydrous soap content of any desired value over a wide range. On the other hand  they do not permit recovery of the relatively valuable glycerine  the raw materials do not under go the purification obtained by the full boiled process  and the product is generally considered somewhat inferior to settled soaps.

The two processes are used for making marine or other coconut oil soaps  which are difficult to handle by the full boiled process  for making soft or potash soaps (which cannot be easily salted out)  and for relatively cheap and heavily filled soaps made in small plants.

Semiboiled Soaps

Semiboiled soaps may be made either in an ordinary soap kettle or in small batches in a crutcher. In either case  the fat charge is simply heated with the requisite amount of strong caustic soda (25 35ºBé.)  and after saponification is completed sodium silicate or other builder or nonsoap ingredient is added. If the operation is carried out in a kettle  the batch may be actually boiled  but if performed in a crutcher the temperature must be kept a little below the boiling point  and mechanical agitation is depended upon to ensure thorough mixing during the reaction. However  to make the finished material homogeneous the kettle batch must be cooled slightly and mixed by recirculation from bottom to top through a pump before it is solidified.

Cold Made Soaps

Insofar as the operation is concerned  the cold process differs little from the semiboiled process as carried out in the crutcher  except in the temperature employed.

Mixing is carried out substantially at room temperature  so that little more than thorough emulsification occurs in the crutcher. Very strong lyes  34 45ºBé.  are employed  the emulsion of strong lye and fat formed in cold saponification is reported to be of the water in oil type  as distinguished from the oil in water type produced in soapboiling. Saponification is completed after the soap is run into frames  several days at a reasonably warm atmospheric temperature are required for completion of the process.

Since there is no opportunity in the manufacture of cold made soaps to adjust the proportions of fat and lye according to the reaction of the two  the charge must be quite carefully calculated. However  these soaps usually contain a substantial excess of either alkali or  more commonly  fat. Any addition of builders  perfumes  or coloring material to cold made or semi boiled soaps must  of course  take place in the crutcher.

Semiboiled and cold made soaps are frequently prepared from fatty acids  as well as from fats.

Continuous Saponification

To avoid the time consuming operations and excessive steam consumption of conventional soapboiling  a number of continuous saponification processes have been devised  and are now being used commercially on a very large scale  and are displacing  the kettle soap process. A brief description of the Mills  Sharples  De Laval and Monsavon processes will illustrate the newer continuous saponification methods and their special advantages.

Mills Process

The first continuous saponification process to be operated on a large scale is that patented by Mills. It involves  as a first step  splitting of the fat stock to produce fatty acids. The acids are then purified by distillation  which takes the place of washing and the separation of neat soap and niger for the removal of color bodies and other impurities. The complete process  as carried out in the soap plant  has been outlined by McBride  from whom the following description is taken.

In small batches the blended fat stock is mixed with a small amount of powdered zinc oxide and held at 220ºF. The zinc oxide  which acts as a catalyst for hydrolysis  is soluble in the somewhat acid fat at this temperature  forming zinc soaps. In a second feed tank water is maintained at 200ºF.

High pressure pumps of the piston type pick up fat and water separately  at controlled rates. Beyond the pumps the two streams  under a pressure of 600 pounds  are heated to 495º and 480ºF.  respectively  by the direct injection of 900 pound steam. The fat is fed at the base and water at the top of a hydrolyzer column  also at 600 pound pressure. This column consists of a 65 foot tower  without packing or baffles  in which most of the splitting takes place. The superheated water falls to the bottom of the tower in countercurrent flow to the hot fatty material  carrying with it the glycerol resulting from splitting. A time of 90 minutes in the apparatus is reported to be sufficient for over 99% splitting. Owing to the great solubility of water (of the order of 12 25%) in fats and fatty acids at the high temperature employed and the relatively slight difference in the density of the water and fat phases  elaborate measures for interdispersion of the two phases at any stage are unnecessary.

The  sweet waters  at the bottom of the tower are released through a pressure regulating valve to a flash chamber and a multiple effect evaporator  where they are concentrated to yield crude glycerine. The water saturated fatty acids at the top of the tower are similarly released to a flash tank  where the temperature is reduced by flashing off the dissolved water. From the flash tank the crude acids pass to a tank which feeds the distillation equipment. In this tank they are protected from the air by a blanket of steam.

Prior to being fed to the still  the fatty acids are heated to about 460ºF  in a Dowtherm heater. Distillation is carried out under a pressure of 2 5 mm. The still may consist of a tray and bubble cap tower down which the crude acids flow  with the unhydrolyzed fat being taken off at the bottom  or of a pot still of special design. In the latter case  a large proportion of the still bottoms is continuously recirculated through the Dowtherm heater to assist in maintaining the temperature in the still  and a minor proportion is continuously withdrawn to maintain the concentration of unsplit material in the still at a fixed level. The still bottoms are reworked in a second processing stage  or may be diverted for use in soap powders or lower grade products.

The construction of the hydrolyzing and distillation equipment is of stabilized stainless steel where high pressures or temperatures are involved  and of aluminum where pressures are low.

The fatty acid distillate  cooled to about 180ºF  is continuously fed together with caustic soda solution with proportioning pumps to a high speed mixer  where saponification takes place almost instantaneously. The strength of the caustic soda is so adjusted that the composition of the product falls in the range of ordinary neat soap  and sufficient salt is added to the caustic soda to give a soap of the customary electrolyte content. Following this operation  the neat soap is processed into various forms in the usual way.

One of the prime advantages of the process involving splitting before saponification is its great flexibility. Stocks difficult or impossible to bleach satisfactorily can be distilled to yield light colored fatty acids  and the manufacturer is not limited to a product having the composition of neat soap but may produce a soap directly of substantially lower moisture content. This may be an advantage since many commercial products (floating soaps  toilet soaps  spray dried products) are marketed with a moisture content lower than that of neat soap. Furthermore  potassium soaps of high purity can be prepared as readily as sodium soaps. The Mills process is reported to produce soap products  including high grade toilet soaps  which are fully equal in quality to those made by the best soapboiling practice. There are complete plants employing the integrated fat splitting process which have no soap kettles.

Sharples Process

The Sharples continuous centrifugal process follows the same path as the traditional kettle process saponification washing  and fitting. However  all steps are accomplished rapidly and continuously by separating soap and lyes and neat soap and niger with the aid of high speed centrifuges. Less than two hours is consumed in converting the fat stock to neat soap  and the steam consumption  amounting to about 0.17 pound per pound of fat processed  is only 15 20% of that in soap kettles. The ratio of spent lye to fat saponified (0.5 0.7 pound to 1 pound) is substantially less than that achieved in the best batch countercurrent washing practice  and only neat soap and spent lye are discharged. The niger may be continuously recycled  but in fact there is no niger in the usual sense since the dirt and coloring matter usually associated with nigers in kettle boiling are accumulated on the inside of the centrifugal bowls and removed periodically.

The neat soap from the Sharples process is bright and clean since the fat is heated only 1 2 minutes before saponification  corrosion resistant materials are used  saponification  is rapid in a closed vessel  and the soap is clarified four times under high centrifugal force. Savings in steam  labor  and maintenance are claimed  and the spent lye contains two to three times as much glycerine as that from the kettle process.

The flow of materials in the Sharples process is illustrated in figure 6  which is largely self explanatory. There are four stages of processing   three stages of saponification and washing  a final stage of fitting. With the use of automatic flow controls and interlocking proportioning pumps  accurate control of the entire process is achieved by periodically checking the caustic content of the lye at a single point in the system. Standard plants have capacities (in terms of fat processed) ranging from 1500 to 13 500 pounds per hour  in multiples of 1500 pounds.

The De Laval Process

The De Laval Centripure process for the continuous saponification of fat is similar to both the Sharples and the Monsavon methods. It is a centrifugal process characterized by a totally enclosed system with automatic control of washing and fitting operations.

In the first section neutral fat fed into preformed soap containing excess caustic is immediately dispersed  dissolved and saponified catalytically at 90 120ºC. Excess lye avoids formation of middle and acid soap as undesirable phases. The soap formed passes to the second section  where it is salted out or washed countercurrently in two stages.

Fresh  concentrated brine is added in the second stage and  after dissolving the glycerine  the brine is separated together with impurities from the neat soap in a high efficiency hermetic centrifugal separator. Spent lye from this stage is returned to the previous stage where  after dissolving more glycerine  it is again separated and is then discharged to the glycerine house  simultaneously removing more impurities.

From the second washing stage the washed neat soap now containing only small amounts of glycerine and impurities is led to a third section.

To obtain high grade toilet soap the  neat soap is fitted in the third section by adding brine and caustic in such amount that the soap divides into two phases  neat soap and niger.

Separation of neat soap and niger is effected in a third separator. The niger is returned to the second washing stage. The soap  now fitted and free from niger  is discharged from the process and then undergoes normal high grade toilet soap treatment  comprising drying  milling  plodding  and stamping. Somewhat different procedures are used to obtain ordinary toilet soap  washing soap  and soap powder.

The De Laval process is characterized by very close automatic control of the washing and fitting operations  based on the fact that soap changes characteristically in viscosity as a function of electrolyte concentration. At low electrolyte concentration soap is very viscous. With increasing electrolyte the viscosity decreases to a minimum and with further increase in electrolyte the viscosity begins to increase again. These changes in viscosity are recognized by instruments and the amount of electrolyte is adjusted automatically in each washing and fitting operation.

The smallest De Laval plant has a capacity of 1000 kilograms of fitted 63% fatty acid content neat soap per hour. Advantages claimed for the process are low steam consumption  savings in space and labor  flexibility and versatility  a high glycerine content in the spent lyes  and the production of soaps of excellent color  improved stability  and optimum homogeneity free from undesired aeration.

Besides the Sharples and De Laval centrifugal methods still another recent one is the Podbielniak or Soaprazon process for continuous soap washing and finishing  using multistage countercurrent centrifugal contactors.

The Monsavon Process

The Monsavon is one of the earliest continuous processes for saponification and washing. It resembles the Sharples process but uses a colloid mill for saponification  and separations are by gravity settling rather than by centrifugation.

Fat at 160ºF. and aqueous sodium hydroxide in 4% excess at room temperature are continuously metered by variable stroke piston pumps into a colliod mill to form an emulsion of aqueous caustic in oil. This intimate contact reduces the induction period for saponification to a very short time. The finely dispersed mixture then flows through a reaction tube without further agitation into a soap kettle where very mild agitation is maintained and saponification is completed in a single stage. The saponification mixture at 200 220ºF.  with all of the heat of reaction conserved  leaves in the neat phase and is pumped from the bottom of the soap kettle to a washing tower which consists of six separate washing sections arranged vertically and thermostatically controlled at 85ºC. The crude neat soap ascends in this tower and is washed countercurrently.

Each section contains a mixing compartment that consists of a cylinder extending across the section  with a simple mixing mechanism which blends soap and lye on a continuous basis. The raw soap enters the first lower section just as the lye required for fitting enters the top of the tower. Niger continuously recycled to the washing tower may be recycled for months without deterioration in the color of the soap. The washed soap rises from the last washing sections in a continuous stream into the fitting section at the top of the tower  where it is continuously mixed with water and brine or caustic soda. Fitted soap is continuously withdrawn to a settling tank. The process is continuously controlled with respect to (a) completeness of saponification through measurement of the turbidity of a 15% soap solution  and (b) free alkali content by photoelectric examination of the finished product to which alcoholic phenolphthalein has been added.

The Monsavon process terminates with excellent quality neat soap of 62 63% fatty acid content in 24 hours. The improvement in quality is obtained by the elimination of injected steam carrying various contaminants  by practically instantaneous separation of soap and lye  and by rapid processing with reduced risk of metal contamination. The process is claimed to save time  space  power  and labor  to avoid the production of nigers (since these are continuously recycled)  and to effect high glycerine recovery. However  very strict automatic control is essential  and the process produces only one kind of soap. Production by this process was estimated at 500 000 tons per year in 1959.

The Monsavon and Unilever processes are quite similar  with the basic difference that in the Unilever a steam jet is used for emulsification rather than a colloid mill.

 

Detergents

Production of Detergent Active

Introduction

The essential ingredient of a detergent is the active matter  which may be of anionic  cationic or non ionic types  the more common ones being anionics and non ionics. These actives may either be purchased from third parties or produced in the detergent manufacturing site itself for captive consumption.

In this chapter  a description of the processes for sulphonation is discussed  taking linear alkyl benzene and alpha olefin as the starting materials. The bulk of the detergent powders found in the market use linear alkyl benzene sulphonate (LABS) as the active ingredient in the formulation.

Choice of Alkylate

Before the advent of linear alkyl benzene (LAB) the chief raw material for the active was dodecyl benzene (DDB) a branched chain alkylate. This alkylate had the following drawbacks

          Increase in viscosity during sulphonation thus necessitating efficient mixing.

          Side reactions affecting yields

          Poor bio degradability

          Generally  dark colour of the sulphonic acid at higher levels of conversion.

On the issue of bio degradability  DDB has been replaced by LAB. In India  LAB is produced as the basic material for the active matter although the performance of DDB sulphonate is marginally superior to LAB sulphonate.

The molecular weight of LAB is usually specified as 240 ± 5 taking into account the optimal carbon distribution and the chain length required to ensure good solubility  foaming property and detergency.

In general  C10 to C14 is the normal range of alkyl chain in alkyl benzene used in synthetic detergents  the bulk of it (97%) being in the range C10 C13 and about 2% being C14 and above.

Some isomerisation takes place during the manufacture of LAB depending on the position of the benzene ring in the paraffin chain. The manufacturing conditions are adjusted so as to produce the right distribution of the isomers for good sulphonatability.

Table 1 gives a typical specification of LAB. It can be seen that the bio degradability of LAB is of a high order  sulphonatability is 98% and the C10 C13 chain accounts for 97.5%.

Table 1

Sulphuric Acid

While using sulphuric acid  the chemical reaction results in the liberation of water. Since water retards the reaction  a large surplus of acid is needed to ensure its completion.

A 1000 kg jacketed stainless steel reaction vessel fitted with a 120 rpm anchor type stirrer may be used for sulphonation. 350 kg alkylate is charged into the vessel at 40° 45°C. The acid is gradually added over a period of 2 3 hrs until the total addition corresponds to approximately 1.6 times the weight of the alkylate. The reaction temperature is regulated at 45°C by controlling the cooling water. During the course of the reaction the colour of the mass changes from colourless to milky white  brownish yellow and then to light brown.

On completion of the acid addition  the mass is kept agitated for approximately three hours  the temperature being maintained at not more than 50ºC. The reaction is complete when the unconverted alkylate content is 15 to 2.0%. An empirical test for conversion is to shake two drops of the reaction mass with 10 cc of 35% (w/v) ethyl alcohol in water. If the conversion is 97 98% the resulting solution will be clear. This method needs to be optimised. The reaction mass is transferred to a settler for separation of excess sulphuric acid. Separation is normally carried out in a lead lined jacketed mild steel conical bottomed vessel  fitted with an agitator (with a speed of 120 rpm). The sulphonated mass is transferred into this vessel and crushed ice or chilled water at 8 10°C is added within 2 2½ hrs. taking care to see that the temperature does not exceed 65°C. The quantity of water / ice added is approximately 10% of the acid mixture. After the dilution  the total mass is agitated for about 30 mins. and settled for 8 hrs. The bottom layer comprising 76 77% spent acid is withdrawn. The top layer constitutes sulphonic acid which is also called acid slurry.

Using a mild steel reaction vessel without cooling facilities during sulphonation and a lead lined vessel for the acid separation  the colour of a 10% solution in alcohol of the finished sulphonic acid expressed in terms of Klett units is in the range 110 130. However  using a stainless steel reactor with cooling facilities and chilled water or ice for dilution  a vastly improved colour between 35 and 50 Klett units can be obtained. This improved colour can result in an improved colour of the finished detergent powder or cake.

Sulphonation with 20% Oleum Batch Process

A typical reactor has a capacity of 1 tonne and is made of mild steel. It is fitted with a cooling coil and an anchor type stirrer. The cooling coil keeps the temperature of the reacting mass under control and the stirrer ensures thorough mixing and heat transfer.

The vessel is charged with 500 kg alkylate. The stirrer is turned on and cold water is circulated through the coil. Oleum is metered slowly into the reactor at such a rate that the reaction is completed in two hours. The course of the reaction is followed by the 35% alcohol test.

When the reaction is complete  the mass is dropped into a 1.25 tonne capacity lead lined jacketed MS vessel and allowed to stand for 1½ hours. The material is diluted with 70 kg water over a period of 1 hour using cooling water in the jacket for taking away the heat of dilution and maintaining the temperature at about 65°C. The diluted mixture is further cooled to 40°C and delivered to a 5 tonne vessel for separation of sulphonic acid.

The degree of conversion that can be achieved is 98%.

Sulphonation with 20% Oleum Continuous Process

The continuous process is employed where outputs of the order of 1 tonne of AD per hour and above are desired. There are many variations of which one is called  Cascade process  and will be described briefly (Fig. 1)

Alkyl benzene and oleum are metered into a special pump that mixes and circulates through a heat exchanger. A part is returned to the pump and the remaining portion is passed through what are called Hold Up Coils. The residence time in the coils is approximately 10 minutes and the total reaction time is 15 minutes. The reaction mass then passes to the Dilution Heat Exchanger  the temperature of which is maintained at 68 70°C using a control on the cooling water line. In this heat exchanger  cold water is introduced through a pump that also receives the reaction mass from the Hold Up Coils. The mixture is circulated through the Diluter cum Cooler before it enters the Separator.

The separator is a stainless steel vessel 120 cm diameter with a dished bottom and conical top. The diluted reaction mixture is introduced through horizontal polypropylene pipes with 3 mm holes. The pipes are located in the lower region and cover the entire area of the cross section of the vessel. It is a normal practice to use concentric pipes which help to diffuse the mass gently in order to facilitate separation at a desired rate of 3 ft per hr for a throughput of 1 tonne AD per hr. The separation efficiency depends upon the temperature of the diluted material and the ratio of spent acid to sulphonic acid.

Neutralisation is carried out using pump and heat exchanger as for sulphonation. When caustic soda is used  the flow is controlled on the basis of the pH of the neutralised mass. With soda ash a modified system to facilitate the removal of CO2 gas is used. In this case the sulphonic acid is pre cooled in a stainless steel coil to 30°C and is neutralised in a stainless steel mixer with 16.5 per cent Na2CO3 solution maintained at about 35°C. No cooling is required after neutralisation. The neutralised mass enters a stainless steel vessel fitted with a stirrer and plastic ducting for the removal of carbon dioxide liberated during neutralisation.

Good conversions (98 99%) have been achieved in this continuous process. The AD content of the paste is 42 per cent and sodium sulphate is 6 per cent.

Sulphonation Using SO3 Gas from Oleum

Batch Process

Sulphonation using SO3 gas (gas/liquid reaction) represents an improvement over the use of H2SO4 or oleum (liquid/liquid reaction). The advantages are

The smaller size of equipment for the same throughput

Reduction in spent acid production and

Improved quality and conversion of sulphonic acid.

Sulphur trioxide gas being highly reactive is generally diluted with a dry inert gas such as air  before it is allowed to enter the reactor. It is generated by heating oleum in cast iron stills at a temperature of 250°C. It is a normal practice to use 60% oleum (i.e. 60% SO3 in 40% H2SO4) for generating SO3 since this is more economical compared to 20% oleum.

The reactor is usually a 1 tonne capacity jacketed cylindrical mild steel vessel fitted with a turbo mixer (400/450 rpm) situated near the bottom. The vessel is also provided with cooling coils through which tower cooled water is circulated for taking away the heat of sulphonation.

The flow of oleum into the still is regulated by means of a metering valve. The still may be heated with electricity  gas or fuel oil but the more common heating agent is gas. SO3 gas is fully stripped from oleum at a temperature of 250ºC.

The procedure is to pump 500 kg of the alkylate into the sulphonator. About 5% of concentrated sulphuric acid of the weight of alkylate may be added for controlling the viscosity of the reacting mass and for minimising side reactions  although this is less critical in the case of LAB and more so for DDB alkylate.

Sulphur trioxide gas generated in the oleum still is first diluted with dry air to a concentration of 15% (vol/vol) and introduced at the bottom of the reactor while stirring. The rotor of the turbo mixer creates a suction  which enables the gas to be drawn in. As a further aid  the sulphonator is connected to a vacuum system  which helps to evacuate the spent gases  through a packed tower through which caustic soda solution is circulated for the absorption of the acidic gases.

The reaction is rapid and exothermic. The heat of reaction is dissipated through cooling coils and jacket and the temperature of the mass is maintained at 50 55ºC. The flow of gas is adjusted in such a way that the reaction is completed within 3 hours.

When 96% conversion is achieved  oleum feed to the still is either considerably reduced or discontinued  and the residual gas is bubbled till 98% conversion is achieved. Sulphonation is stopped when the desired conversion is achieved.

It is important to ensure that all the reactants are dry. The presence of moisture leads to the production of sulphuric acid thereby reducing the availability of SO3 for sulphonation. Moisture also contributes to corrosion problems. In actual practice the dry state is rarely achieved and  therefore  corrosion is a common feature of sulphonation plants.

In a batch process  it is fairly easy to control the reaction since for a given quantity of alkylate the quantity of oleum used is fixed.

For drying air there are a number of possibilities. These are

          The use of a sulphuric acid scrubber

          Compression  cooling and silica drying of air and

          Bubbling of air through a pot that receives spent acid from the oleum still. The choice depends upon the initial and maintenance costs. The first two methods can be used efficiently whereas the third one is only partially effective.

A number of safety precautions have to be followed in the handling and storage of oleum. Personnel other than those working in the plant must have no access to the plant. Adequate protective wear such as PVC suits  gloves  goggles  caps and full pants are usually provided to the sulphonation personnel.

A system of planned maintenance of plant and equipment would greatly reduce the time lost due to unforeseen breakdowns. Some of the common problems are corrosion of pipes carrying spent acid from the still  SO3 pipes  still joints  pump glands  metering valves  coil leaks and corrosion of caustic scrubber and vaccum equipments.

The quality of sulphonic acid is routinely checked by the colour reading in a Lovibond tintometer. For a 98% conversion a good colour reading is 7 8 units as Y + 5R when viewed through a 1/4  cell. To achieve a good colour  the design of the turbomixer  feeding rate  dilution of SO3 gas  and temperature of the reaction are important. Sulphonic acid from the batch process is neutralised by dropping the mass into a solution of caustic soda contained in a neutraliser. The mild steel neutraliser is fitted with a paddle type stirrer  and cooling coils. Neutralisation is completed by cooling the mixture to 70°C and stirring at a pH of 8. The resulting paste is bleached with sodium hypochlorite used at a level of 0.5 1% available chlorine on active detergent.

Continuous Process

Earlier  in the continuous process  a number of batch reactors were arranged in a Cascade fashion and the product of the reaction was made to overflow from one reactor to another by gravity. The reaction was thus split between  say  five reactors and the SO3 air mixture was introduced into each reactor in quantities sufficient to achieve the required conversion in that reactor. The finished product with the required degree of conversion flowed out of the last reactor into an ageing vessel and from there to the neutralisers.

The advantage of the continuous process is that once the system is tuned  and with adequate controls of alkylate feed to the first reactor and SO3 flow to individual reactors  very little attention is needed except periodic checking of the degree of conversion of the finished product emerging from the last sulphonator.

Ballestra Process

In this plant  the liquid passes through a number of stirred tanks in series and the SO3/air mixture is fed independently to each reactor (Figure 4). The total number of reactors depends on the capacity required. Cooling is effected by means of external heat exchangers and pumps. The liquid is forced through the heat exchangers at a speed higher than that which is attained in a stirred tank reactor  and this results in a better heat transfer rate  and smaller reactors and residence time.

The gas mixture is introduced into the Ballestra reactor via a number of pipes which are all parallel and connected to a ring main. The number of pipes in a reactor depends on the viscosity of the material in the reactor and the system is designed so that the velocity of the gas leaving the pipes in the first reactor is 40 meters per second and in others  20 meters per second. The source of SO3 gas may be either oleum  or by burning sulphur and oxidising the resultant SO2 gas. Ballestra specialises in the latter process.

Table 2  The Ballestra Process

The principal features of the plant are shown in Table 2. In order to provide a fine control on the degree of conversion  a variable but small proportion of alkylate is reintroduced into the vessel V.

The degree of conversion is measured continuously by following the changes in specific gravity. The signal from the specific gravity measurement controls a motor which adjusts the stroke of a proportioning pump for the last 5% of the alkylate which is fed into reactor V. Actual conversion achieved is in the range of 97 98%.

Neutralization is carried out continuously at 50°C. 90% of NaOH is added at a fixed rate and the pH controller regulates the feed of the remaining 10%.

Film Reactors

The advantages of the film reactor over the stirred tank reactor are short residence time and a more complete reaction. The yields are higher. The side reactions are minimum and hence good colour and odour are obtained. The size of the equipment is also small and consequently the space requirement is less. Some of the common film reactors are manufactured by Chemithon  Allied Chemicals  Mazzoni and Ballestra and these are briefly described below

Chemithon Reactor In the Chemithon process  the reactor is constructed as an annulus with cooled walls. The alkylate is fed to the top of the annulus space  separate feeds being provided for the outside walls (40%) and the inside wall (60%). The feed pipe of the gas mixture (4% SO3) enters the reactor at the base for constructional reasons and meets the liquid by entering the annulus space at the top. Both walls of the annulus are cooled and a stirrer located in the annulus  extends to a height of 37 cm  out of the total length of the reactor of 100 cms.

The material is passed  through a pump/heat exchanger loop for cooling. The heat exchanger has an area of 12 sq.m. for 1 tonne per hr. capacity and cools the sulphonic acid from 100 °C to about 45°C. The residence time is 2 4 minutes.

The foam from recycle tank passes to a cyclone which is flooded continuously with sulphonic acid in order to prevent droplets from drying on the surface of the cyclone and providing discoloured material which will promote the deterioration of the final colour of sulphonic acid.

Allied Chemical Reactor The Allied chemical reactor (Fig. 8) is a film type and consists essentially of a tube 20 mm in diameter and 6 meters long. The flow of liquid through the tube is controlled by gravity and the residence time is very short. The SO3 concentration is 3.5% and the velocity of the gas is 80 m/sec.

The Ballestra Multitube Falling Film Reactor

This unit is based on the multitube film reactor having a number of tubes according to plant production capacity. The sulphonation gas is fed to the top of the reactor and distributed exactly in equal parts into each reaction tube. The raw material is fed in co current with the gas.

An advantage of the Ballestra film sulphonation plant is the special design of the reactor distribution heads which gives the possibility to dose accurately  and to keep the exact mole ratio between the raw material and the sulphonation gas in each single reaction tube and to self equilibrate it  thus eliminating any risk of over sulphonation. This feature is critical when sensitive raw materials such as alcohols and alpha olefins are processed. The exact mole ratio between sulphur trioxide and organic feedstock is essential to obtain the maximum conversion degree with optimum colour.

Mazzoni Multitube Falling Film Reactor

Here  the individual tube reactors are cooled from outside. The organic raw material and the sulphur trioxide air mixture are fed through calibrated nozzles to the individual reactors. Simultaneously  pre dried air is distributed to the individual sectors. This gives uniform pressure in the individual tube reactors and hence the desired ratio of reactants in each tube. The compensating air blends in with the air/sulphur trioxide mixture in the reactors whereby the sulphur trioxide concentration is lowered at the zone of the reaction leading to regulation of temperature.

The reactor consists of a plurality of tubes associated together in a tube bundle arrangement. The reactor head is of three separate chambers for feeding the liquid reactant  the sulphur trioxide gas and the equalising air. Each tube is provided with its own cooling jacket.

Bleaching of Sulphonic Acid The colour of sulphonic acid produced on a commercial scale depends on the technique employed for sulphonation and the quality of the raw materials. A good colour reading of sulphonic acid derived from linear alkyl benzene is 30 35 in Klett units. If such a material is used in the production of a white or blue detergent powder or cake  the colour of the end product would be clean assuming that other ingredients used in the formulation are of normal acceptable grades.

Uncontrolled sulphonation of LAB can often lead to the production of sub standard sulphonic acid in terms of colour which in Klett units can go up to 200 or more. Such a material cannot give a satisfactory end product. For example  the blue colour would appear with a tinge of green and white powder would appear off white.

Sulphonation using sulphuric acid or 20% oleum in a stirred tank reactor can lead to the production of a satisfactory end product  with adequate cooling during sulphonation and separation of excess acid during the subsequent stage. However  if sulphur trioxide gas is used and its dilution with air prior to use in the sulphonator is not ensured  uncontrolled sulphonation leading to the production of dark coloured sulphonic acid can result. When this happens  especially in continuous processes  a large quantity of dark coloured sulphonic acid is obtained. The question that arises then is whether it is possible to bleach them to the required colour standard.

Laboratory scale experiments have shown that it is possible to bleach dark coloured sulphonic acids using a bleaching agent such as hydrogen peroxide. The level of bleaching agent to be used would depend on the initial colour of the acid. However colour reversions have been observed and in most cases the reverted colour far exceeds the original.

It can be reasonably concluded from these experiments that although a colour reduction is observed initially when dark coloured sulphonic acid is bleached with hydrogen peroxide  a colour and possibly odour reversion takes place that exceeds the original. Even after neutralisation of the freshly bleached sulphonic acid results are not entirely satisfactory.

To sum up  laboratory scale experiments suggest that there is no substitute to the production of light coloured sulphonic acid during the production stage itself  rather than an attempt to bleach a dark coloured product for improving the colour.

Neutralisation of Sulphonic Acid

Neutralisation of sulphonic acid can be carried out either separately in a neutraliser or as a part of the slurry making operation prior to spray drying. It is however  more convenient to neutralise the sulphonic acid by dropping it into the neutraliser located beneath the sulphonators  by gravity. This step also enables correction for colour and addition of CMC (Carboxy Methyl Cellulose) and sodium silicate which are normal ingredients in detergent powders. The neutralising agent is caustic soda solution of a suitable strength (approx. 25%) and the common bleaching agent for colour correction is sodium hypochlorite (1% available chlorine on neutralised paste) used at a pH of 8. It is necessary to destroy excess bleaching agent with the help of sodium sulphite or sodium perborate.

Another bleaching agent is hydrogen Peroxide which is milder than sodium hypochlorite.

The neutraliser is a mild steel vessel fitted with cooling coils and a paddle type stirrer with paddles at the top and middle and turbine blades at the bottom. Neutrailisation is carried out by first taking caustic soda solution in the neutraliser and dropping sulphonic acid into it under stirring and cooling. A pH of 8 to 8.5 is maintained and on completion of neutralisation the bleach liquor is added. Bleaching is only carried out if required. With sulphonic acid derived from linear alkylate  bleaching is superfluous since the colour of sulphonic acid is light (45 to 55 in Klett units). After neutralisation  other additives such as CMC and Sodium silicate are mixed and the mass is transferred to storage for use in slurry making prior to spray drying. To minimise the possibilities of separation of silicate water layer from the storage tank  the contents of the tank are stirred continuously.

Sodium hypochlorite can be manufactured at the site by passing chlorine gas at a controlled rate into a solution of caustic soda in a concrete tank under cooling. It is a standard practice to adjust the conditions to produce a bleach liquor with 10% available chlorine. The pH of the bleach liquor is maintained at 8 for stability and excess chlorination should be avoided.

Instead of sodium hydroxide  it is also possible to use sodium carbonate as a neutralising medium. This will however necessitate the use of a large sized vessel for carrying out neutralisation because of the evolution of carbon dioxide and swelling of the mass. The paste also gets aerated in the process and this is not desirable unless a de aeration step is introduced.

 

Chemicals Used in Soaps & Detergents

Alkylolamides

Introduction

Alkylolamides are condensates of alkylolamines and fatty acids and are generally referred to as foam boosters or additives. Their use in detergent formulation goes a long way towards solving the problems of stabilization  improvement and creaming of lather which are so important to the success of compounded detergents. They can be used as detergents in their own right  but probably their main outlet is as ingredients in shampoo and liquid and powder detergent production.

The condensates of commercial interest can be divided into three classes 

          Products from the reaction of one mole of a monoalkylolamine and one mole of fatty acid.

          Products of reaction of one mole of a dialkylolamine with one mole of fatty acid.

          Condensation products of more than one mole of a dialkylol amine with one mole of fatty acid.

The products of the class (1) with free fatty acid contents in the range of 5 10 per cent  are oily light brown liquids which are soluble in water and are quite good detergents particularly for cleaning hard surfaces  walls  tiles  floors etc. These products can be used in the formulation of liquid cleaners  and the following formula has been suggested.

Formula 1

This type of formulation is advocated for packing in mild steel drums for sale to hospitals  institutions  bakeries etc.

The products of the class (2) with low free fatty acid contents are used as foam boosters  particularly in the formulation of liquid cleaners. They also act as solubilizing agents for alkyaryl sulfonates and sodium lauryl sulfates  depressing the cloud points of mixtures and helping to ensure that no separation of active matter occurs at low temperatures. These products are also used to a more limited extent as additives for powder detergents  they are incorporated by spraying in the molten state on to spray dried or physically mixed powders.

The monoalkylolamine derivatives find their major outlet as builders for all purpose spray dried powder detergents  where they are normally used at the level of 1 3 per cent. The range of useful additives is wide  but can be limited to some extent by economic considerations. In the choice of additive for any particular formulation the following points must be considered

          Does the additive have the desired foam boosting properties when added at the desired economic level?

          Are the raw materials available at a reasonable and stable price?

          Can the additive be made consistently or does it suffer batch to batch variation which impairs its properties.

          Is it compatible with other ingredients in formula e.g.  if used with a liquid product  can it be sufficiently solubilized  together with the other solution?

          Can it be easily incorporated at the right concentration in the powder e.g.  can it be sprayed evenly on to the powder  will it be stable at spray drying temperatures  or will it result in a sticky powder and tend to bleed out?

          Is it stable under long term storage conditions or will it turn rancid or affect the perfume in anyway?

          Has it any disadvantages in use  e.g.  does it leave streaks on glasses washed in the detergent solution?

The time taken between laboratory trials and launching a detergent powder on a commercial scale may be anything from six months to three years  depending on time taken for consumer trials  necessary plant alterations  stability testing etc. When asked to recommend an additive for any particular proposed formula  the additive manufacturer must weigh all these points carefully and if necessary  carry out extensive tests. There is no one additive which will perform satisfactorily with all formulae and the additive makers have constantly to be searching for new and improved products  particularly in view of such developments as the increasing use of primary alkyl sulfates in all purpose formulae.

Alkylolamides in Shampoo Formulations

The mono and dialkylolamides are widely used in liquid and liquid cream shampoo formulations. They exhibit additive powers so far as volume of foam goes and also help to ensure the creamy  thick lather desired by the customer. They are of great assistance in thickening liquid shampoos and by their addition to alkylolamine neutralized lauryl sulfate  practically any desired viscosity can be achieved.

An example of a typical formulation for a built medium viscous liquid shampoo using triethanolamine lauryl sulfate is 

Formula 2

In liquid cream shampoos the stearic acid derivatives are commonly used as spacifying agents  although pearliness is generally better achieved by other stearic acid condensation products.

Chemistry of the Alkylolamides

The alkylolamides in common use may be represented by one of the three following structural formulae

They may be looked upon as amides derived by condensing an aliphatic acid of moderate or long chain length with an amino alcohol. However  it does not necessarily follow that amides actually used are produced by direct condensation. The RCO will be derived from buy of the natural fatty acids in the range of capric  caprylic to oleic  and stearic and behenic.

Mono alkylolamides

The substance in class I are waxy materials  and on their own are substantially insoluble in water. The members of this class derived from the fatty acids of moderate chain length such as lauric and myristic can  however  be soluble in water when they form part of a composition with other synthetic detergents which are themselves water soluble. These particular alkylolamides have the power of improving the soil removal efficiency of other detergents  particularly sulfated and sulfonated detergents such as sodium lauryl sulfate and sodium dodecyl benzene sulfonate. They also have the power of enhancing the foaming powers of detergents  particularly those just named  under the appropriate conditions.

Alkylolamide falling in class (1)  but derived from higher fatty acids  are practically insoluble in water and do not improve the lathering power or soil removal efficiency of detergents  but they are valuble emulsifying agents  and in some cases  they serve to render translucent detergent compositions opaque or  pearly  in appearance. It is also stated in the literature that certain alkylolamides derived from higher unsaturated fatty acids are useful as conditioning agents for the hair when incorporated in shampoos. The alkylolamides derived from lauric and myristic acids  which are probably the most used in this class  are generally chosen to enhance the foaming or detergent power of other surface active agents in preparations which are to be marketed as powders. Generally speaking  these alkylol amides  even in the presence of substantial quantities of sulfated anionic detergents  are not sufficiently soluble to enable clear or translucent liquid preparations to be formulated. However  under some conditions in the presence of other materials which act as coupling agents  clear liquid products can be produced. The coupling agents may be aliphatic alcohols or may even be alkylolamides derived from ether fatty acids. As an example of the latter  it may be noted that the mono ethanolamide derived from coconut oil fatty acids which will contain approximately 65 per cent of the lauric and myristic ethanolamides is much more soluble in liquid detergents concentrates than an alkylolamide derived from pure lauric or myristic acid.

Di alkylolamides

The alkylolamides falling in class (2) are more soluble than those in the previous class. Until recently  the alkylolamides in this class were most frequently made not as the pure amides represented by the formula given  but in the form of a complex composed of genuine amide  free amino alcohol and some soap. There is considerable evidence that the complex does not function as simple mixture and in this form many alkylolamides of class (2) are readily soluble in water although they may be salted out by electrolytes under certain conditions.

On account of their solubility in water di alkylolamides derived from lauric or myristic acid and diethanolamine in the form of the complex containing excess diethanolamine have found extensive application in the formulations of liquid detergent preparations. These alkylolamides have the power to augment the foaming power of other surface active agents under certain conditions and at the same time they have a thickening effect upon liquid detergent preparations generally. Unlike the products in class (1)  which are purely effective as improvers for other detergents  the alkylolamides in this class possess  in the form of the complex  very considerable detergent power in their own right and are frequently used without the admixture of other surface active agents in the formulation of the general cleaning and so called  sanitizing  detergent preparations.

The alkylolamides represented by formula (3) are interesting  in that the balance may be altered by varying the number of molecules of ethylene oxide in the two radicals attached to the nitrogen atom. Compounds in this group show reasonable wetting properties and the precise wetting power depends upon the balance of the molecule. Thus if RCO is derived from short chain fatty acids such as lauric or myristic  the wetting power is at its highest when the side chains contain not more than five molecules of ethylene oxide (in other words  when m+n in the formula does not exceed 5)  Whether RCO is derived from a longer fatty acid such as stearic or oleic  it is necessary for the hydrophilic properties of the molecule to be increased to achieve optimum wetting power. In this case  the best results are obtained when the number of molecules of ethylene oxide is about 10 (that is where m+n  10). The alkylolamides  however  in this class have never become as extensive in use as the alkylolamides in the other two groups. They are principally of interest for their value as emulsifiers. The products from coconut oil fatty acids and containing l0/50 molecules of ethylene oxide are good oil in water emulsifiers for carnauba wax.

Pure Di alkylolamides

Until recently  the alkylolamides in class (2)  have generally been available and used in the form of a complex. This was in many ways convenient  as the complexes were more soluble and possessed better wetting and detergent power  than the pure amides  and also because it is simpler  and therefore cheaper to manufacture this type of product free from undesirable by products if an excess of alkylolamine is present. Where  however  these products are used in conjunction with sulfated detergents to enhance the foam of the latter  the effective material is the true amide  while excess diethanolamine contained in the complex does not contribute towards the effect. In cases such as these  the di alkylolamides can normally be adequately solubilized by the sulfated detergent and therefore the excess diethanolamine serves no useful purpose.

For the majority of applications  however  the whole issue would seem to hinge on the price one is paying for 100 per cent active amide when one buys it in the nearly pure state  as compared with the conventional complex. It cannot  of course  be overemphasized that where di alkylolamide is being used as a detergent in its own right  alone or with only minor amounts of other detergents  the  complex  will of course be preferred on account of its all round greater solubility and wetting and detergent power.

Phosphoxylated Alkylolamides

Recently  interest has been taken in the production of phosphoric acid esters of the alkylolamides. These have been claimed to have an anti static effect when used in the washing of synthetic fibres such as nylon. Other phosphoric acid esters of alkylolamides have found application to produce a  pearly  effect in some types of cream shampoos.

Sulphated Alkylolamides

The product so far described  where they have been soluble in water and possessed surface active properties  have been essentially non ionic in their behaviour. It is possible by preparing the acid esters of sulfuric acid or phosphoric acid of these alkylolamides to produce detergents which are anionic in their behaviour. In general the mono alkylolamides falling in class (I) are preferred for sulfation of phosphorylation. The sulfated mono alkylolamides of coconut oil fatty acids have excellent lathering power comparable with that possessed by sodium or triethanolamine lauryl sulfate. They show a superior detergency to the latter materials  and also greater ability when in dilute solution to retain dirt particles in suspension.

The sulfated alkylolamides  however  are not one of the big volume detergents and they have never equalled the alkyl sulfates in popularity. Probably one of the reasons for this is that it is extremely difficult to control the sulfation procedure to ensure that the finished product is free from undesirable by products  which impair efficiency. The fact that on paper the preparation of sulfated alkylolamide detergents appeared relatively easy  at one time tempted some firms to try and produce these materials without adequate research. The earlier products  however  were very variable and frequently contained substantial amounts of undesirable side products. Properly prepared  however  the sulfated alkylolamides are excellent products. Probably the best known of this type of detergent is the sulfated monoethanolamide or isopropanolamide derived from coconut oil fatty acids. Detergents have been prepared  however  from higher unsaturated fatty acids  and though under some conditions they lack the lathering power of the products from coconut oil  they do possess exceptionally good detergency and also  incidentally  exceptional power to disperse lime soaps.

Whereas the sulfated fatty alcohols are generally processed so as to ensure the maximum degree of sulfation and the minimum residual amount of unsulfated fatty alcohols  it is not usual  in the case of such materials as coconut oil fatty acids monoethanolamide to secure such a high degree of sulfation. Frequently 75 per cent to 85 per cent sulfation is the maximum desired. The reason for this is that unsulfated alkylolamide acts as a builder for the sulfated product and such a mixture of sulfated and unsulfated material is very effective in use. Products containing as much as 50 per cent unsulfated material (provided always that they are free from undesirable side reaction products) have excellent lathering and cleaning power.

Foam Stabilization

The original patents which referred to the use of alkylolamides in detergent compositions were mainly concerned with the improving effect that the alkylolamides exerted upon the soil removal efficiency of other detergents. However  alkylolamides today are most frequently added to detergent compositions in order to improve the lathering power under the conditions of use. When we come to consider how to estimate quantitatively the effect of the alkylolamides  the position is by no means simple. Many compositions in practical use are improved by the presence of an alkylolamide. However  it is not always easy to measure this improvement quantitatively under laboratory conditions. For example  it is often quite useless attempting to infer how a shampoo composition will behave in use of the hair by measuring the foam obtained by shaking solutions of the detergent preparation in measuring cylinders in the laboratory.

One satisfactory way consists in devising a laboratory test  which simulates the actual conditions under which a detergent product is to be used. The effect that an alkylolamide exerts upon the foam of a preparation when the foam is created in narrow capillary in a relatively narrow foam cylinder is quite different from that exerted when the foam is produced on a wide surface area such as one has in a sink during dishwashing operation. The conditions which apply during a shampooing operation on the hair are different again. It is further most important that  in tests designed to evaluate detergent preparations in the laboratory  soil such as would be expected in actual practice should be present. It is also important that the tests should be carried out at the same active detergent concentration as would apply in practice.

The effect of concentrations on lathering power is readily illustrated by an example concerning the sulfated alkylolamides. Salts of sulfated lauric acid mono ethanolamide possess excellent lathering power at high concentrations such as might be employed in shampooing or for the washing of clothes under domestic conditions  but if a solution of the detergent is excessively diluted  once the detergent concentration falls below a certain critical level the foaming power disappears. Sulfated alkylolamides derived from C19 unsaturated acids  however  behave quite differently. These give very little lathering at high concentrations. At high dilution  however  at a similar concentration level to that at which the sulfated lauric mono ethanolamide would have ceased to lather  these produce an extremely stable foam. The detergent concentration in a washing machine in a commercial laundry would be at a low level.

Another interesting method for testing a shampoo product under pratical conditions has recently been described in the literature. The effect of alkylolamides on sulfated and sulfonated anionic detergents is not normally to improve the lathering power of the detergent in plain water. Alkylolamides offset the deleterious action of oily or fatty soiling matter on the foam of these detergents. Many anionic detergents  though they lather well in plain water tend to lose their lather to an astonishing extent in the presence of oil and fatty soiling matter and this effect is prevented by the use of suitable alkylolamides. The effect  however  is not quite true at all concentrations and the effectiveness of the alkylolamide only takes place above a certain threshold concentration of active detergent in solution. Fortunately his threshold concentration where lauric or myristic monoalkylolamides or dialkylolamides used in conjunction with such detergents as the alkylaryl sulfonates or alkyl sulfates is below the concentration at which most domestic washing operations are carried out.

An alkylolamide of much higher threshold concentration is capable of improving the lather of anionic detergents at high concentrations (e.g.  3 per cent and over) such as would be used when shampooing the hair. Where  however  the dilution becomes much greater  the lathering power rapidly diminishes. Thus  using this particular alkylalimide  it is possible to prepare a composition  which yields a rich stable foam on the hair  but immediately the rising operation commences  the foam disappears. This effect would not appeal to consumers who like to judge the lathering power of a shampoo by the amount of lather to be seen in the wash bowl after rinsing. However  it would appeal to those who find stable detergent foams difficult to rinse away  down the sink and to the sewage authorities who find stable detergent foams so difficult to handle.

The most commonly used alkylolamides for the purpose of stabilizing foam are the monoalkylolamides  which fall in class (1)  and the alkylolamides  which fall in class (2)  derived from either lauric or myristic acids. Products derived from mixed fatty acids containing substantial proportions of lauric or myristic acid such as coconut oil or palm kernal fatty acids are also used. In general  however  when one comes to measure effective foam stabilization as such  it is generally found that the products derived from mixed fatty acids associated with them behave virtually as no more than inert diluents  although in the case of the monoalkylolamides  products from mixed fatty acids sometimes have the advantage of greater solubility in liquid detergent preparations. Therefore  it is frequently a better economic proposition to buy what is initially a more expensive product devised from a fractionated lauric acid than to use a mixed product which has a lower market price.

These observations apply to the stabilization of foam and there are  of course  other aspects of the use of alkylolamides where the mixed products may be more worthwhile. Generally the lauric monoalkylolamides are preferred for use in powder compositions. Frequently  they are here associated with polyphosphates  and in the case of some alkylolamides  particularly isopropanolamides  the presence of polyphosphates seems to be necessary for the maximum stabilising effect to be produced. The monoalkylolamides are generally dispersed in detergent slurry at an elevated temperature before it is mixed with the phosphates or other builders and fed to the spray drier. Mono alkylolamides are now available in powder form  which greatly facilitates the operation of dispersing them in a detergent slurry. Lauric diethanolamides either in the form of complex previously referred to  or in the pure state  are used in the formulation of liquid detergents since they do not impair the cloud point of these products in actual fact  diethanolamides in the form of the complex frequently effectively lower the point at which alkylaryl sulfonate and other compositions cloud. However  there is no hard and fast rule concerning the use of the different types of alkylolamides. Dialkylolamides may be incorporated into powders in quite significant amounts and  on the other hand mono alkylolamides may be included in liquid composition either in restricted amounts alone or solubilized by the addition of alcohol.

Manufacture of Alkylolamides

Most of the alkylolamides manufactured in India are derived from ethanolamines and fatty acids like stearic  lauric  coconut  myristic and oleic. The general method of preparation of these compounds involves the use of low molecular weight aminohydroxy compounds and acylation of amino ( NH2) group with higher fatty acid.

Amino group may be primary or secondary. Also hydroxyl group may be more than one.

Sulfated product of monoethanolamine of coconut fatty acids is an important compound. It may be prepared by heating equimolar quantities of fatty acids and monoethanolamine at 170°C. The intermediate amide so produced is sulfated with sulfuric acid at 300ºC. Otherwise the sulfuric acid ester of ethanolamine in alkaline solution may be condensed with fatty acid chloride.

COCI + NH2.C2H4.CSO3Na  RCONH C2H4.CSO3Na

In this process however  small amount of the ester RCOOC2H4N5 is also formed which detracts activity. Other acids like palmitic solids  oleic and palm oil may also be used.

The manufacture of alkylolamides is carried out in a stainless steel factor fitted with an agitator and a thermocouple. The reactor is jacketted for steam  electric or oil heating. The process of manufacture is briefly outlined below.

Coconut Fatty Acid Diethanolamide

It is a yellow viscous liquid  which finds application as a foam booster in the manufacture of detergents and shampoos and also as an emulsifier and a solubilizing agent. Its composition is usually  60 70 per cent amide  1 percent water  and 7 percent ester. pH of 1 percent solution of this compound is 8 to 9. Its manufacturing process is as follows

Charge the reactor with 60 kgs. coconut fatty acid and 63 kgs. diethanolamine. Switch on the heaters and regulate the speed of stirrer to maximum so as to mix the reactants properly. When the temperature reaches 130°C  pass nitrogen gas in the reaction mixture. See that the reaction mixture is thermostatically adjusted to 165ºC. As the reaction progresses  the acid value of the product falls down which is to be determined every half an hour interval. The reaction is stopped when acid value falls to 5.

Lauric Acid Diethanolamide

Lauric acid diethanolamide is a white waxy material having the composition amide  90 per cent  water 0.5 per cent  ester 5 6 per cent  and free amine 1.2 to 3.0 per cent. It is used as a foam stabilizer  as a superlatting and thickening agent in the manufacture of shampoos and detergents  and as a perfume fortifier in soaps. It is prepared as follows

Charge reactor with 60 kgs. lauric acid and 63 kgs. diethanolamide. Switch on the heaters. When temperature reaches 50°C  allow nitrogen gas to flow in reactor. Carry out the reaction at 170°C till the acid value drops to 5.

Oleic Acid Monoethanolamide

It is in amber coloured viscous liquid soluble in naphtha and kerosene. Its composition in 85 per cent amide  1 per cent water and 7 8 per cent ester. It is used as a foam stabilizer and as a superfatting and thickening agent for shampoos and detergents. It is prepared as follows

Charge reactor with 84 kgs. double distilled oleic acid and 18 kgs. of monoethanolamine. Switch on the heater and stirrer. When the temperature reaches 120°C  allow nitrogen gas to bubble in reaction mixture. Adjust temperature to 170°C. Check acid value of the product every half an hour till it drops to 5.

Stearic Acid Monoethanolamide

It is a cream coloured waxy product having the composition amide 90 per cent  ester 5 per cent  water 10 per cent and amine 2 3 per cent. It is incorporated in toilet soaps and detergent cakes for foam stability and viscosity. It is prepared as follow

Charge the reactor with 85 kgs. stearic acid and 18 kgs. monoethanolamine. Raise the temperature to 100°C and bubble nitrogen gas in the reaction mixture. Adjust temperature to l70ºC and check acid value of the product every half an hour till it falls to 5.

In addition to the methods described above there are several other processes available for the manufacture of these and other alkylolamides. The first alkylolamides were prepared about forty years ago. The first patents for preparing alkylolamides were granted to W. Kritchevsky (See U.S. Patents  2 089  212  and 2 096  749) in 1937. They covered the condensation of fatty acids  their triglycerides  esters  amides  anhydrides and halides with not substantially less than two moles of an alkylolamine. The reaction was carried out at 100 to 300ºC  below the decomposition of the resulting product and at atmospheric pressure.

An improved process for making alkylolamides was revealed in a 1949 patent (U.S. Patent 2 464 094) to Edwin M. Meade. This process comprised mixing an ester of an aromatic or aliphatic carboxylic acid with an alkylolamine  adding an alkali metal alkoxide catalyst and heating the mixture to 100ºC at atmospheric or above atmospheric pressures.

In 1958  Giuliana C. Tesoro patented a refinement of the Meade process (see U.S. Patent  2 844 609). It consisted of reacting a fatty acid ester or glyceride with a primary or a secondary alkylolamine in the presence of a sodium methoxide catalyst at a temperature between 55 and 75°C and under a reduced pressure of 40 to 60 mm of mercury.

A continuous process for making fatty alkylolamides in a thin film reactor is covered in a 1958 patent (U.S. Patent 2.863 888) issued to Jack W. Schurman. The reaction involved condensation of a methyl ester of a fatty acid with a mono or dialkanolamine  in the presence of an alkali metal  alkali metal alkoxide  or alkali metal amide catalyst. A short contact time in the reactor produces a high purity alkylolamide.

More recently (1962) Robert Ernest has patented (U.S. Patent 3 024 260) another process for making high purity alkanolamides. A fatty acid is first reacted with an excess of alkylolamine  forming amine and amide esters in addition to the intended unsubstituted alkylolamide. In a second step involving an alkali metal catalyst  the amine and amide esters are converted to the unsubstituted alkylolamide.

John W. Lohr was also granted a patent (U.S. Patent 3 040  075) in 1962 for a process of making high purity alkylolamide by condensing a dialklyolamine with a fatty triglyceride  then adding phosphoric acid to remove the excess a mine and most of the glycerine byproduct.

There are two types of alkanolamide products Kritchevsky types liquid product and the super  amide  product. The first is made by reacting an alkylolamine with a fatty acid or fatty acid derivatives at elevated temperatures in a 2 1 ratio. Such a product contains 60 70 per cent alkylolamide  plus some amine esters and diesters  and piperazine derivatives that are formed by side reactions. In addition  there is significant unreacted alkylolamine. This excess alkylolamine renders the Kritchevsky type alkylolamines water soluble.

The second type of alkylolamide is prepared by reacting an alkylolamine and a fatty acid ester in a 1 1 ratio. These are generally solid products which have an alkylolamide content above 90 per cent. Some of the same by products formed in preparing 2 1 alkylolamides are likewise formed in preparing super amides  but in much smaller quantities. For this reason and because they contain only relatively small amounts of free alkylolamine  super amides have poor water solubility. They are therefore always used in conjunction with a small amount of anionic or non ionic surfactant  which act as a solubilizer  converting an aqueous alkylolamide despersion into a viscous  clear solution.

The starting materials for the super amides are the methyl esters of fatty acids prepared by the displacement of the glycerol in a fat by a methyl alchohol. The process described by Bradshaw in Soap  18  5 23 24  69 70  is remarkable not only for producing methyl or ethyl esters directly from the fat without intervening hydrolysis  but also for taking place at low temperatures  and requiring no alloy steel or other special corrosion resistant equipment.

The reaction is carried out in any convenient open tank  which may be constructed from ordinary carbon steel. The fat must be clean  dry and substantially neutral. It is heated to about 80°C and to it is added commercial anhydrous methyl alcohol (99.7%) containing 0.1 0.5% sbdium or potassium hydroxide. The quantity of alcohol recommended is about 1.6 times the theoretical requirements of the reaction  although amounts as low as 1.2 times theoretical may also be used. Alcohol amounting to more than 1.75 time the theoretical quantity does not materially accelerate the reaction  and interferes with subsequent gravity separation of the glycerol.

After addition of the alcohol  the mixture is stirred for a few minutes and is then allowed to stand. Increased percentages of NaOH or KOH speed up the reaction and increase the conversion. The glycerol begins to separate almost immediately  since it is virtually anhydrous and much heavier than the other liquids  it readily settles to form a layer at the bottom of the tank. Conversion of the oil to methyl esters is usually 98 per cent complete at the end of an hour.

The lower layer of glycerol contains not less than 90 per cent of glycerol originally present in the fat  the upper layer consists of the methyl esters  most of the unreacted alcohol and alkali  the remainder of the glycerol  and a small amount of soap. The impurities are removed from the esters by successive washes with small amount of warm water.

The methyl esters may be fractionated to give rather pure methyl esters of specific fatty acids. To produce the super amides  with 1 mol of methylesters l.l mole of diethanolamine is used along with 0.25 per cent be weight of the total charge sodium methylate as the catalyst. The reaction is best carried out at 105ºC for 3 3½ hrs. Methyl alcohol is liberated during the reaction  and may be reused for ester interchange. The progress of the reaction may best be controlled by collecting and measuring the liberated methyl alcohol.

The monoethanolamides and monoisopropanolamides are wax like substances  practically insoluble in water  but solubilized by another hydrophilic anionic or non ionic detergent and are very easy to manufacture. The production process consists in simply heating stoichiometric amounts of fatty acids with monoalkylolamine at about 160°C for 2 3 hrs. A very slight surplus of monoethanol amine increases the speed of reaction  and can be distilled all at the end of the reaction either under atmospheric pressure or under reduced pressure.

Table 1  gives the settling point and man uses of various monoethanolamides and monoisopropanolamides. The isopropanolamides show a lower setting point than the ethanolamides of the same fatty acids. These products are usually marketed in the form of flakes produced by running the molten products over drilling rolls fitted with doctor blades for scraping off the flakes.

Table 1  Setting Points and Applications and Uses of Alkylolamides

N Acyl N Alkyltaurates

Introduction

N acyl N alkyltaurates have a general formula  RR NCH2 CH2SO3Na  where R may be oleoyl  cocoacyl  tall oil or tallow group and R  may be a methyl or cyclohexyl group. However  the most commonly used and produced product in this group of compounds is sodium N Oleoyl N methyltaurate. It is sold throughout the world under various trade names  most common among them being IGEPON T.

Igepon T was first introduced in 1931  by I.G. Farben industries in Germany and is still in the market in its original form. It is sufficiently stable for most textile processing work except the carbonizing of wool where a strong sulfuric acid bath is encountered. Igepon T has enjoyed a steady expansion of market upto the present time in U.S.A. and Germany and most other developed countries inspite of the advent of alkylbenzene sulfonates. In India  however  most of its requirements are met through imports.

R1 represents hydrocarbon radicals of the fatty acid series which for economic reasons may contain twelve to eighteen carbon atoms. R2 represents an alkyl or cycloaliphatic group which should range from one to eight carbon atoms. Total carbons in Rl and R2 preferably should not be less than twelve nor more than twenty one. Beyond these limits the quality of the product falls off sharply in one of several properties. R3 may be a metal or an organic base or hydrogen. A computation of the number of possible products under the above stated limits might reach 1000.

The effect of changes in structure are fairly well defined. Little detergency is obtained unless R1 and R2 combined contain at least twelve carbon atoms. Detergency is increased by increasing the length of either R1 or R2 or both. The limit is reached at approximately sixteen carbon atoms for R1 if the chain is straight and saturated. If unsaturated  then maximum detergency occurs at approximately eighteen carbons and it is believed that with more unsaturation the maximum length of carbons is further increased. Departures from straight chain in R1 by branching or by introduction of a solubilizing group  will decrease detergency but increase the wetting power. A decrease in the length of R1 increases both solubility and wetting power. If R1 is kept within twelve to sixteen carbon atoms and if the size of the R2 group is increased from a methyl to a higher homolog such as the butyl or amyl group  the resulting Igepon becomes more soluble inspite of the molecular weight increase. If R1 is twelve carbons  the solubility of the Igepon passes through a maximum when R2 is a four carbon straight chain. Wetting increases with increase in the lengths of R2 until R1 and R2 combined contain approximately eighteen carbons. Further increase in R2 brings on a decrease in wetting. R2 may be hydrogen  but when a taurine is used a substitution of at least one carbon group enhances the properties of the resulting product tremendously. The choice of a metal for R3 may affect foaming and the power to emulsify and disperse other substances. There is little difference in solubility between the sodium and potassium salts in the Igepon compounds investigated. The calcium salts are much less soluble. The representative types of Igepon T  currently manufactured in developed countries such as U.S.A. and Germany are given in Table 2.

Although one primary factor in determining which Igepon type compounds will be commercially important is the cost of raw materials  the economic limitations still permit a relatively wide area of investigation. The product derived from oleic acid and N methyl taurine provides the optimum combination of desirable properties. This compound is further recommended by the relatively low price of its raw materials.

Applications of Igepon T Products

Igepon T finds its greatest use today in the textile field where it was first introduced. It finds its way into almost every phase of textile wet processing. The list of uses include scouring  wetting out  degumming kier boiling  dye leveling  dye pasting  chlorine and peroxide bleaching  fulling  lime soap dispersing and finishing. It also finds application in agriculture  paper  leather and metal cleaning  and also to a small extent in household products  including dentrifices  shampoos  cosmetics  and pharmaceutical preparations. It is also used in the scouring of feathers  in electrolytic plating baths  in the washing of automobiles  airplanes  railroad coaches and locomotives  rugs  floors  buildings and for cleaning streets and roads  and in the dairy  food and for industries.

Table 2  Representative Igepon T s Manufactured in U.S.A. and Germany

Igepon T can be prepared in a variety of forms. One is a clear liquid suitable for incorporation into consumer products. It looks much like a conventional liquid soap and is available with 15 and 25 per cent active ingredients. Another form  is a  slurry  or an opaque heavy liquid. This material contains 28 per cent active ingredients and is essentially the product as it comes from the condensation kettles  it contains no added chemicals. It may be used by formulators who will process it further by adding it to other ingredients or drying it to a powder. It can be shipped in tank cars and is the least expensive of the various Igepons.

Future of Igepons

The future of Igepon T  its analogs and homologs  is bright. The economic existence of this type of product is assured by the fact that the biggest weight in its molecule is a fatty acid. The principal fatty acid used is oleic acid  which is found abundantly in vegetable and animal oils. As synthetic detergents derived from non fatty soures encroach on the soap market  the fats and particularly tallow from which oleic acid is largely derived will tend to become more a surplus product.

Another advantage enjoyed by the taurine type Igepon (N acyl N alkyltaurates) is the fact that the Igepon T gel  largest seller in the group today  is not the best wetter in the series  nor is it the best emulsifier or dispersant. It is not the best foamer  the best textile softening agent  or lime soap dispersant  nor is it the most soluble member of the group. It has a good high average on all counts  which led its developers to call it the  universal soap . The taurine type Igepon can be modified to well over 100 varieties. Anyone of the various surfactant properties may be obtained to a high degree by making changes in the structure of the Igepon molecule. Consequently  it is predicted that the Igepon type surfactants will have an important future in the development of special purpose products where price is not the primary consideration.

Manufacture of Igepon T

Raw Materials

The major materials required for the production of sodium Noleoyl N methyltaurine are oleic acid  phosphorous trichloride  N methyltaurine and caustic soda. It is extremely important that a high quality of oleic acid be used in the process. If an excessive amount of esters or unsaponifiable material is present  the resultant Igepon will have an excess of free fat which tends to make the gels cloudy.

The N methyltaurine may be used as a 25 to 30 per cent filtered aqueous solution. The 30 and 50 per cent caustic soda solutions and the hydrochloric acid used to control the pH of the batch at various points in the processes can be the standard commercial products.

Oleic Acid Chloride

The first step in manufacturing Igepon T gel or Igepon T powder is the production of oleic acid chloride (oleoylchloride) from oleic acid and phosphorous trichloride. Acid chlorides other than oleic may be used to make special Igepon compounds.

The reaction takes place in a jacketted lead lined kettle equipped with both cooling water and low pressure steam connections. A horse shoe type agitator stirrs the charge. A 1.5  lead vent to the roof of the building removes volatile acid fumes and decomposition products of phosphorous trichloride from the kettle. It is essential that the kettle be dry before charging is begun to prevent hydrolysis of the phosphorous trichloride. If any condensation accumulates on the kettle due to extended inactivity  it is driven off by introducing steam into the jacket while the kettle is empty.

To begin the operation  oleic acid is blown by air from a feed tank to a steel weigh tank  phosphorous trichloride is similarly blown into a lead lined weigh tank. A 400 kg. charge of acid is drawn from the weigh tank and dropped by gravity into the kettle. Phosphorous trichloride (103 kg.) at room temperature is introduced from the weigh tank over a period of one hour while cooling water is circulated through the jacket of the kettle. A sight glass in the lead line through which the phosphorous trichloride is charged permits the operator to judge the flow rate of this stream. After the kettle has been completely charged the temperature is raised to 50°C to 52°C and is held there for 6 hours by introducing 15 kg. steam into the jacket. At the end of this period the temperature is raised to 60°C for an additional 15 minutes to ensure completion of reaction.

The finished product is blown by air pressure into two lead lined cone shaped tanks and allowed to stand overnight to settle out the by product phosphorous acid. The bases of the cones are heated with extended 1.5  lead steam coils to thin down the heavy acid sludge and aid in the separation. After drawing off the first waste acid the contents of the cone tanks are agitated and then a second separation of acid is drawn off. The point of separation is determined by observation through sight classes in the draw off lines. The spent acid is piped direct to the sewer through lead pipes traced with 1.5  outside diameter pipes carrying low pressure steam.

Oleic acid achloride will descompose on standing if exposed to atmospheric moisture consequently it is made up only as needed and is piped through steam traced lead lines direct from the cone tanks to the weigh tanks of the Igepon unit.

This product is made in a brick lined kettle equipped with a four fingered stainless steel agitator. A stainless steel submerged coil provides temperature control. The kettle has stainless steel feed lines for oleic acid chloride and hydrochloric acid and caustic solution. a stainless steel thermometer well  and a lead vent pipe. Air for forcing the charge out of the kettle is introduced into the vent pipe.

A stainless steel kettle  equipped with an anchor type agitator is also available. Process temperatures in this kettle are controlled by a steel jacket connected to both steam and cooling water lines. Inlets and vents are arranged similarly to those in the larger kettle.

To begin the batch 25 to 30 per cent aqueous solution of N methyl taurine is blown over from the storage tanks until an amount of solution equal to 89.25 kg. of N methyltaurine has entered the weigh tank. The correct gross weight of this charge  based on the N methyltaurine analysis of the storage tank  is supplied to the operator by the analytical laboratory. This charge is then dropped by gravity into the reaction kettle and the flow of cooling water is started in the jacket to bring the temperature of the charge down to 22° to 25°C. Water weighed in the same weigh tank is then added to bring the total weight of the charge at that point to 1296 kg. Addition of 30 per cent aqueous caustic solution is begun and when the equivalent of 14.25 kg. of sodium hydroxide has been weighed in  oleic acid chloride is introduced from a lead lined weigh tank.

The caustic and acid chloride enter the kettle through separate perforated stainless steel pipes below the level of the initial taurine charge. This practice minimizes the liberation of noxious fumes  reduces the corrosive effect of the acid chloride above the liquid level  and safeguards against side reaction between sodium hydroxide and oleic acid chloride.

Simultaneous addition of the two reactants is continued for 4 to 6 hours until a total of 43.5 kg. of sodium hydroxide and 214.2 kg. of about 92 per cent oleic acid and chloride have been charged. The rate of addition of these two solutions is adjusted to maintain a slight stoichiometeric excess of sodium hydroxide in the kettle at all time as determined by spot tests on triazine paper 2 (4 nitro O tolyldiazoamino 4 sulfobenzoic acid).

After all the reagents have been added  the charge is agitated for an additional hour to ensure completion of reaction. Cooling water is circulated through the coils at maximum flow rate during the entire reaction period. During the winter months the temperature of the charge is about 22°C at the beginning of the reaction and rises to 27°C. However  in the summer time the final temperature may go as high as 40°C.

After the reaction has been completed a sample is taken and the percentage of excess N methyltaurine is determined by coupling with diazotized m nitraniline. It is desirable to have a slight excess of N methyltaurine in the product to ensure that the reaction has gone to completion. After completion of the reaction hydrochloric acid is added to the kettle through a glass and rubber siphon from a carbon mounted on a platform scale. Acid is added until the charge gives a slightly red spot test with brilliant yellow paper (pH 6 to 8). This neutralization usually requires about 15.3 kg. of acid. In making some of the special Igepon products additional hydrochloric acid may be needed at this point.

In making the standard T gel the neutralized batch is diluted to 1734 kg. with water and 0.725 kg. of a light floral  liquid perfume. The charge is then heated to 55°C and held there for 1.5  hours. The charge is blown into white oak  gum or ash wood barrels. Air used to blowout the batch passes through a trap to remove rust particles which would tend to darken the finished product. As a further precaution against contamination  a 0.007  opening stainless steel filter on the product discharge line removes all solid particles from the liquid product before it enters the shipping containers. The barrels are allowed to cool on the shipping platform  and when the Igepon reaches a temperature of about 40ºC it sets up as a firm  opalescent gel.

Igepon T gel may be shipped in polyethylene lined  fibre board drums or wooden barrels. The batch yields about 1090 kgs. gel. having a composition of 15.3 to 16.3 per cent Sodium N oleoyl N methyltaurine  0.8 to 1.0 per cent sodium oleate  0.14 per cent N methyltaurine  4.0 per cent sodium chloride and 78 per cent water. This represents approximately the theoretical yield.

Igepon T Powder

In manfacturing this product the initial charge of 30 per cent N methyltaurine solution contains 95 kg. of 100 per cent N methyltaurine  and when diluted with water to 1224 kg it gives a slightly more concentrated solution than that used in the gel process. As a 30 per cent solution 17.6 kg. of sodium hydroxide are added to this intial charge to keep the reaction mixture on the alkaline side. Then 226.5 kg. of technical oleic acid chloride are added simultaneously with 30 kgs. of sodium hydroxide as a 30 per cent solution over a period of 4 to 6 hours  as in gel production.

The batch is stirred for 1 hour after charging is completed and any excess of N methyltaurine is reacted with additional acid chloride and caustic soda as in the production of gel. The completely reacted charge is then heated to 50°C by the steam coils and neutralized to the brilliant yellow and point with hydrochloride acid. Immediately after neutralization 530 kgs. of common salt are dumped into the batch from bags  and water is added to bring the total weight of the batch to about 2652 kgs. At this concentration  about 36 percent solids  the salt is completely dissolved. It is important that no suspended solid material remains in the charge because it would plug up the nozzles of the spray drier. If the pH of the batch after the addition of the salt does not fall between 7.1 and 7.3  sodium hydroxide or hydrochloric acid is added to adjust the pH within these limits.

The salt loaded mixture is blown from the reaction kettles into a 3/8  lead lined sted feed tank. The charge is heated to 50°C by lead steam coils in the feed tank  and then is pumped to the three 10 gallon feed pots of the spray dryer. The dryer atomizers use air at 80 Ibs/in2  pressure heated to maintain 50 Ibs. pressure at the injection nozzles to ensure adequate atomization in the tower. Air supplied to top of the dryer is preheated to about 225°C  by an oilfired furnace and forced into the dryer by a centrifugal fan at a rate of about 250 cubic feet per minute. The major part of the dried powder is discharged from the bottom of the dryer tower and carried along by the added cold air into the primary cyclone separator from which it drops directly into a transfer drum. About 10 per cent of the product  however  is carried through the cyclone and is re introduced into the dryer chamber. A second take off from the dryer chamber is located just above the bottom taper. This duct carries a more dilute stream of air borne powder into a larger  secondary cyclone separator. The solids  which fall out in this separator  are refluidized by more cold air and returned to the top of the primary cyclone. The overhead from the secondary cyclone  containing 7 to 10 percent of the product is introduced into a water scrubber. One water spray above the inlet and three below remove all but about 2 per cent of the product from the dryer exhaust. The scrubbed air is vented to the atmosphere. The liquor is drawn from the bottom of the tower into a storage tank. Make up water is added to this tank by an automatic level control. A high silicon iron pump  drawing from the tank  recycles water to the spray nozzles and supplies process water to the condensation kettle.

If a kettle batch is made each day the dryer feed pots can be kept full and provide an uninterrupted feed to the dryer. Under these circumstances the dryer can handle as much as 180 to 200 kg. Igepon per hour  as it has a rated capacity of 335 kg. water per hour. The product comes from the dryer as low density granules which are lightly milled in a paddle mixer to break up the larger lumps and to mix in 500 grams of a light floral perfume per ton of Igepon. From  the mill the powder is dropped directly into the open top steel drums in which it will be shipped. Yields of powdered product run about 836.4 kg. per batch and analyze about 30.5 to 32.5 per cent oleoyl methyltaurine  1.5 to 3.0 per cent sodium oleate  and 0.14 to 0.8 per cent N methyltaurine  the remainder of the powder comprises inorganic salts. Chief among these is sodium chloride and a trace of sodium sulfate. However  phosphite salts (about 3 per cent) are also present  these are formed from the excess phosphorous trichloride dissolved in the oleic acid chloride. The yield is about 91 per cent of theory.

Chemical Control

Chemical control on the Igepon T operation is relatively simple. By experience  rule of thumb knowledge can be accumulated  which tells the operators whether the reaction is going properly. At some points analytical samples are taken merely as a precaution and only analyzed if trouble develops later in the operation.

The phosphorous trichloride  oleic acid and N methyltaurine are checked for rigid spacifications each time a shipment of materials arrive at the factory. The acid chloride charged to the reaction kettle is analyzed the oleic acid chloride  phosphorous trichloride  and free fatty acid. After the condensation is complete the batch is checked for pH and residual N methyltaurine. The pH is checked by a standard calomel cell pH meter and is then adjusted as explained in the operation procedure.

After the pH has been adjusted it is checked again  and the final shipping sample is sent to the laboratory. This final sample is examined for clarity  viscosity  and alkalinity. A 10 per cent water solution of this sample must be perfectly clean and must have a pH between 7.2 and 7.5 at this point.

The Igepon T powder undergoes an almost identical analysis routine. If the content of oleoylmethyltaurine falls outside of the permissible limits  it is blended into the subsequent batches at the ribbon blender.

Utilities

In the Igepon process steam is used only for process heating. Since the temperatures required are all reasonably low  steam at 100 psi is adequate for this operation. Compressed air is used in the plant for forcing liquids from one vessel to another  the 45 psi air is sufficient. The air used for transfering phosphorous tricoloride is passed through a dryer and filter to present hydrolysis and contamination. The purifying unit consists of a liquid trap  a steel chamber 12  in diameter and 6  long filled with quick lime to dry the steam  and a similar tank 4  long containing a cloth bag filler to remove any particles of lime or other solids that might be carried over into the phosphorous trichloride tanks.

The spray drier may have a separate compressor which provides 90 lb/in2 air for atomization.

Materials of Construction

The corrosion problem is not critical in the operations as described  but some special materials must be used. Carbon steel is suitable for most vessels. However  those which must contain phosphorous trichloride or oleic acid chloride are homogeneously lead bonded. This type of lining is applied by tinning the entire inner surface of the steel vessel and then soldering the lead lining plates to the whole steel surface. This technique eliminates the problem of buckling and blistering. It also means that in the event of failure of the lining only the steel directly behind the gap in the lining is attacked. In the so called  loose lining  technique in which the lead sheets are tacked to the shell  only along with seams  a failure at any point usually means that the corrosive contents of the vessel will shortly enter the entire space between the lining and the vessel wall. The spray drier feed tank may be lined in this fashion  but only moderate temperature are encountered in this tank and the agitation is never violent.

In general  the lead linings in the Igepon process equipment last 7 to 9 years before they must be replaced. The reaction kettles may be of stainless steel. If however  it is brick lined construction it may require re lining after about each two years. All equipment which comes in contact with finished liquid Igepon is made of stainless steel  since the detergent will exchange cations with ordinary steel to form iron salt which has an undesirable dark colour.

Submerged steam lines in the brick lined kettle are stainless steel  in the spray dryer feed tank these are lead. The other kettles are equipped with external jackets. Agitators are either lead covered  stainless steel  or in the case of the spray drier feed tank  wooden.

Neither stainless steel nor lead will stand up in the duct which carries the moist exhaust from the spray drier. Nickel or high nickel alloy serves well. The spray drier itself is made of carbon steel.

Tanks which must withstand static pressure such as those employing air pressure transfer are entered and inspected  and subjected to hydraulic testing every 2 years. Unpressurized steel tanks which store corrosive liquids are on a similar inspection schedule. Storage tanks in non corrosive service are inspected every 5 years. Kettles are also inspected at 5 years intervals. Jacketted kettles are lifted out of their jackets  and the surfaces are cleaned and inspected for pits. Pits usually occur in the welded seams. If the welds are badly pitted below the surface of the adjacent plates the bead is chipped off and the seam rewelded.

Since most of the materials involved in the process are transferred through the plant by air pressure  pumps present only a limited corrosion problem. Where pumps are used they are of motor driven centrifugal type. Where pure oleic acid must be pumped  a high alloy steel pump is used. All other pumps are of carbon steel.

Stainless steel valves are used on all lines which transfer finished liquid Igepon T. Pipe lines which carry liquid Igepon T also are of stainless steel. Those which transfer oleic acid chloride are lead lined and steam traced. The steam tracing is only used in the winter when the acid chloride has a tendency to thicken and move sluggishly.

Bleaching Agents

A bleaching agent may be defined as a compound  which is used to remove color from natural or artificial products and thus whiten them.

History

From earliest times until the end of the 18th century  the only known method of bleaching cloth was a process which required steeping the fabric in solutions of alkali derived from limestone  wood ashes  or kelp  followed by treatment with lactic acid from sour milk  and after rinsing  repeated exposure of the moist cloth to sunlight. Natural fibers contain certain oils  waxes  dirt  etc which can be completely or partially removed by the aqueous alkali. The action of sunlight  particularly ultraviolet radiation  activates the oxidation of the remaining colored substances to a colorless form or renders them soluble.

Bleaching of cloth by this method was not widely used until after the Renaissance when there was a demand from the masses for bleached cloth. Most of the material bleached was linen  since cotton was considered to be sufficiently white without bleaching and hemp  jute  and other fibers were too difficult to treat.

In the 18th century  the art of bleaching reached its greatest perfection near Haarlem  Holland. Linens woven in Britain and elsewhere were sent to Holland in the spring for bleaching and returned to the weavers in the fall for finishing and marketing. The method was established in Ireland by the middle of the century and improved by the use of dilute sulfuric acid instead of sour milk.

The obvious disadvantages of the method were the length of time required and the fact that the land used in this way was not available for essential farming.

In 1774  Carl Wilhelm Scheele discovered elemental chlorine and observed its bleaching effect on vegetable fibers. However  aqueous solutions of chlorine caused too much tendering of the cloth. The French chemist Berthollet found that chlorine could be absorbed in solutions of caustic potash or carbonate to give a satisfactory bleaching agent. Commercial production of these solutions was undertaken in Javelle  France and the potassium hydroxide product  called  eau de Javelle   was first applied to cloth in about 1786. Labarraque substituted caustic soda or soda ash for caustic potash  calling his product  eau de Labarraque.  Subsequent development of the LeBlanc process for soda ash made  eau de Labarraque  less expensive and it soon replaced  eau de Javelle .

In 1799 Charles Tennant  in Scotland  prepared bleaching powder from chlorine and slaked lime. The discovery of bleaching powder made possible for the first time a product which could be shipped in solid form from a chemical plant to a textile mill  thus eliminating the need for chlorine generating plants at each mill. Chemical bleaching then completely replaced the old bleach fields of England  Ireland  and Holland.

Bleaching powder remained the most important textile bleach until after World War I when tank cars were developed to ship liquid chlorine. It then became more economical to ship liquid chlorine and caustic to the mills to form liquid bleach at the point of use. However  tropical bleach  which is a more stable material produced by the addition of quick lime to bleaching powder  is still used in significant amounts in the underdeveloped areas of the world.

Hydrogen peroxide was prepared by Thenard in 1818 by reacting dilute sulfuric acid with barium peroxide. Peroxide had little or no use as a textile bleach during the 19th century. Electrolytic production of hydrogen peroxide  which began in 1908  reduced its cost. By the end of the 1920s  when strong solutions of about 30% hydrogen peroxide were available  peroxide was used extensively to bleach cotton goods. The adaptability of hydrogen peroxide to continuous bleaching operations started a mechanization trend in the industry. Hydrogen peroxide has now largely replaced sodium hypochlorite in the textile industry.

It is interesting to follow the parallel development of the bleaching of wood pulp. The ancient bleaching process was too lengthy and expensive for use on paper stock and the whiteness of paper depended upon the use of sorted white rags. While there is some disagreement as to the date of the first use of chlorine for bleaching rags and pulp  evidence exists that chlorine was being manufactured and used for this purpose by the Gilpin Paper Mills in Delaware by the summer of 1804.

In 1854  Watt and Burgess obtained U.S. Patent 11 343 for caustic pulping. Although the three stage process involving chlorination followed by alkaline extraction and hypochlorite bleaching was well known by 1875  the fact that liquid chlorine could not be transported or easily handled prevented any extensive use. Therefore  pulp was bleached mainly in a single stage process using bleaching powder. After tank cars for transporting liquid chlorine were developed during World War I  the three stage process began to be used for sulfite pulp  and with additional stages  was adaptable to bleaching Kraft pulp. Batch chlorinators eventually gave way to continuous chlorination. Nakoosa Edwards Paper Company first reported large scale chlorination of pulp in 1930 and 1932.

In an effort to obtain increased brightness with minimum degradation of pulp  other oxidizing agents were introduced. The development of sodium chlorite as a commercial bleach in the 1930s provided a chemical which could be used for a final brightening with little damage to the cellulose. The active agent in the process is chlorine dioxide  which can now be obtained more economically by using generators containing sodium chlorate  sulfuric acid  and a reducing agent such as sulfur dioxide  hydrochloric acid  or methanol. Other chemicals used experimentally for final brightening are sodium peroxide  perborates  percarbonates  peracetates  and ozone. The cost of these is often prohibitive.

Sodium chlorite is also an effective bleach for textiles and is used for both cotton and synthetic fibers. In addition to bleaching pulp  chlorine dioxide is used for the bleaching of flour and sugar and for upgrading inedible fats and oils.

Another important use of bleaches is in commercial and home laundries. Initially  bleaching powder was used. Sodium hypochlorite solutions and calcium hypochlorite have since replaced bleaching powder. The most recent products introduced for laundry use are mixtures containing chlorinated hydantoins and chlorinated isocyanuric acids. The latter are also active ingredients in cleanser formulations.

Certain reducing agents are used as bleaches. Sulfur dioxide had been used as a bleach since Roman times. It has several considerable disadvantages when applied to vegetable fibers  but can be employed to bleach wool with little damaging effect. Sulfur dioxide as well as thiourea and sodium dithionate are excellent antichlors to remove traces of chlorine or other oxidizing bleaches.

Mechanism of Bleaching

A successful bleaching process must remove colored impurities by converting them to colorless compounds and/or to compounds which are soluble.

In many cases  color in a molecule is attributed to the presence of conjugated double bonds  that is  a series of alternate single and double bonds  with atoms or groups at the end of the chain which can exist in two states of covalency  thus permitting resonance and resulting in color. Bleaching can be achieved by any agent which will disrupt the resonating structure  either by reaction with one of the conjugated double bonds or by oxidation or reduction of the group at the end of the chain.

Chlorine often bleaches by adding across double bonds or by oxidation  but at the same time causes undesirable tendering of fabric. Acidic chlorination is used as the first stage bleach in the preparation of wood pulp because of the high concentration of reactive impurities. At low pH values  te equilibrium below is shifted to the left and

Cl2 + H2O   HOCl + H+ + Cl–

chlorination of lignin is achieved together with some oxidation but without severe degradation of the cellulose since the concentration of hypochlorous acid is low.

Bleaching agents which furnish hypochlorous acid in solution will chlorohydrinate a double bond  adding an OH group on one side of the bond and a Cl on the other. The latter is usually hydrolyzed and replaced by an OH group fairly rapidly to form a 1 2 glycol. Peroxides form epoxides across double bonds. Under bleaching conditions  the epoxide is converted to a 1 2 glycol. In both cases the 1 2 glycol may be oxidized  breaking the single bond between the carbons to form two carboxylic groups.

Chlorine dioxide will not attack an isolated double bond. Although its bleaching ability depends upon an oxidation process and its use involves little or no damage to the fiber  the mechanism of its action has not been established.

Reducing agents can sometimes hydrogenate a double bond.

Hypochlorous acid and hypochlorites bleach colored organic compounds which contain no conjugated double bonds by chlorination to form a colorless product or by oxidation in which extensive breakdown of the molecule frequently occurs.

Generally  bleaching reactions are not reversible.

Bleaching is a complex process which cannot be fully explained or predicted. The succession of treatments used and the conditions employed in each step are determined empirically to produce the most favourable result.

Bleaching Strength

The strength of a bleaching agent is expressed in terms of  available chlorine  in the case of chlorine containing bleaches and  active oxygen  in the case of oxygen containing bleaches.

Available Chlorine. Available chlorine is defined as the measure of the oxidizing power of the chlorine present in the compound. It is expressed in terms of chlorine with a gram equivalent weight (geq wt) of 35.45.

In an oxidation process  the reactions of chlorine can be considered as follows 

It can be seen that in the case of hypochlorites  the chlorine present in the molecule has twice the oxidizing power of elemental chlorine  in chlorine dioxide the chlorine has five times the oxidizing power of elemental chlorine and in sodium chlorite the chlorine has four times the oxidizing power. Therefore  when the oxidizing power is calculated as chlorine in available chlorine determinations  the result will be greater than the actual% chlorine in the bleaching agent. For example  sodium hypochlorite contains 47.62% chlorine and 95.24% available chlorine. Chlorine dioxide contains 52.56% chlorine and 262.8% available chlorine.

The available chlorine contents of various chlorine containing bleaching agents are given in Table 1.

Other oxidizing agents may be analyzed by the available chlorine procedure and their oxidizing power expressed for purposes of comparison as% available chlorine. For example  hydrogen peroxide has the equivalent of 208% available chlorine.

Active Oxygen. Active oxygen is the measure of the oxidizing power of compounds  such as inorganic perborates  percarbonates  or peroxides  which release hydrogen peroxide in acid solutions. It is expressed in terms of oxygen (O) with a geq wt of 8.00.

The active oxygen contents of oxygen containing bleaches are given in Table 2.

Table 2  Active Oxygen Contents of Oxygen Containing Bleaches

Methods of Analysis

Bleaching formulations generally contain only one active bleaching agent. The analyst is therefore not concerned with a separation of bleaches but rather with the identification and assay of the single bleaching agent present.

Identification

An unknown bleach sample should first be analyzed for total chloride by the Mohr method. A second analysis should be done in which 8% hydrogen peroxide is added until the evolution of oxygen ceases  followed by the standard chloride determination. If the total chloride found in the second determination is greater than that in the first  a chlorine containing bleach is present. If the two chloride determinations are identical  an oxygen containing bleach is indicated.

In the case of chlorine containing bleaches  a positive test for calcium indicates calcium hypochlorite. Organic chlorine containing bleaches as well as calcium hypochlorite can often be identified by infrared spectroscopy using the potassium bromide pellet technique on the original sample. Dichlorodimethylhydantoin can be separated from a formulation  if desired  by virtue of its solubility in methylene chloride or chloroform. Trichloroisocyanuric acid is very insoluble in water (1.2 g/100 ml at 25ºC) and as a result may be separated from inorganic builders. Sodium and potassium salts of dichlorocyanuric acid can best be identified by infrared and/or emission spectroscopy.

Oxygen containing bleaches can be identified by infrared spectroscopy or elemental analysis. The presence of boron indicates perborates  a positive test for sulfur indicates persulfates.

Assay Methods

Chlorine Containing Bleaches

Chlorine containing bleaches are assayed by iodometric or iodimetric determination of the available chlorine. The methods for specific compounds are discussed.

Calcium Hypochlorite  Bleach Liquor  and Tropical Bleach. For these compounds  available chlorine is determined iodometrically by titration with standardized sodium thiosulfate solution of the iodine released by treatment with potassium iodide and acetic acid.

Procedure

Transfer 3.6 4.0 g of sample to a tared  glass stoppered weighing bottle and weigh to the nearest 0.1 mg. Place a dry powder funnel in the neck of a 500 ml volumetric flask containing about 100 ml of water. Carefully transfer the sample through the funnel into the flask and rinse the weighing bottle and funnel with a fine stream of water. Stopper the flask and swirl the solution until must of the sample has dissolved. Dilute to volume with water  stopper  and mix thoroughly. While shaking or swirling to keep any solids in suspension and to insure representative sampling  pipet a 25 ml aliquot into a 500 ml Erlenmeyer flask containing 125 150 ml of water. Add 2 g of potassium iodide crystals  mix  and add 8 ml of glacial acetic acid. Mix and titrate at once with standardized 0.1 N sodium thiosulfate solution to a pale yellow color. Add 2 ml of 0.5% starch indicator solution and continue the titration until the blue color just disappears.

Sodium Hypochlorite. A procedure similar to the one for calcium hypochlorite is used for the determination of available chlorine in sodium hypochlorite solution.

Procedure

Dilute a 10.00 ml sample to 1000 ml in a volumetric flask. Dissolve 2 3 g of potassium iodide crystals in 50 ml of water in a 250 ml Erlenmeyer flask. Add 10 ml of acetic acid  then pipet a 100 ml aliquot of sample into the solution  keeping the tip of the pipet beneath the surface of the solution until drained. Titrate at once with standardized 0.1 N sodium thiosulfate until the solution is a pale yellow color. Add 1 ml of 0.5% starch indicator solution and continue the titration until the blue color just disappears.

