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:

          1.          Increase in viscosity during sulphonation thus necessitating efficient mixing.

          2.          Side reactions affecting yields

          3.          Poor bio-degradability

          4.          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

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.

2. 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%.

3. 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.

4. Sulphonation Using SO3 Gas from Oleum

(a) 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:

          (i)          The smaller size of equipment for the same throughput,

          (ii)          Reduction in spent acid production and

          (iii)          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:

          (i)          The use of a sulphuric acid scrubber

          (ii)          Compression, cooling and silica drying of air and

          (iii)          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.

(b) 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.

(c) 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%.

5. 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.

6. 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 :

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

          (2)   Products of reaction of one mole of a dialkylolamine with one mole of fatty acid.

          (3)   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:

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

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

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

          (d)   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?

          (e)    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?

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

          (g)  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.

R-COOH + H2NXOH — RCONHXOH + H2O

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: