It has been said that amount of soap and detergent consumed in a country is a reliable measure of its civilizations. There was a time when these products were luxury; now it is a necessity. A disinfectant or agent that frees from infection is ordinarily a chemical agent which kills disease germs or other harmful microorganisms and is applied to inanimate objects.
The present book contains formulae, processes of different types of soaps, detergents and disinfectants. These products have good demand in domestic as well as in International market. So there is a very good scope for new entrepreneurs to venture into this field.
This book is very useful for entrepreneurs, technocrats and for those who want to diversify in to this field.
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.â€
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 yâ€, respectively. The fraction
of
kettle was will then be equal to yyâ€/y’yâ€, and the fraction of lye will
be
equal to yy’/y’yâ€.
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 “settledâ€
soap
are termed “changesâ€.
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
“spentâ€
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 “finishingâ€. 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 zâ€
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 “washesâ€.
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:
        Â
1.        Â
Increase in viscosity during
sulphonation thus necessitating efficient mixing.
        Â
2.        Â
Side reactions affecting yields
        Â
3.        Â
Poor bio-degradability
        Â
4.        Â
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:
        Â
(i)Â Â Â Â Â Â Â Â Â
The smaller size of equipment for the
same throughput,
        Â
(ii)Â Â Â Â Â Â Â Â Â
Reduction in spent acid production and
        Â
(iii)Â Â Â Â Â Â Â Â Â
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:
        Â
(i)Â Â Â Â Â Â Â Â Â
The use of a sulphuric acid scrubber
        Â
(ii)Â Â Â Â Â Â Â Â Â
Compression, cooling and silica drying
of air and
        Â
(iii)Â Â Â Â Â Â Â Â Â
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 :
        Â
(1)Â Products
from the reaction of one mole
of a monoalkylolamine and one mole of fatty acid.
        Â
(2)Â Â Products
of reaction of one mole of a
dialkylolamine with one mole of fatty acid.
        Â
(3)Â Â 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:
        Â
(a) Does the
additive have the desired
foam boosting properties when added at the desired economic level?
        Â
(b)Â Are
the raw materials available at a
reasonable and stable price?
        Â
(c)Â Â Can
the additive be made consistently
or does it suffer batch to-batch variation which impairs its properties.
        Â
(d)Â Â 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?
        Â
(e)Â Â Â
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?
        Â
(f)Â Â Â
Is it stable under long-term storage
conditions or will it turn rancid or affect the perfume in anyway?
        Â
(g)Â 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.CSO3NaÂ
RCONH C2H4.CSO3Na
In this process however,
small amount of the ester
RCOOC2H4N5 is also formed which detracts activity. Other acids like
palmitic
solids, oleic and palm oil may also be used.
The manufacture of
alkylolamides is carried out in a
stainless steel factor fitted with an agitator and a thermocouple. The
reactor
is jacketted for steam, electric or oil heating. The process of
manufacture is
briefly outlined below.
Coconut Fatty Acid Diethanolamide
It is a yellow viscous
liquid, which finds
application as a foam booster in the manufacture of detergents and
shampoos and
also as an emulsifier and a solubilizing agent. Its composition is
usually,
60-70 per cent amide; 1 percent water; and 7 percent ester. pH of 1
percent
solution of this compound is 8 to 9. Its manufacturing process is as
follows:
Charge the reactor with 60
kgs. coconut fatty acid
and 63 kgs. diethanolamine. Switch on the heaters and regulate the
speed of
stirrer to maximum so as to mix the reactants properly. When the
temperature
reaches 130°C, pass nitrogen gas in the reaction mixture. See that the
reaction
mixture is thermostatically adjusted to 165ºC. As the reaction
progresses, the
acid value of the product falls down which is to be determined every
half an
hour interval. The reaction is stopped when acid value falls to 5.
Lauric Acid Diethanolamide
Lauric acid diethanolamide is
a white waxy material
having the composition—amide, 90 per cent; water 0.5 per cent; ester
5-6 per
cent; and free amine 1.2 to 3.0 per cent. It is used as a foam
stabilizer, as a
superlatting and thickening agent in the manufacture of shampoos and
detergents, and as a perfume fortifier in soaps. It is prepared as
follows:
Charge reactor with 60 kgs.
lauric acid and 63 kgs.
diethanolamide. Switch on the heaters. When temperature reaches 50°C,
allow
nitrogen gas to flow in reactor. Carry out the reaction at 170°C till
the acid
value drops to 5.
Oleic Acid Monoethanolamide
It is in amber coloured
viscous liquid soluble in
naphtha and kerosene. Its composition in 85 per cent amide, 1 per cent
water
and 7-8 per cent ester. It is used as a foam stabilizer and as a
superfatting
and thickening agent for shampoos and detergents. It is prepared as
follows:
Charge reactor with 84 kgs.
double distilled oleic
acid and 18 kgs. of monoethanolamine. Switch on the heater and stirrer.
When
the temperature reaches 120°C, allow nitrogen gas to bubble in reaction
mixture. Adjust temperature to 170°C. Check acid value of the product
every
half-an-hour till it drops to 5.
Stearic Acid Monoethanolamide
It is a cream coloured waxy
product having the
composition amide 90 per cent, ester 5 per cent, water 10 per cent and
amine
2-3 per cent. It is incorporated in toilet soaps and detergent cakes
for foam
stability and viscosity. It is prepared as follow:
Charge the reactor with 85
kgs. stearic acid and 18
kgs. monoethanolamine. Raise the temperature to 100°C and bubble
nitrogen gas
in the reaction mixture. Adjust temperature to l70ºC and check acid
value of
the product every half-an-hour till it falls to 5.
In addition to the methods
described above there are
several other processes available for the manufacture of these and
other
alkylolamides. The first alkylolamides were prepared about forty years
ago. The
first patents for preparing alkylolamides were granted to W.
Kritchevsky (See
U.S. Patents, 2,089, 212, and 2,096, 749) in 1937. They covered the
condensation of fatty acids, their triglycerides, esters, amides,
anhydrides
and halides with not substantially less than two moles of an
alkylolamine. The
reaction was carried out at 100 to 300ºC, below the decomposition of
the
resulting product and at atmospheric pressure.
An improved process for
making alkylolamides was
revealed in a 1949 patent (U.S. Patent 2,464,094) to Edwin M. Meade.
This
process comprised mixing an ester of an aromatic or aliphatic
carboxylic acid
with an alkylolamine, adding an alkali metal alkoxide catalyst and
heating the
mixture to 100ºC at atmospheric or above atmospheric pressures.
In 1958, Giuliana C. Tesoro
patented a refinement of
the Meade process (see U.S. Patent, 2,844,609). It consisted of
reacting a
fatty acid ester or glyceride with a primary or a secondary
alkylolamine in the
presence of a sodium methoxide catalyst at a temperature between 55 and
75°C
and under a reduced pressure of 40 to 60 mm of mercury.
A continuous process for
making fatty alkylolamides
in a thin film reactor is covered in a 1958 patent (U.S. Patent
2.863,888)
issued to Jack W. Schurman. The reaction involved condensation of a
methyl
ester of a fatty acid with a mono or dialkanolamine, in the presence of
an
alkali metal, alkali metal alkoxide, or alkali metal amide catalyst. A
short
contact time in the reactor produces a high purity alkylolamide.
More recently (1962) Robert
Ernest has patented
(U.S. Patent 3,024,260) another process for making high purity
alkanolamides. A
fatty acid is first reacted with an excess of alkylolamine, forming
amine and
amide esters in addition to the intended unsubstituted alkylolamide. In
a
second step involving an alkali metal catalyst, the amine and amide
esters are
converted to the unsubstituted alkylolamide.
John W. Lohr was also granted
a patent (U.S. Patent
3,040, 075) in 1962 for a process of making high purity alkylolamide by
condensing a dialklyolamine with a fatty triglyceride, then adding
phosphoric
acid to remove the excess a mine and most of the glycerine byproduct.
There are two types of
alkanolamide
products—Kritchevsky types liquid product and the super ‘amide’
product. The
first is made by reacting an alkylolamine with a fatty acid or fatty
acid
derivatives at elevated temperatures in a 2:1 ratio. Such a product
contains
60-70 per cent alkylolamide, plus some amine esters and diesters, and
piperazine derivatives that are formed by side reactions. In addition,
there is
significant unreacted alkylolamine. This excess alkylolamine renders
the
Kritchevsky type alkylolamines water soluble.
The second type of
alkylolamide is prepared by
reacting an alkylolamine and a fatty acid ester in a 1:1 ratio. These
are
generally solid products which have an alkylolamide content above 90
per cent.
Some of the same by-products formed in preparing 2:1 alkylolamides are
likewise
formed in preparing super amides, but in much smaller quantities. For
this
reason and because they contain only relatively small amounts of free
alkylolamine, super amides have poor water solubility. They are
therefore
always used in conjunction with a small amount of anionic or non-ionic
surfactant, which act as a solubilizer, converting an aqueous
alkylolamide
despersion into a viscous, clear solution.
The starting materials for
the super amides are the
methyl esters of fatty acids prepared by the displacement of the
glycerol in a
fat by a methyl alchohol. The process described by Bradshaw in Soap,
18,
5,23-24, 69-70, is remarkable not only for producing methyl or ethyl
esters
directly from the fat without intervening hydrolysis, but also for
taking place
at low temperatures, and requiring no alloy steel or other special
corrosion-resistant equipment.
The reaction is carried out
in any convenient open
tank, which may be constructed from ordinary carbon steel. The fat must
be
clean, dry and substantially neutral. It is heated to about 80°C and to
it is
added commercial anhydrous methyl alcohol (99.7%) containing 0.1-0.5%
sbdium or
potassium hydroxide. The quantity of alcohol recommended is about 1.6
times the
theoretical requirements of the reaction, although amounts as low as
1.2 times
theoretical may also be used. Alcohol amounting to more than 1.75 time
the
theoretical quantity does not materially accelerate the reaction, and
interferes
with subsequent gravity separation of the glycerol.
After addition of the
alcohol, the mixture is
stirred for a few minutes and is then allowed to stand. Increased
percentages
of NaOH or KOH speed up the reaction and increase the conversion. The
glycerol
begins to separate almost immediately; since it is virtually anhydrous
and much
heavier than the other liquids, it readily settles to form a layer at
the
bottom of the tank. Conversion of the oil to methyl esters is usually
98 per
cent complete at the end of an hour.
The lower layer of glycerol
contains not less than
90 per cent of glycerol originally present in the fat; the upper layer
consists
of the methyl esters, most of the unreacted alcohol and alkali, the
remainder
of the glycerol, and a small amount of soap. The impurities are removed
from
the esters by successive washes with small amount of warm water.
The methyl esters may be
fractionated to give rather
pure methyl esters of specific fatty acids. To produce the super
amides, with 1
mol of methylesters-l.l mole of diethanolamine is used along with 0.25
per cent
be weight of the total charge sodium methylate as the catalyst. The
reaction is
best carried out at 105ºC for 3-3½ hrs. Methyl alcohol is liberated
during the
reaction, and may be reused for ester interchange. The progress of the
reaction
may best be controlled by collecting and measuring the liberated methyl
alcohol.
The monoethanolamides and
monoisopropanolamides are
wax like substances, practically insoluble in water, but solubilized by
another
hydrophilic anionic or non-ionic detergent and are very easy to
manufacture.
The production process consists in simply heating stoichiometric
amounts of
fatty acids with monoalkylolamine at about 160°C for 2-3 hrs. A very
slight
surplus of monoethanol amine increases the speed of reaction, and can
be
distilled all at the end of the reaction either under atmospheric
pressure or
under reduced pressure.
Table 1, gives the settling
point and man uses of
various monoethanolamides and monoisopropanolamides. The
isopropanolamides show
a lower setting point than the ethanolamides of the same fatty acids.
These
products are usually marketed in the form of flakes produced by running
the
molten products over drilling rolls fitted with doctor blades for
scraping off
the flakes.
Table 1: Setting Points and
Applications and Uses of
Alkylolamides
N-Acyl-N-Alkyltaurates
Introduction
N-acyl-N-alkyltaurates have a
general formula,
RR’NCH2 CH2SO3Na, where R may be oleoyl, cocoacyl, tall oil or tallow
group and
R’ may be a methyl or cyclohexyl group. However, the most commonly used
and
produced product in this group of compounds is sodium
N-Oleoyl-N-methyltaurate.
It is sold throughout the world under various trade names, most common
among
them being IGEPON T.
Igepon T was first introduced
in 1931, by I.G.
Farben industries in Germany and is still in the market in its original
form.
It is sufficiently stable for most textile processing work except the
carbonizing of wool where a strong sulfuric acid bath is encountered.
Igepon T
has enjoyed a steady expansion of market upto the present time in
U.S.A. and
Germany and most other developed countries inspite of the advent of
alkylbenzene sulfonates. In India, however, most of its requirements
are met
through imports.
R1 represents hydrocarbon
radicals of the fatty acid
series which for economic reasons may contain twelve to eighteen carbon
atoms.
R2 represents an alkyl or cycloaliphatic group which should range from
one to
eight carbon atoms. Total carbons in Rl and R2 preferably should not be
less
than twelve nor more than twenty one. Beyond these limits the quality
of the
product falls off sharply in one of several properties. R3 may be a
metal or an
organic base or hydrogen. A computation of the number of possible
products
under the above stated limits might reach 1000.
The effect of changes in
structure are fairly well
defined. Little detergency is obtained unless R1 and R2 combined
contain at
least twelve carbon atoms. Detergency is increased by increasing the
length of
either R1 or R2 or both. The limit is reached at approximately sixteen
carbon
atoms for R1 if the chain is straight and saturated. If unsaturated,
then
maximum detergency occurs at approximately eighteen carbons and it is
believed
that with more unsaturation the maximum length of carbons is further
increased.
Departures from straight chain in R1 by branching or by introduction of
a
solubilizing group, will decrease detergency but increase the wetting
power. A
decrease in the length of R1 increases both solubility and wetting
power. If R1
is kept within twelve to sixteen carbon atoms and if the size of the R2
group
is increased from a methyl to a higher homolog such as the butyl or
amyl group,
the resulting Igepon becomes more soluble inspite of the molecular
weight
increase. If R1 is twelve carbons, the solubility of the Igepon passes
through
a maximum when R2 is a four carbon straight chain. Wetting increases
with
increase in the lengths of R2 until R1 and R2 combined contain
approximately
eighteen carbons. Further increase in R2 brings on a decrease in
wetting. R2
may be hydrogen, but when a taurine is used a substitution of at least
one
carbon group enhances the properties of the resulting product
tremendously. The
choice of a metal for R3 may affect foaming and the power to emulsify
and
disperse other substances. There is little difference in solubility
between the
sodium and potassium salts in the Igepon compounds investigated. The
calcium
salts are much less soluble. The representative types of Igepon T,
currently
manufactured in developed countries such as U.S.A. and Germany are
given in
Table 2.
Although one primary factor
in determining which
Igepon type compounds will be commercially important is the cost of raw
materials, the economic limitations still permit a relatively wide area
of
investigation. The product derived from oleic acid and N-methyl taurine
provides the optimum combination of desirable properties. This compound
is
further recommended by the relatively low price of its raw materials.
Applications of Igepon T Products
Igepon T finds its greatest
use today in the textile
field where it was first introduced. It finds its way into almost every
phase
of textile wet processing. The list of uses include scouring, wetting
out,
degumming kier boiling, dye leveling, dye pasting, chlorine and
peroxide
bleaching, fulling, lime soap dispersing and finishing. It also finds
application in agriculture, paper, leather and metal cleaning; and also
to a
small extent in household products, including dentrifices, shampoos,
cosmetics,
and pharmaceutical preparations. It is also used in the scouring of
feathers,
in electrolytic plating baths, in the washing of automobiles,
airplanes,
railroad coaches and locomotives, rugs, floors, buildings and for
cleaning streets
and roads, and in the dairy, food and for industries.
Table 2: Representative Igepon T’s
Manufactured in U.S.A.
and Germany
Igepon T can be prepared in a
variety of forms. One
is a clear liquid suitable for incorporation into consumer products. It
looks
much like a conventional liquid soap and is available with 15 and 25
per cent
active ingredients. Another form, is a ‘slurry’ or an opaque heavy
liquid. This
material contains 28 per cent active ingredients and is essentially the
product
as it comes from the condensation kettles; it contains no added
chemicals. It
may be used by formulators who-will process it further by adding it to
other
ingredients or drying it to a powder. It can be shipped in tank cars
and is the
least expensive of the various Igepons.
Future of Igepons
The future of Igepon T, its
analogs and homologs, is
bright. The economic existence of this type of product is assured by
the fact
that the biggest weight in its molecule is a fatty acid. The principal
fatty
acid used is oleic acid, which is found abundantly in vegetable and
animal
oils. As synthetic detergents derived from non-fatty soures encroach on
the
soap market, the fats and particularly tallow from which oleic acid is
largely
derived will tend to become more a surplus product.
Another advantage enjoyed by
the taurine type Igepon
(N-acyl-N-alkyltaurates) is the fact that the Igepon T gel, largest
seller in
the group today, is not the best wetter in the series, nor is it the
best
emulsifier or dispersant. It is not the best foamer, the best
textile-softening
agent, or lime-soap dispersant, nor is it the most soluble member of
the group.
It has a good high average on all counts, which led its developers to
call it
the ‘universal soap’. The taurine type Igepon can be modified to well
over 100
varieties. Anyone of the various surfactant properties may be obtained
to a
high degree by making changes in the structure of the Igepon molecule.
Consequently, it is predicted that the Igepon-type surfactants will
have an
important future in the development of special purpose products where
price is
not the primary consideration.
Manufacture
of Igepon T
Raw Materials
The major materials required for the
production of
sodium-Noleoyl-N-methyltaurine are oleic acid, phosphorous trichloride,
N-methyltaurine and caustic soda. It is extremely important that a high
quality
of oleic acid be used in the process. If an excessive amount of esters
or
unsaponifiable material is present, the resultant Igepon will have an
excess of
free fat which tends to make the gels cloudy.
The N-methyltaurine may be
used as a 25 to 30 per
cent filtered aqueous solution. The 30 and 50 per cent caustic soda
solutions
and the hydrochloric acid used to control the pH of the batch at
various points
in the processes can be the standard commercial products.
Oleic Acid Chloride
The first step in
manufacturing Igepon T gel or
Igepon T powder is the production of oleic acid chloride
(oleoylchloride) from
oleic acid and phosphorous trichloride. Acid chlorides other than oleic
may be
used to make special Igepon compounds.
The reaction takes place in a
jacketted lead-lined
kettle equipped with both cooling water and low pressure steam
connections. A
horse shoe type agitator stirrs the charge. A 1.5" lead vent to the
roof
of the building removes volatile acid fumes and decomposition products
of
phosphorous trichloride from the kettle. It is essential that the
kettle be dry
before charging is begun to prevent hydrolysis of the phosphorous
trichloride.
If any condensation accumulates on the kettle due to extended
inactivity, it is
driven off by introducing steam into the jacket while the kettle is
empty.
To begin the operation, oleic
acid is blown by air
from a feed tank to a steel weigh tank; phosphorous trichloride is
similarly
blown into a lead-lined weigh tank. A 400 kg. charge of acid is drawn
from the
weigh tank and dropped by gravity into the kettle. Phosphorous
trichloride (103
kg.) at room temperature is introduced from the weigh tank over a
period of one
hour while cooling water is circulated through the jacket of the
kettle. A
sight glass in the lead line through which the phosphorous trichloride
is
charged permits the operator to judge the flow rate of this stream.
After the
kettle has been completely charged the temperature is raised to 50°C to
52°C
and is held there for 6 hours by introducing 15 kg. steam into the
jacket. At
the end of this period the temperature is raised to 60°C for an
additional 15
minutes to ensure completion of reaction.
The finished product is blown
by air pressure into
two lead-lined cone shaped tanks and allowed to stand overnight to
settle out
the by-product phosphorous acid. The bases of the cones are heated with
extended 1.5" lead steam coils to thin down the heavy acid sludge and
aid
in the separation. After drawing off the first waste acid the contents
of the
cone tanks are agitated and then a second separation of acid is drawn
off. The
point of separation is determined by observation through sight classes
in the
draw-off lines. The spent acid is piped direct to the sewer through
lead pipes
traced with 1.5" outside diameter pipes carrying low pressure steam.
Oleic acid achloride will
descompose on standing if
exposed to atmospheric moisture consequently it is made up only as
needed and
is piped through steam traced lead lines direct from the cone tanks to
the
weigh tanks of the Igepon unit.
This product is made in a
brick-lined kettle
equipped with a four fingered stainless steel agitator. A stainless
steel
submerged coil provides temperature control. The kettle has stainless
steel
feed lines for oleic acid chloride and hydrochloric acid and caustic
solution.
a stainless steel thermometer well, and a lead vent pipe. Air for
forcing the
charge out of the kettle is introduced into the vent pipe.
A stainless steel kettle,
equipped with an
anchor-type agitator is also available. Process temperatures in this
kettle are
controlled by a steel jacket connected to both steam and cooling water
lines.
Inlets and vents are arranged similarly to those in the larger kettle.
To begin the batch 25 to 30
per cent aqueous
solution of N-methyl-taurine is blown over from the storage tanks until
an
amount of solution equal to 89.25 kg. of N-methyltaurine has entered
the weigh
tank. The correct gross weight of this charge, based on the
N-methyltaurine
analysis of the storage tank, is supplied to the operator by the
analytical
laboratory. This charge is then dropped by gravity into the reaction
kettle and
the flow of cooling water is started in the jacket to bring the
temperature of
the charge down to 22° to 25°C. Water weighed in the same weigh tank is
then
added to bring the total weight of the charge at that point to 1296 kg.
Addition of 30 per cent aqueous caustic solution is begun and when the
equivalent of 14.25 kg. of sodium hydroxide has been weighed in, oleic
acid
chloride is introduced from a lead-lined weigh tank.
The caustic and acid chloride
enter the kettle
through separate perforated stainless steel pipes below the level of
the
initial taurine charge. This practice minimizes the liberation of
noxious
fumes, reduces the corrosive effect of the acid chloride above the
liquid
level, and safeguards against side reaction between sodium hydroxide
and oleic
acid chloride.
Simultaneous addition of the
two reactants is
continued for 4 to 6 hours until a total of 43.5 kg. of sodium
hydroxide and
214.2 kg. of about 92 per cent oleic acid and chloride have been
charged. The
rate of addition of these two solutions is adjusted to maintain a
slight
stoichiometeric excess of sodium hydroxide in the kettle at all time as
determined by spot tests on triazine paper
2-(4-nitro-O-tolyldiazoamino-4-sulfobenzoic acid).
After all the reagents have
been added, the charge
is agitated for an additional hour to ensure completion of reaction.
Cooling water
is circulated through the coils at maximum flow rate during the entire
reaction
period. During the winter months the temperature of the charge is about
22°C at
the beginning of the reaction and rises to 27°C. However, in the summer
time
the final temperature may go as high as 40°C.
After the reaction has been
completed a sample is
taken and the percentage of excess N-methyltaurine is determined by
coupling
with diazotized m-nitraniline. It is desirable to have a slight excess
of
N-methyltaurine in the product to ensure that the reaction has gone to
completion. After completion of the reaction hydrochloric acid is added
to the
kettle through a glass and rubber siphon from a carbon mounted on a
platform
scale. Acid is added until the charge gives a slightly red spot test
with
brilliant-yellow paper (pH 6 to 8). This neutralization usually
requires about
15.3 kg. of acid. In making some of the special Igepon products
additional
hydrochloric acid may be needed at this point.
In making the standard T gel
the neutralized batch
is diluted to 1734 kg. with water and 0.725 kg. of a light floral,
liquid
perfume. The charge is then heated to 55°C and held there for 1.5-
hours. The
charge is blown into white oak, gum or ash wood barrels. Air used to
blowout
the batch passes through a trap to remove rust particles which would
tend to
darken the finished product. As a further precaution against
contamination, a
0.007" opening stainless steel filter on the product discharge line
removes all solid particles from the liquid product before it enters
the
shipping containers. The barrels are allowed to cool on the shipping
platform,
and when the Igepon reaches a temperature of about 40ºC it sets up as a
firm,
opalescent gel.
Igepon T gel may be shipped
in polyethylene lined,
fibre board drums or wooden barrels. The batch yields about 1090 kgs.
gel.
having a composition of 15.3 to 16.3 per cent
Sodium-N-oleoyl-N-methyltaurine;
0.8 to 1.0 per cent sodium oleate; 0.14 per cent N-methyltaurine, 4.0
per cent
sodium chloride and 78 per cent water. This represents approximately
the
theoretical yield.
Igepon T Powder
In manfacturing this product
the initial charge of
30 per cent N methyltaurine solution contains 95 kg. of 100 per cent
N-methyltaurine, and when diluted with water to 1224 kg it gives a
slightly
more concentrated solution than that used in the gel process. As a 30
per cent
solution 17.6 kg. of sodium hydroxide are added to this intial charge
to keep
the reaction mixture on the alkaline side. Then 226.5 kg. of technical
oleic
acid chloride are added simultaneously with 30 kgs. of sodium hydroxide
as a 30
per cent solution over a period of 4 to 6 hours, as in gel production.
The batch is stirred for 1
hour after charging is
completed and any excess of N-methyltaurine is reacted with additional
acid
chloride and caustic soda as in the production of gel. The completely
reacted
charge is then heated to 50°C by the steam coils and neutralized to the
brilliant-yellow and point with hydrochloride acid. Immediately after
neutralization 530 kgs. of common salt are dumped into the batch from
bags, and
water is added to bring the total weight of the batch to about 2652
kgs. At
this concentration, about 36 percent solids, the salt is completely
dissolved.
It is important that no suspended solid material remains in the charge
because
it would plug up the nozzles of the spray drier. If the pH of the batch
after
the addition of the salt does not fall between 7.1 and 7.3, sodium
hydroxide or
hydrochloric acid is added to adjust the pH within these limits.
The salt-loaded mixture is
blown from the reaction
kettles into a 3/8" lead-lined sted feed tank. The charge is heated to
50°C by lead steam coils in the feed tank, and then is pumped to the
three
10-gallon feed pots of the spray dryer. The dryer atomizers use air at
80
Ibs/in2, pressure heated to maintain 50 Ibs. pressure at the injection
nozzles
to ensure adequate atomization in the tower. Air supplied to top of the
dryer
is preheated to about 225°C, by an oilfired furnace and forced into the
dryer
by a centrifugal fan at a rate of about 250 cubic feet per minute. The
major
part of the dried powder is discharged from the bottom of the dryer
tower and
carried along by the added cold air into the primary cyclone separator
from
which it drops directly into a transfer drum. About 10 per cent of the
product,
however, is carried through the cyclone and is re-introduced into the
dryer
chamber. A second take-off from the dryer chamber is located just above
the
bottom taper. This duct carries a more dilute stream of air-borne
powder into a
larger, secondary cyclone separator. The solids, which fall out in this
separator, are refluidized by more cold air and returned to the top of
the
primary cyclone. The overhead from the secondary cyclone, containing 7
to 10
percent of the product is introduced into a water scrubber. One water
spray
above the inlet and three below remove all but about 2 per cent of the
product
from the dryer exhaust. The scrubbed air is vented to the atmosphere.
The
liquor is drawn from the bottom of the tower into a storage tank. Make
up water
is added to this tank by an automatic level control. A high silicon
iron pump,
drawing from the tank, recycles water to the spray nozzles and supplies
process
water to the condensation kettle.
If a kettle batch is made
each day the dryer feed
pots can be kept full and provide an uninterrupted feed to the dryer.
Under
these circumstances the dryer can handle as much as 180 to 200 kg.
Igepon per
hour, as it has a rated capacity of 335 kg. water per hour. The product
comes
from the dryer as low density granules which are lightly milled in a
paddle
mixer to break up the larger lumps and to mix in 500 grams of a light
floral
perfume per ton of Igepon. From, the mill the powder is dropped
directly into
the open top steel drums in which it will be shipped. Yields of
powdered
product run about 836.4 kg. per batch and analyze about 30.5 to 32.5
per cent
oleoyl-methyltaurine, 1.5 to 3.0 per cent sodium oleate, and 0.14 to
0.8 per
cent N-methyltaurine; the remainder of the powder comprises inorganic
salts.
Chief among these is sodium chloride and a trace of sodium sulfate.
However,
phosphite salts (about 3 per cent) are also present; these are formed
from the
excess phosphorous trichloride dissolved in the oleic acid chloride.
The yield
is about 91 per cent of theory.
Chemical Control
Chemical control on the
Igepon T operation is
relatively simple. By experience, rule of thumb knowledge can be
accumulated,
which tells the operators whether the reaction is going properly. At
some
points analytical samples are taken merely as a precaution and only
analyzed if
trouble develops later in the operation.
The phosphorous trichloride,
oleic acid and
N-methyltaurine are checked for rigid spacifications each time a
shipment of materials
arrive at the factory. The acid chloride charged to the reaction kettle
is
analyzed the oleic acid chloride, phosphorous trichloride, and free
fatty acid.
After the condensation is complete the batch is checked for pH and
residual
N-methyltaurine. The pH is checked by a standard calomel cell pH meter
and is
then adjusted as explained in the operation procedure.
After the pH has been
adjusted it is checked again,
and the final shipping sample is sent to the laboratory. This final
sample is
examined for clarity, viscosity, and alkalinity. A 10 per cent water
solution
of this sample must be perfectly clean and must have a pH between 7.2
and 7.5
at this point.
The Igepon T powder undergoes
an almost identical
analysis routine. If the content of oleoylmethyltaurine falls outside
of the
permissible limits, it is blended into the subsequent batches at the
ribbon
blender.
Utilities
In the Igepon process steam
is used only for process
heating. Since the temperatures required are all reasonably low, steam
at 100
psi is adequate for this operation. Compressed air is used in the plant
for
forcing liquids from one vessel to another, the 45 psi air is
sufficient. The
air used for transfering phosphorous tricoloride is passed through a
dryer and
filter to present hydrolysis and contamination. The purifying unit
consists of
a liquid trap, a steel chamber 12†in diameter and 6' long filled with
quick
lime to dry the steam, and a similar tank 4' long containing a cloth
bag filler
to remove any particles of lime or other solids that might be carried
over into
the phosphorous trichloride tanks.
The spray-drier may have a
separate compressor which
provides 90 lb/in2 air for atomization.
Materials of Construction
The corrosion problem is not
critical in the
operations as described, but some special materials must be used.
Carbon steel
is suitable for most vessels. However, those which must contain
phosphorous
trichloride or oleic acid chloride are homogeneously lead bonded. This
type of
lining is applied by tinning the entire inner surface of the steel
vessel and
then soldering the lead lining plates to the whole steel surface. This
technique eliminates the problem of buckling and blistering. It also
means that
in the event of failure of the lining only the steel directly behind
the gap in
the lining is attacked. In the so called ‘loose lining’ technique in
which the
lead sheets are tacked to the shell, only along with seams, a failure
at any
point usually means that the corrosive contents of the vessel will
shortly
enter the entire space between the lining and the vessel wall. The
spray drier
feed tank may be lined in this fashion, but only moderate temperature
are
encountered in this tank and the agitation is never violent.
In general, the lead linings
in the Igepon process equipment
last 7 to 9 years before they must be replaced. The reaction kettles
may be of
stainless steel. If however, it is brick lined construction it may
require
re-lining after about each two years. All equipment which comes in
contact with
finished liquid Igepon is made of stainless steel, since the detergent
will
exchange cations with ordinary steel to form iron salt which has an
undesirable
dark colour.
Submerged steam lines in the
brick lined kettle are
stainless steel; in the spray dryer feed tank these are lead. The other
kettles
are equipped with external jackets. Agitators are either lead-covered,
stainless steel, or in the case of the spray drier feed tank, wooden.
Neither stainless steel nor
lead will stand up in
the duct which carries the moist exhaust from the spray drier. Nickel
or high
nickel alloy serves well. The spray drier itself is made of carbon
steel.
Tanks which must withstand
static pressure such as
those employing air pressure transfer are entered and inspected, and
subjected
to hydraulic testing every 2 years. Unpressurized steel tanks which
store
corrosive liquids are on a similar inspection schedule. Storage tanks
in
non-corrosive service are inspected every 5 years. Kettles are also
inspected
at 5 years intervals. Jacketted kettles are lifted out of their
jackets, and
the surfaces are cleaned and inspected for pits. Pits usually occur in
the
welded seams. If the welds are badly pitted below the surface of the
adjacent
plates the bead is chipped off and the seam rewelded.
Since most of the materials
involved in the process
are transferred through the plant by air pressure, pumps present only a
limited
corrosion problem. Where pumps are used they are of motor driven
centrifugal
type. Where pure oleic acid must be pumped, a high alloy steel pump is
used.
All other pumps are of carbon steel.
Stainless steel valves are
used on all lines which
transfer finished liquid Igepon T. Pipe lines which carry liquid Igepon
T also
are of stainless steel. Those which transfer oleic acid chloride are
lead lined
and steam-traced. The steam-tracing is only used in the winter when the
acid
chloride has a tendency to thicken and move sluggishly.
Bleaching Agents
A bleaching agent may be
defined as a compound,
which is used to remove color from natural or artificial products and
thus
whiten them.
History
From earliest times until the
end of the 18th
century, the only known method of bleaching cloth was a process which
required
steeping the fabric in solutions of alkali derived from limestone, wood
ashes,
or kelp, followed by treatment with lactic acid from sour milk, and
after
rinsing, repeated exposure of the moist cloth to sunlight. Natural
fibers
contain certain oils, waxes, dirt, etc which can be completely or
partially
removed by the aqueous alkali. The action of sunlight, particularly
ultraviolet
radiation, activates the oxidation of the remaining colored substances
to a
colorless form or renders them soluble.
Bleaching of cloth by this
method was not widely
used until after the Renaissance when there was a demand from the
masses for
bleached cloth. Most of the material bleached was linen, since cotton
was
considered to be sufficiently white without bleaching and hemp, jute,
and other
fibers were too difficult to treat.
In the 18th century, the art
of bleaching reached
its greatest perfection near Haarlem, Holland. Linens woven in Britain
and
elsewhere were sent to Holland in the spring for bleaching and returned
to the
weavers in the fall for finishing and marketing. The method was
established in
Ireland by the middle of the century and improved by the use of dilute
sulfuric
acid instead of sour milk.
The obvious disadvantages of
the method were the
length of time required and the fact that the land used in this way was
not
available for essential farming.
In 1774, Carl Wilhelm Scheele
discovered elemental
chlorine and observed its bleaching effect on vegetable fibers.
However,
aqueous solutions of chlorine caused too much tendering of the cloth.
The
French chemist Berthollet found that chlorine could be absorbed in
solutions of
caustic potash or carbonate to give a satisfactory bleaching agent.
Commercial
production of these solutions was undertaken in Javelle, France and the
potassium hydroxide product, called “eau de Javelle,†was first applied
to
cloth in about 1786. Labarraque substituted caustic soda or soda ash
for
caustic potash, calling his product “eau de Labarraque.†Subsequent
development
of the LeBlanc process for soda ash made “eau de Labarraque†less
expensive and
it soon replaced “eau de Javelleâ€.
In 1799 Charles Tennant, in
Scotland, prepared
bleaching powder from chlorine and slaked lime. The discovery of
bleaching
powder made possible for the first time a product which could be
shipped in
solid form from a chemical plant to a textile mill, thus eliminating
the need
for chlorine-generating plants at each mill. Chemical bleaching then
completely
replaced the old bleach fields of England, Ireland, and Holland.
Bleaching powder remained the
most important textile
bleach until after World War I when tank cars were developed to ship
liquid
chlorine. It then became more economical to ship liquid chlorine and
caustic to
the mills to form liquid bleach at the point of use. However, tropical
bleach,
which is a more stable material produced by the addition of quick lime
to
bleaching powder, is still used in significant amounts in the
underdeveloped
areas of the world.
Hydrogen peroxide was
prepared by Thenard in 1818 by
reacting dilute sulfuric acid with barium peroxide. Peroxide had little
or no
use as a textile bleach during the 19th century. Electrolytic
production of
hydrogen peroxide, which began in 1908, reduced its cost. By the end of
the
1920s, when strong solutions of about 30% hydrogen peroxide were
available,
peroxide was used extensively to bleach cotton goods. The adaptability
of
hydrogen peroxide to continuous bleaching operations started a
mechanization
trend in the industry. Hydrogen peroxide has now largely replaced
sodium
hypochlorite in the textile industry.
It is interesting to follow
the parallel development
of the bleaching of wood pulp. The ancient bleaching process was too
lengthy
and expensive for use on paper stock and the whiteness of paper
depended upon
the use of sorted white rags. While there is some disagreement as to
the date of
the first use of chlorine for bleaching rags and pulp, evidence exists
that
chlorine was being manufactured and used for this purpose by the Gilpin
Paper
Mills in Delaware by the summer of 1804.
In 1854, Watt and Burgess
obtained U.S. Patent
11,343 for caustic pulping. Although the three-stage process involving
chlorination followed by alkaline extraction and hypochlorite bleaching
was
well known by 1875, the fact that liquid chlorine could not be
transported or
easily handled prevented any extensive use. Therefore, pulp was
bleached mainly
in a single-stage process using bleaching powder. After tank cars for
transporting liquid chlorine were developed during World War I, the
three-stage
process began to be used for sulfite pulp, and with additional stages,
was
adaptable to bleaching Kraft pulp. Batch chlorinators eventually gave
way to
continuous chlorination. Nakoosa-Edwards Paper Company first reported
large-scale chlorination of pulp in 1930 and 1932.
In an effort to obtain
increased brightness with minimum
degradation of pulp, other oxidizing agents were introduced. The
development of
sodium chlorite as a commercial bleach in the 1930s provided a chemical
which
could be used for a final brightening with little damage to the
cellulose. The
active agent in the process is chlorine dioxide, which can now be
obtained more
economically by using generators containing sodium chlorate, sulfuric
acid, and
a reducing agent such as sulfur dioxide, hydrochloric acid, or
methanol. Other
chemicals used experimentally for final brightening are sodium
peroxide,
perborates, percarbonates, peracetates, and ozone. The cost of these is
often
prohibitive.
Sodium chlorite is also an
effective bleach for
textiles and is used for both cotton and synthetic fibers. In addition
to bleaching
pulp, chlorine dioxide is used for the bleaching of flour and sugar and
for
upgrading inedible fats and oils.
Another important use of
bleaches is in commercial
and home laundries. Initially, bleaching powder was used. Sodium
hypochlorite
solutions and calcium hypochlorite have since replaced bleaching
powder. The
most recent products introduced for laundry use are mixtures containing
chlorinated hydantoins and chlorinated isocyanuric acids. The latter
are also
active ingredients in cleanser formulations.
Certain reducing agents are
used as bleaches. Sulfur
dioxide had been used as a bleach since Roman times. It has several
considerable disadvantages when applied to vegetable fibers, but can be
employed to bleach wool with little damaging effect. Sulfur dioxide as
well as
thiourea and sodium dithionate are excellent antichlors to remove
traces of
chlorine or other oxidizing bleaches.
Mechanism of Bleaching
A successful bleaching
process must remove colored
impurities by converting them to colorless compounds and/or to
compounds which
are soluble.
In many cases, color in a
molecule is attributed to
the presence of conjugated double bonds, that is, a series of alternate
single
and double bonds, with atoms or groups at the end of the chain which
can exist
in two states of covalency, thus permitting resonance and resulting in
color.
Bleaching can be achieved by any agent which will disrupt the
resonating
structure, either by reaction with one of the conjugated double bonds
or by
oxidation or reduction of the group at the end of the chain.
Chlorine often bleaches by
adding across double
bonds or by oxidation, but at the same time causes undesirable
tendering of
fabric. Acidic chlorination is used as the first-stage bleach in the
preparation of wood pulp because of the high concentration of reactive
impurities. At low pH values, te equilibrium below is shifted to the
left and
Cl2 + H2O = HOCl + H+ + Cl–
chlorination of lignin is achieved
together with some
oxidation but without severe degradation of the cellulose since the
concentration of hypochlorous acid is low.
Bleaching
agents which furnish
hypochlorous acid in solution will chlorohydrinate a double bond,
adding an OH
group on one side of the bond and a Cl on the other. The latter is
usually
hydrolyzed and replaced by an OH group fairly rapidly to form a
1,2-glycol.
Peroxides form epoxides across double bonds. Under bleaching
conditions, the
epoxide is converted to a 1,2-glycol. In both cases the 1,2-glycol may
be
oxidized, breaking the single bond between the carbons to form two
carboxylic
groups.
Chlorine dioxide will not
attack an isolated double
bond. Although its bleaching ability depends upon an oxidation process
and its
use involves little or no damage to the fiber, the mechanism of its
action has
not been established.
Reducing agents can sometimes
hydrogenate a double
bond.
Hypochlorous acid and
hypochlorites bleach colored
organic compounds which contain no conjugated double bonds by
chlorination to
form a colorless product or by oxidation in which extensive breakdown
of the
molecule frequently occurs.
Generally,
bleaching reactions are
not reversible.
Bleaching is a complex
process which cannot be fully
explained or predicted. The succession of treatments used and the
conditions
employed in each step are determined empirically to produce the most
favourable
result.
Bleaching Strength
The strength of a bleaching
agent is expressed in
terms of “available chlorine†in the case of chlorine-containing
bleaches and
“active oxygen†in the case of oxygen containing bleaches.
Available Chlorine. Available
chlorine is defined as
the measure of the oxidizing power of the chlorine present in the
compound. It
is expressed in terms of chlorine with a gram equivalent weight (geq
wt) of
35.45.
In an oxidation process, the
reactions of chlorine
can be considered as follows:
It can be seen that in the
case of hypochlorites,
the chlorine present in the molecule has twice the oxidizing power of
elemental
chlorine; in chlorine dioxide the chlorine has five times the oxidizing
power
of elemental chlorine and in sodium chlorite the chlorine has four
times the
oxidizing power. Therefore, when the oxidizing power is calculated as
chlorine
in available chlorine determinations, the result will be greater than
the
actual% chlorine in the bleaching agent. For example, sodium
hypochlorite
contains 47.62% chlorine and 95.24% available chlorine. Chlorine
dioxide
contains 52.56% chlorine and 262.8% available chlorine.
The available chlorine
contents of various
chlorine-containing bleaching agents are given in Table 1.
Other oxidizing agents may be
analyzed by the
available chlorine procedure and their oxidizing power expressed for
purposes
of comparison as% available chlorine. For example, hydrogen peroxide
has the
equivalent of 208% available chlorine.
Active Oxygen. Active oxygen
is the measure of the
oxidizing power of compounds, such as inorganic perborates,
percarbonates, or
peroxides, which release hydrogen peroxide in acid solutions. It is
expressed
in terms of oxygen (O) with a geq wt of 8.00.
The
active oxygen contents of
oxygen-containing bleaches are given in Table 2.
Table
2: Active Oxygen Contents
of Oxygen-Containing Bleaches
Methods of Analysis
Bleaching formulations
generally contain only one
active bleaching agent. The analyst is therefore not concerned with a
separation of bleaches but rather with the identification and assay of
the
single bleaching agent present.
Identification
An unknown bleach sample
should first be analyzed
for total chloride by the Mohr method. A second analysis should be done
in
which 8% hydrogen peroxide is added until the evolution of oxygen
ceases,
followed by the standard chloride determination. If the total chloride
found in
the second determination is greater than that in the first, a
chlorine-containing
bleach is present. If the two chloride determinations are identical, an
oxygen-containing bleach is indicated.
In the case of
chlorine-containing bleaches, a
positive test for calcium indicates calcium hypochlorite. Organic
chlorine-containing bleaches as well as calcium hypochlorite can often
be
identified by infrared spectroscopy using the potassium bromide pellet
technique on the original sample. Dichlorodimethylhydantoin can be
separated
from a formulation, if desired, by virtue of its solubility in
methylene
chloride or chloroform. Trichloroisocyanuric acid is very insoluble in
water
(1.2 g/100 ml at 25ºC) and as a result may be separated from inorganic
builders. Sodium and potassium salts of dichlorocyanuric acid can best
be
identified by infrared and/or emission spectroscopy.
Oxygen-containing bleaches
can be identified by
infrared spectroscopy or elemental analysis. The presence of boron
indicates
perborates; a positive test for sulfur indicates persulfates.
Assay Methods
Chlorine-Containing Bleaches
Chlorine-containing bleaches
are assayed by
iodometric or iodimetric determination of the available chlorine. The
methods
for specific compounds are discussed.
Calcium Hypochlorite, Bleach
Liquor, and Tropical
Bleach. For these compounds, available chlorine is determined
iodometrically by
titration with standardized sodium thiosulfate solution of the iodine
released
by treatment with potassium iodide and acetic acid.
Procedure
Transfer 3.6-4.0 g of sample
to a tared,
glass-stoppered weighing bottle and weigh to the nearest 0.1 mg. Place
a dry
powder funnel in the neck of a 500-ml volumetric flask containing about
100 ml
of water. Carefully transfer the sample through the funnel into the
flask and
rinse the weighing bottle and funnel with a fine stream of water.
Stopper the
flask and swirl the solution until must of the sample has dissolved.
Dilute to
volume with water, stopper, and mix thoroughly. While shaking or
swirling to
keep any solids in suspension and to insure representative sampling,
pipet a
25-ml aliquot into a 500-ml Erlenmeyer flask containing 125-150 ml of
water.
Add 2 g of potassium iodide crystals, mix, and add 8 ml of glacial
acetic acid.