 

Dry Cleaning Agents

Drycleaning of garments is done in much the same manner as laundering  except  that organic solvents are used in place of water. As in laundering  detergents are added to the solvent to enhance its cleaning quality. Other solvent additives are used to give the textile the desired finish. This may be done merely to improve the  hand  or  drape  of the textile  or chemical additives may be used to achieve water repellency  insect repellency  or flame resistance.

Drycleaning washers are similar in construction to commercial laundry washers  but in drycleaning provision is made for clarifying the solvent for reuse. In laundering the used wash water is discarded  this cannot be done with the more expensive drycleaning solvents.

In the drycleaning system the solvent is continuously pumped through the washer and then through some type of filter designed to remove all suspended soil. Provision is also made for distillation of the solvent to free it from the solvent soluble soil.

The filters also contain activated carbon to absorb dissolved dye which would otherwise build up in the solvent.

Other chemical products used in small quantities by drycleaners are formulated to remove stains by local application to the affected area of the garment.

Only two classes of solvents have proved suitable for drycleaning  petroleum fractions and a few halogenated hydrocarbons. All other classes of solvents fail to meet the following eight major requirements of a drycleaning solvent.

          It must not weaken  dissolve  or shrink the ordinary textile fibers.

          It must not remove the common dyes from fibers.

          It must be an acceptable solvent for fat and oils.

          It must not impart an objectionable odor to drycleaned textiles.

          It must be sufficiently volatile to permit reclamation by distillation and to permit garments to be dried without prolonged heating at excessive temperatures.

          It must be noncorrosive to metals  either when dry or in the presence of water.

          It must be relatively nontoxic.

          It must have a flash point of 100° F or above.

The major drycleaning solvents used in the U.S. are the petroleum fraction called Stoddard solvent of which there are four types  perchloroethylene  and to a limited extent  trichlorethylene and trichlorotrifluoroethane.

With the exceptions of the solvents  the chemicals used in drycleaning are sold as brand name formulations  and the only tests performed on them are the determination of the amount of detergent in the solvent  and the amount of water in a solution of detergent in solvent. However  these chemicals are tested to determine how well they perform the function they are designed for according to a number of procedures developed by the National Institute of Drycleaning (NID).

Stoddard Solvent

Much of the drycleaning done in the United States employs a solvent  corresponding to a petroleum fraction with a minimum flash point of 100°C. This solvent has been named Stoddard solvent for W.J. Stoddard. The first commercial standard for a drycleaning solvent  CS3 28  was issued in 1928 by the National Bureau of Standards. The latest  revision of this specification is CS3 41  it also became an ASTM standard  D 484 52. Table 1 summarizes the current specifications of regular Stoddard solvent.

Today  three other petroleum fractions are also broadly termed as Stoddard solvents. These are the 140°F solvent  the low end point solvent  and the odorless solvent.

l40°F Solvent. This solvent is safer than the regular Stoddard solvent. Therefore  it may be used in locations where Stoddard solvent is prohibited. Also  building codes for plants using 140°F solvent are not so rigorous. For example  explosion proof motors and other electrical fixtures are not required. Plants using this solvent are designated Class 3 in the Handbook of the National Fire Protection Association.

Low End Point Solvent. This type of Stoddard solvent has a dry point in the range of 330 362°F  compared with 368 409°F for the regular Stoddard solvent. The result is a rapid drying solvent. There is no specification covering this solvent. It is regarded as a premium grade because of the fast drying feature.

Odorless Solvent. Whereas regular Stoddard solvent is specified to be free of objectionable odor  this new class of Stoddard solvent is free of all odor. This is achieved by removing or hydrogenating all aromatic compounds. The solvent also meets all requirements for a nonsmog producing solvent  since smog production is related to the aromatic content.

Odorless solvent is also regarded as a premium grade of Stoddard and is not covered by a separate specification.

Specification Tests

Some comments to the specification tests for Stoddard solvent are given here.

Odor. The term sweet as used in the specification means the opposite of rancid or sour. Although the usual methods of clarifying solvent in a drycleaning plant remove odors that accumulate during continued drycleaning  these processes do not always remove odors caused by improper refining. Therefore  the solvent  when received from the refinery  should be free from undesirable odor. There is nothing to show whether or not a solvent meets the requirement except the opinion of the examining chemist. Many samples of Stoddard solvent have a rather strong odor  but it is easily removed from the fabric by conventional drying methods.

Flash Point. The flash point is governed by those portions of the solvent that have the lowest boiling points and are therefore the most volatile. Since these portions evaporate more rapidly than the rest of the solvent  the flash point of Stoddard solvent in a drycleaning system gradually rises with use. Soaps  prespotters  or other added materials sometimes contain low flash solvents (such as some alcohols) that lower the flash point of the solvent and increase the fire hazard. The introduction of even small amounts of methyl  ethyl  or isopropyl alcohol into a washer lowers the flash point of the solvent below normal room temperatures.

A lighted match  held over Stoddard solvent at ordinary room temperatures  does not ignite the solvent because the solvent is not giving off enough vapor to form a combustible mixture with the air. If the temperature of the solvent is raised  vapor pressure is increased  and the air above the solvent becomes richer in solvent vapors. Finally  a temperature is reached where enough solvent has vaporized to form a combustible mixture with the air. If a flame is then introduced above the solvent  the vapors will flash. The lowest temperature at which this occurs is called the flash point. Since the flash point of Stoddard solvent may not be under 100°F  there is no danger of fire from solvent vapors until the temperature of the solvent rises to 100°F or above.

The flash point specification is frequently violated. In some cases  the refinery may have set the lower limit of the distillation range too low. Such violations usually result in a solvent with a flash point of 98 or 99°F. A more dangerous type of violation  however  results from careless handling of the solvent. For example  Stoddard is sometimes transported in tank trucks that were previously used for carrying gasoline and still contain small qnantities of gasoline. As little as 1% of gasoline in Stoddard solvent lowers its flash point  considerably.

The flash point is determined by ASTM D 56 64 method.

Corrosive Properties. Improperly refined solvent may contain traces of dissolved free sulfur  which can corrode the metals of storage tanks and equipment. The corrosion test is carried out according to ASTM D 1616 60  at  an elevated temperature  121°F. Under these conditions  corrosion that would be apparent after considerable use of the solvent at room temperature can be seen after only 3 hr.

Distillation Range. From the standpoint of a drycleaning solvent  there are disadvantages in products containing very low or very high boiling hydrocarbons. Low boiling hydrocarbons  petroleum ether and gasoline  cause fires and high evaporation loss  high boiling hydrocarbons  such as kerosene  cause excessive drying time. The distillation range for Stoddard solvent is between 300 and 410°F  a range not low enough to cause undue fire hazard and evaporation loss  or high enough to prolong the drying time.

The distillation range of Stoddard solvent is determined according to ASTM D 86 66 and D 1078 67.

Residue. Excessive nonvolatile matter in the solvent often contributes to odors and lengthens drying time. Because of the high temperatures used  a small amount of odorous residue is usually formed during the distillation test. A sample of the same solvent evaporated on a steam bath  where temperature is not raised above 212°F  yields a smaller and less odorous residue. The residue of Stoddard solvent is determined according to ASTM D 1078 67.

Acidity. If the solvent is given a sulfuric acid treatment in the refinery and not followed by a neutralizing treatment (such as with caustic soda)  it will contain small amounts of sulfuric acid or other acidic materials. Even small amounts of sulfuric acid are undesirable in a drycleaning solvent  as they corrode equipment and damage garments. Fortunately  almost without exception  drycleaning solvents pass the acidity test.

Sulfuric acid has a very high boiling point . The presence of this substance in the solvent will be as residue in the flask after the distillation. If a residue of 1 ml remains from distilling 100 ml of solvent  any sulfuric acid present is concentrated there 100 times. Thus  it  is logical to test the residue from distillation for sulfuric acid.

According to ASTM D 1093 65  the solvent sample is shaken with water and one drop of a 0.1 % methyl orange indicator solution is added to the aqueous layer  there should be no change in the color of the indicator.

Doctor Test. Mercaptans impart to the solvent unpleasant odors  which may be absorbed onto the garments during drycleaning. The doctor test is a qualitative method to determine whether the treatment for mercaptans was properly done in the refinery. Sulfur and sodium plumbite are added to the solvent in a test tube. If mercaptans are present in the solvent  the reaction proceeds and the black lead sulfide formed is indicative of a positive test.

2 RSH + S + Na2PbO2 ® R2S2 + PbS + 2 NaOH

Sulfuric Acid Absorption Test. This test determines if the solvent contains appreciable amounts of unsaturated hydrocarbons. These would be in the solvent if it was inadequately treated with sulfuric acid during refining. Since unsaturated hydrocarbons turn rancid and cause undesirable odors in drycleaned garments  it is imperative that they be removed before the solvent leaves the refinery.

In the test concentrated sulfuric acid is added in a graduated cylinder to the solvent and shaken. Sulfuric acid reacts with any unsaturated hydrocarbons present  and most of the products of the reaction settle into the acid layer  thus the volume of the solvent is decreased. Since some of the products formed from the reaction remain in the solvent layer  the test does not give a quantitative measure of unsaturated hydrocarbons  that is  a 5% absorption of the solvent by sulfuric acid actually represents a greater percentage of unsaturated hydrocarbons in the solvent.

Variations in the strength of commercially available concentrated sulfuric acid  cause variations in the sulfuric acid absorption test. Therefore  the acid strength must be standardized if reproducibility is desired.

Perchloroethylene

Perchloroethylene (tetrachloroethylene) became an important drycleaning solvent because of its nonflammability  which permits its use in places where all types of flammable solvent are either forbidden by codes or inhibited by high insurance rates. Its general properties are given in Table 3  and the specifications proposed by the NID are listed in Table 4.

Table 3  Properties of Perchlorethylene

Specification Tests

The following specification tests were developed by the NID.

Residual Odor. Any residual odor left in a fabric after treatment in the solvent is objectionable. Detection of such odors by smelling is more sensitive if the fabric is steamed immediately prior to the test. A swatch of bleached but unfinished cotton poplin  Style A 400W  Testfabrics  Inc.  is used and subjected to the following test.

Procedure

Condition the cotton at 60% relative humidity for at least 8 hr prior to use.  Soak the swatch in perchloroethylene for 5 min  then remove it and hang it to drain dry for about 4 hr. Tumble the swatch in a tumble dryer for 30 min at 140°F.

To test for odor  grasp the swatch in the center with a forceps  hold it in live steam for 5 sec  and smell it immediately. Test an untreated swatch simultaneously. There should be no discernible difference in odor between the two swatches.

Nonvolatile Residue. This test detects the presence of nonvolatile impurities in the solvent. It is determined gravimetrically by evaporating a measured quantity of solvent and weighing the residue as follows.

Procedure

Dry a 4 in. diameter evaporating dish and weigh it to the nearest 0.1 mg. Place it on a steam bath in a hood and add the perchloroethylene to be tested by pipet in two 50 ml portions. Perchloroethylene has a high specific gravity  1.62  and is difficult to handle in a 100 ml pipet. Add the second portion after the first is partially evaporated.

After the solvent has completely evaporated on the steam bath  heat the dish further in an oven at 105°C for 1 hr  then cool it in a desiccator and weigh. The increase in weight of the dish in grams for a 100 ml sample is % nonvolatile residue.

Stability Test. Perchloroethylene is stabilized by adding traces of chemicals known to inhibit its decomposition. Loss of stabilizer or the presence of certain impurities can lower the stability of the solvent.

Procedure

Wash two strips of copper foil  2.0 X 7.5 X 0.005 cm  in concentrated hydrochloric acid. Rinse  dry  and weigh to the nearest 0.1 mg. Add 75 ml of the test solvent and 3 ml of water to a 300 ml Soxhlet extractor. Place one copper strip in the flask and the other into the condenser of the Soxhlet. Heat the Soxhlet at a rate that will cause it to empty every 8 10 min.

After 24 hr  remove the strips  wash them again in concentrated hydrochloric acid  and weigh. The combined weight loss of the two strips should not exceed 30 mg.

Note  Do not fail to add the water with the solvent. The test is worthless in the absence of water.

Fluorocarbon Solvent

Around 1960  Du Pont introduced trichlorotrifluoroethane as a drycleaning solvent under the trade name Valclene. This solvent has aroused much interest because of its ideal properties  but it is too volatile to be used in machines designed for perchloroethylene. Therefore  its full utilization must a wait machine development. A number of companies have introduced small machines for the solvent  but it will be several years  before use of the solvent is widespread.

No special specifications or test methods have been developed for this solvent.

Used Drycleaning Solvents

In addition to the tests given under the specifications  there are several analytical methods designed for quality control purposes in practical drycleaning operations. These methods are normally performed on used solvent taken from plant washers. The following tests are made routinely on used solvent.

Detergent Concentration. The method of Fessler for anionic detergents is used. It is described on. There is no satisfactory method for drycleaning detergents that are all nonionic  however  manufacturers of nonionic detergent formulations normally include some anionie surfactant in the mixture to serve as a tracer. This serves the purpose of quality control with a known product but not for analysis of an unknown mixture.

Nonvolatile Residue. This test is carried out by the procedure except that 10 ml samples are used instead of 100 ml

Moisture Content. The moisture content of the used solvent can be determined by the Karl Fischer method.

Acid Number. This test was originally designed to measure the buildup of fatty acids in the solvent. Its value has diminished in recent years because of the widespread use of amine sulfonate detergents. These detergents react quantitatively with the titrant giving a high value for the fatty acid content of the solvent. However  the test is still useful for control purposes where proper correction can be applied for interference by the detergent.

In other fields  acid number is defined as the mg of potassium hydroxide necessary to neutralize 1 g of sample. In drycleaning  the NID has defined acid number as the mg of potassium hydroxide necessary to neutralize 1.28 ml of solvent.

The titration is made in the usual manner using a 0.06 N alcoholic solution of potassium hydroxide and phenolphthalein indicator. It was found that 2 methyl 2 4 pentanediol is a better solvent than ethanol because of its solubility in petroleum solvents.

Color. The color of used drycleaning solvents may be due chiefly to dyes dissolved from the textiles. The balance is caused by colored soils  or colloidally suspended pigments. The latter are removed by micro filtration prior to determining color. At NID  color is determined on a Coleman universal spectrophotometer using a 40 mm cuvet at 500 nm. The instrument is standardized against water.

Greying of Cotton. The cotton fabric used for the residual odor test is read on the reflectometer to determine the decrease in % green reflectance. Although this is called  greying  it is actually a measure of the amount of dye and other colored impurities dissolved in the solvent because the insoluble material has been removed by microfiltration through 0.2 µm membranes.

Sizing. Many drycleaners use certain resins in the solvent as sizes or bodying agents for fabrics to replace the finishing materials removed during wear or cleaning. Natural terpene resins are widely used and the amount of resin in the solvent is determined at NID by extracting the nonvolatile residue with boiling ethanol. This reagent dissolves everything except the terpene resins. The procedure has not been validated  however  for all types of sizes.

Suspended Solids. After microfiltration of a measured volume of the solvent  the membrane  which has been previously weighed  is oven dried at 105ºC and weighed to determine the quantity of insoluble material suspended in the solvent. The NID standard for this is 50 mg/liter. Larger quantities can cause excessive greying of white fabrics and is an indication of poor solvent filtration.

Drycleaning Detergents

Detergency in nonaqueous solvents follows much the same principles as in water  particularly in the removal of insoluble soil. The major differences come in the attack on water soluble and solvent soluble soils. In aqueous detergency the major attack is on the oily soils because the water soluble soils are removed by simple solution. In drycleaning  on the other hand  the major attack by detergents is on the water soluble soil because the oily soil is removed by simple solution.

In both laundering and drycleaning  the processes of emulsification and solubilization effect the removal of soil from the fiber surface. In both types of cleaning the detergents used are based on surface active agents.

Laundry detergents generally contain not  more than 20% surface active agents (surfactants)  the balance being various types of builders. Drycleaning detergents may consist of a single surfactant. The product may also contain a cosolvent or coupling agent to enhance the capacity for dissolving or emulsifying water and a fluorescent whitening agent. Frequently  two or more surfactants are mixed.

A drycleaning detergent performs three functions in the cleaning process. It acts as a dispersant or peptizing agent for insoluble soils. It not only disperses this kind of soil  but also keeps it in suspension. While it is being flushed out of the fabric and pumped to the filter. Insoluble soils may be dispersed to particle sizes in the submicron range by good detergents  and while so dispersed the particles of soil are small enough to escape between the tightly packed fibers in textile yarns. In the absence of a good detergent  this kind of soil is difficult to remove and readily redeposits on other fiber surfaces causing what is generally called greying  a phenomenon also common in laundering  particularly with polyester fibers. Thus  the first two roles of a drycleaning detergent are to assist in the removal of insoluble soil and to prevent it from redepositing on other fabrics in the bath.

The third function of a drycleaning detergent is to emulsify water in the solvent and promote the removal of water soluble soil by the emulsified or solubilized water. Although the water plays the major role in detaching water soluble soil from the fiber surface  the detergent itself can dissolve some of these soils within its micelles.

Progress in the formulation of drycleaning detergents is slow compared to the formulation of laundry detergents. One reason for the lack of progress has been the absence of reliable test  methods for drycleaning detergents. The literature on drycleaning detergent test methods is scanty and the few methods that have been described have received little attention or use. The methods described here have been in use at the National Institute of Drycleaning and are designed to test the ability of a detergent to perform its three functions.

Methods of Analysis

The tests to be carried out on drycleaning detergents can be divided into two groups  specification tests resulting in information on the properties of the detergents  and performance tests.

Specification Tests

Physical Composition. Drycleaning detergents  almost without exception  are liquids  so it is desirable to know how much of the material consists of an active ingredient and how much is solvent or water. The determination is made on a perchloroethylene solution of known concentration of the detergent. An aliquot is evaporated to dryness as described on p. 608 for the determination of the nonvolatile residue of a solvent. The amount of water is determined on a separate sample by the Karl Fischer titration.

Some drycleaning detergents are diluted with mineral oil so that the nonvolatile residue is not all surfactant  but it still establishes the upper limit of surfactant concentration.

Specific Gravity. The main purpose of this test is to establish what types of solvents are used as diluents. Most surfactants have specific gravities close to unity  whereas drycleaning solvents have a specific gravity of about 0.8 (Stoddard solvent) or 1.62 (perchloroethylene). The determination can be carried out by any of the conventional methods.

pH. A drycleaning detergent should be essentially neutral because of the adverse effect of acids and alkalis on some types of dyes. The test is made by thoroughly shaking the detergent with water and determining the pH of the water phase.

Distillation Test. Since used drycleaning solvent is reclaimed by distillation  it is important that the detergent cause no problems in the still. This is checked qualitatively by distilling a 1% solution of the detergent in perchloroethylene in an all glass laboratory still. The process is observed for any signs of foaming  flooding over  or decomposition. The distillate should be pure perchloroethylene  presence of other volatile solvents is undesirable.

Detergents intended for use in Stoddard solvent must be tested by vaccum distilling a 1% solution in this solvent.

Solubility in Drycleaning Solvents. The purpose of this test is to ascertain that the detergent is soluble in both solvents. A simple qualitative test is sufficient.

Chemical Type. It is desirable to know whether the surfactant in the detergent is anionic  cationic  nonionic  or a mixture of ionic and nonionic surfactants. This can be determined by studying the infrared spectrum of the sample as well as the methylene blue titration method given below.

Detergent Concentration by Methylene Blue Titration. This method is widely used as a control test to determine the amount of a particular detergent in a drycleaning solution. It was originally described by Fessler  in 1951. The following procedure is from an NID publication.

Procedure

Anionic Surfactants. Place 25 ml of chloroform into a 100 ml glass stoppered graduated cylinder. Take at least a 5 ml sample of the solution to be tested  dilute to 100 ml  and then add a proper .aliquot to the chloroform. Add 25 ml of water containing 1 drop of a 0.5% methylene blue solution and shake. The methylene blue enters the chloroform layer as a result of solubilization by the surfactants. Start to add a 0.02% aqueous cetylpyridinium chloride solution in 0.5 ml increments and shake the mixture vigorously after each addtion. As long as any free anionic surfactant remains in the chloroform layer. Eventually this is complete and the lower layer is colorless. A sharp and reproducible end point is the point of equal color distribution between the two phases. Prepare a calibration curve for each detergent by titrating a number of samples of known volume volume concentration over the expected range and plotting ml of titrant against detergent concentration.

Cationic Surfactants. Carry out the determination in a similar way but by using a standard anionic surfactant such as Aersol OT as the titrant.

Nonionic surfactants cannot be titrated in this manner. However  detergents consisting of nonionic surfactants generally contain a small amount of anionic surfactant  as a tracer so the solution can be titrated to control concentration.

Acid Number. One of the most widely used types of drycleaning detergents is classified as amine sulfonate. When solutions of amine sulfonates are titrated by alcoholic potassium hydroxide as in the usual acid number determination they hydrolyze and the sulfonic acid titrates as if it were a fatty acid. Thus  this titration gives information of the relative quantities of this type of surfactant present.

If the composition of the detergent  is known to be amine sulfonate  this determination provides a more rapid and convenient method of analysis than the methylen blue titration.

Water Holding Capacity. This is the most important specification test to be made on drycleaning detergents because performance tests cannot be carried out without this information.

To understand the method  it is necessary to know something of the moisture relations in a drycleaning bath between a detergent solution  a textile immersed in it  and the atmosphere in equilibrium with the solvent phase. Briefly  the solution dissolves water within the detergent micelles which retard evaporation and lower the water vapor pressure over the solution. Eventually  the solution comes to moisture equilibrium with the immersed textile and the atmosphere over the solution. At equilibrium  the water vapor pressure in all three phases must be equal. If the relative humidity in the vapor phase is 75% then the solution is said to have a solvent relative humidity of 75%. At this condition the immersed textile will have the same regain or absorbed moisture content as it would have at equilibrium in the vapor phase at 75% relative humidity.

The NID defines the water holding capacity as % water in a 1% detergent solution measured at a solvent relative humidity of 75%.

The amount of water in both the solvent and textile is determined by a Karl Fischer titration whereas the relative humidity of the vapor phase is measured with Dunmore type humidity sensors.

It is the usual practice to determine the moisture content of a series of 1% solutions of the detergent at various solvent relative humidity values  and to plot the data to obtain a moisture content vs relative humidity curve for the detergent. The curve permits the estimation of the solvent relative humidity of any solution of that detergent by a Karl Fischer titration (giving the amount of water) plus a methylene blue titration (giving the amount of detergent). It should be noted that the solvent relative humidity depends only on the ratio of water to detergent in the solution. Hence if a 1% solution of a particular detergent contains 0.07% water at 75% relative humidity  then a 2% solution will contain 0.14% water at the same relative humidity.

Light Transmittance. This value is an index of the degree of clarity of a 1% (v/v) solution of the detergent. The transmittance is normally measured at 450 and 500 nm  the most sensitive region for yellow or amber colored products.

In some cases  the color is due to solubilized impurities such as iron oxide  which can deposit on fabrics. The solution is tested for this possibility by immersing a white cotton fabric of about 94% reflectance  green filter  into the solution. After removal and air drying  the reflectance is again measured. A loss of reflectance of more than 4% (i.e.  a reflectance below 90%) is considered excessive.

Performance Tests

Two performance tests are usually carried out  a test for insoluble soil removal and redeposition control  and a test for water soluble soil removal.

Insoluble Soil Removal and Redeposition Control. The ability of a drycleaning detergent to remove insoluble soil and to prevent that soil from redeposition on another fabric is tested by adding soiled and unsoiled swatches of cotton fabric to a test solution of the detergent in a Launder Ometer or in aTerg O Tometer. These are machines with thermostatically controlled water baths and oscillating type agitators. The Terg O  Tometer has an oscillating agitator but the Launder Ometer uses rotating canisters. They may be purchased from the following companies  (a) Launder Ometer  Atlas Electric Devices  4114 N. Ravenswood Ave.  Chicago  Ill.  (b) Terg O Tometer  U.S. Testing Co.  1414 Park Ave.  Hoboken  N.J. The reflectance of the cotton swatches is taken before and after the cleaning operation  and the detergent formulations are rated with a reference detergent having only mediocre cleaning ability. The reference detergent is Aerosol OT  sodium di(ethylhexyl) sulfosuccinate  long used as a standard detergent in drycleaning research because of its chemical purity  it is available in 99+% active grade. Test conditions deliberately overwhelm the reference detergent so that the superiority of the test detergents will be readily manifested.

The insoluble soiling material is applied to the test swatches so that the particles are fully dispersed. If this is not done  reflectance measurements are not accurate. If wet soiling methods are used  a dispersing agent is used and subsequently rinsed out  or the pigment material is mechanically dispersed in oil with a mortar and pestle or ball mill. Before testing  the soiled and unsoiled swatches are conditioned at 75% relative humidity for several days at 70±5°F. A desiccator over a saturated sodium chloride solution may be used or the test can be standardized on the basis of 65% relative humidity and 70°F  the standard textile testing laboratory conditions  in a constant temperature humidity room.

Aerosol OT is slow to dissolve in drycleaning solvent  so a stock solution of known concentration should be prepared and aliquots taken and diluted to 1% for use in the test. Solvent used in the test should be prefiltered through a 0.2 µm Millipore filter.

Procedure

Determine the reflectance of all 4 X 4 in. swatches  using the green filter. Use the blue filter also if yellowness changes are desired. Run all tests in duplicate using a Launder Ometer equipped with 500 ml stainless steel canister. Add 150 ml of the detergent solutions to each canister  then add thirty ¼ in. stainless steel balls.

Use three clean and three soiled swatches for each canister. Add clean and soiled swatches alternately  crumpling each slightly to prevent them from adhering and to improve the agreement of the replicates.

Run the Launder Ometer for 1 hr at 25±1°C to reach equilibrium.

Empty the canisters into 10 cm diameter Buchner funnels to drain away solvent. With forceps take each swatch by a corner and dip it rapidly ten times into two successive rinse baths of 300 ml of filtered perchloroethylene. Use clean rinse solvent in both beakers for each canister.

Lay the rinsed swatches on a blotter paper  cover them with another blotter paper  and dry overnight at room temperature.

Read the reflectances of each swatch as before and calculate the averages for each detergent. Compute the average change in reflectance of both the soiled and unsoiled swatches for each detergent being tested and for the reference detergent.

The ratio of reflectance change (DR) for each detergent to that of the reference detergent gives an index number permitting comparison of test data made at different time or under slightly different conditions.

The ratio of the unsoiled swatch reflectance changes is called the greying index and that of the soiled fabrics is the cleaning index. The lower the greying index and the higher the cleaning index  the better the detergent.

The most critical operations of this test are the reflectance readings  the addition of swatches  and rinsing.

Reflectance readings can vary with the instrument and the fabric construction. With the 45/0 geometry of the Gardner Precision reflectometer  twelve thicknesses of new cloth  or six of soiled  are sufficient to exclude the background. Big differences could affect readings through one thickness  so each subgroup should be kept together and rotated only within itself. Thus  for each set of two canisters  the twelve swatches are placed in a pack and rotated so that each swatch is always backed by eleven others. The five swatches immediately behind the one being read must be similar to it  that is  the six redeposition swatches have to be kept together. Readings of warp vertical and warp horizontal from both front and back must be averaged with this instrument. Instruments with spherical optics require only one reading on each side.

If the swatches are added alternately  one clean and one soiled  both the redeposition and cleaned groups will show little variation within themselves or between canisters.

Rinsing is only meant to remove the large  loosely attached particles. Quick motions and rinsing each swatch separately leaves very little if any on the swatches.

Several specifications in the procedure are not critical. For example  the moisture content is not a particularly sensitive variable in this test. However  it is sound test practice to control this variable if possible. The 1 hr running time is another arbitrarily fixed variable. This time was selected to give the samples every chance to equilibrate. A powerful detergent can bring the system to equilibrium earlier  equilibrium exists when all six swatches show the same reflectance. If a Terg O Tometer is used  the running time should be shorter  only 30 min  because of the greater mechanical action in this instrument. Also  evaporation losses may be serious from the open beaker of the Terg O Tometer in 1 hr.

The purpose of the yellowness measurement is to detect any effect due to an optical brightener in the formulation.

Under these test conditions  some soil will also redeposit on the soiled swatches. If it is desired to measure the specific soil removal  independently of greying  a much higher solvent volume needs to be used to minimize soil redeposition.

The procedure detailed above can be adapted to any type of standard soiled fabric suitable for use in a drycleaning solvent and soiled with a formula containing a high percentage of insoluble soil.

The NID has arbitrarily chosen to test detergents at the 1% (v/v) concentration level because this is the most frequently used concentration in drycleaning plants. Some products perform about as well at 0.25% as at higher concentrations  others require concentrations higher than 1% to exhibit their best performance. The test procedure is adaptable for studying concentration  solvent relative humidity  and other factors that are fixed in the procedure.

Water Soluble Soil Removal. The NID has long used rayon fabrics impregnated with sodium chloride or with glucose to measure water soluble soil removal in a drycleaning machine. These model soils are satisfactory for large scale tests but difficult to reduce to a laboratory scale due to moisture exchange between detergent solution  rayon  and salt or glucose. They will interact until three way equilibrium in water vapor pressure is reached. If the solvent relative humidity drops to 65% or below  little or no salt or glucose can be removed. The equilibrium can be controlled at a higher relative humidity level in a machine without difficulty  but not in small scale laboratory tests unless the test work is done in a constant temperature and humidity room. Not only will the fabric absorb moisture from the solvent  lowering its relative humidity  but the salt or glucose on the fabrics will absorb moisture. Salt is particularly trouble some because it does not attain equilibrium quickly with dissolved moisture but continues to pick up water until each crystal is surrounded by a droplet of liquid water.

The method used at NID and described below avoids the problem by using a polyester fabric that does not absorb moisture  and a water soluble dye as a model soil. The amount of dye on the fabric is so small that it  cannot remove a measurable quantity of water from the solution.

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