Mix and titrate at once with standardized 0.1 N sodium thiosulfate
solution to
a pale yellow color. Add 2 ml of 0.5% starch indicator solution and
continue
the titration until the blue color just disappears.
Sodium Hypochlorite. A
procedure similar to the one
for calcium hypochlorite is used for the determination of available
chlorine in
sodium hypochlorite solution.
Procedure
Dilute a 10.00-ml sample to
1000 ml in a volumetric
flask. Dissolve 2-3 g of potassium iodide crystals in 50 ml of water in
a
250-ml Erlenmeyer flask. Add 10 ml of acetic acid, then pipet a 100-ml
aliquot
of sample into the solution, keeping the tip of the pipet beneath the
surface
of the solution until drained. Titrate at once with standardized 0.1 N
sodium
thiosulfate until the solution is a pale yellow color. Add 1 ml of 0.5%
starch
indicator solution and continue the titration until the blue color just
disappears.
Dry Cleaning Agents
Drycleaning of garments is
done in much the same
manner as laundering, except, that organic solvents are used in place
of water.
As in laundering, detergents are added to the solvent to enhance its
cleaning
quality. Other solvent additives are used to give the textile the
desired
finish. This may be done merely to improve the “hand†or “drape†of the
textile, or chemical additives may be used to achieve water repellency,
insect
repellency, or flame resistance.
Drycleaning washers are
similar in construction to
commercial laundry washers, but in drycleaning provision is made for
clarifying
the solvent for reuse. In laundering the used wash water is discarded;
this
cannot be done with the more expensive drycleaning solvents.
In the drycleaning system the
solvent is
continuously pumped through the washer and then through some type of
filter
designed to remove all suspended soil. Provision is also made for
distillation
of the solvent to free it from the solvent-soluble soil.
The filters also contain
activated carbon to absorb
dissolved dye which would otherwise build up in the solvent.
Other chemical products used
in small quantities by
drycleaners are formulated to remove stains by local application to the
affected area of the garment.
Only two classes of solvents
have proved suitable
for drycleaning: petroleum fractions and a few halogenated
hydrocarbons. All
other classes of solvents fail to meet the following eight major
requirements
of a drycleaning solvent.
        Â
a.        Â
It must not weaken, dissolve, or
shrink the ordinary textile fibers.
        Â
b.        Â
It must not remove the common dyes
from fibers.
        Â
c.        Â
It must be an acceptable solvent for
fat and oils.
        Â
d.        Â
It must not impart an objectionable
odor to drycleaned textiles.
        Â
e.        Â
It must be sufficiently volatile to
permit reclamation by distillation and to permit garments to be dried
without
prolonged heating at excessive temperatures.
        Â
f.        Â
It must be noncorrosive to metals,
either when dry or in the presence of water.
        Â
g.        Â
It must be relatively nontoxic.
        Â
h.        Â
It must have a flash point of 100° F
or above.
The major drycleaning
solvents used in the U.S. are
the petroleum fraction called Stoddard solvent of which there are four
types perchloroethylene,
and to a
limited extent, trichlorethylene and trichlorotrifluoroethane.
With the exceptions of the
solvents, the chemicals
used in drycleaning are sold as brand-name formulations, and the only
tests
performed on them are the determination of the amount of detergent in
the
solvent, and the amount of water in a solution of detergent in solvent.
However, these chemicals are tested to determine how well they perform
the
function they are designed for according to a number of procedures
developed by
the National Institute of Drycleaning (NID).
Stoddard Solvent
Much of the drycleaning done
in the United States
employs a solvent, corresponding to a petroleum fraction with a minimum
flash
point of 100°C. This solvent has been named Stoddard solvent for W.J.
Stoddard.
The first commercial standard for a drycleaning solvent, CS3-28, was
issued in
1928 by the National Bureau of Standards. The latest, revision of this
specification is CS3-41; it also became an ASTM standard, D 484-52.
Table 1
summarizes the current specifications of regular Stoddard solvent.
Today, three other petroleum
fractions are also
broadly termed as Stoddard solvents. These are the 140°F solvent, the
low end
point solvent, and the odorless solvent.
l40°F
Solvent. This
solvent is safer than the regular Stoddard solvent. Therefore, it may
be used
in locations where Stoddard solvent is prohibited. Also, building codes
for
plants using 140°F solvent are not so rigorous. For example, explosion
proof
motors and other electrical fixtures are not required. Plants using
this solvent
are designated Class 3 in the Handbook of the National Fire Protection
Association.
Low
End Point Solvent.
This type of Stoddard solvent has a dry point in the range of
330-362°F,
compared with 368-409°F for the regular Stoddard solvent. The result is
a rapid
drying solvent. There is no specification covering this solvent. It is
regarded
as a premium grade because of the fast-drying feature.
Odorless
Solvent. Whereas
regular Stoddard solvent is specified to be free of objectionable odor,
this
new class of Stoddard solvent is free of all odor. This is achieved by
removing
or hydrogenating all aromatic compounds. The solvent also meets all
requirements for a nonsmog-producing solvent, since smog production is
related
to the aromatic content.
Odorless solvent is also
regarded as a premium grade
of Stoddard and is not covered by a separate specification.
Specification Tests
Some comments to the
specification tests for
Stoddard solvent are given here.
Odor. The term
sweet as used in the specification
means the opposite of rancid or sour. Although the usual methods of
clarifying
solvent in a drycleaning plant remove odors that accumulate during
continued
drycleaning, these processes do not always remove odors caused by
improper
refining. Therefore, the solvent, when received from the refinery,
should be
free from undesirable odor. There is nothing to show whether or not a
solvent
meets the requirement except the opinion of the examining chemist. Many
samples
of Stoddard solvent have a rather strong odor, but it is easily removed
from
the fabric by conventional drying methods.
Flash
Point. The flash
point is governed by those portions of the solvent that have the lowest
boiling
points and are therefore the most volatile. Since these portions
evaporate more
rapidly than the rest of the solvent, the flash point of Stoddard
solvent in a
drycleaning system gradually rises with use. Soaps, prespotters, or
other added
materials sometimes contain low-flash solvents (such as some alcohols)
that
lower the flash point of the solvent and increase the fire hazard. The
introduction of even small amounts of methyl, ethyl, or isopropyl
alcohol into
a washer lowers the flash point of the solvent below normal room
temperatures.
A lighted match, held over
Stoddard solvent at
ordinary room temperatures, does not ignite the solvent because the
solvent is
not giving off enough vapor to form a combustible mixture with the air.
If the
temperature of the solvent is raised, vapor pressure is increased, and
the air
above the solvent becomes richer in solvent vapors. Finally, a
temperature is
reached where enough solvent has vaporized to form a combustible
mixture with
the air. If a flame is then introduced above the solvent, the vapors
will
flash. The lowest temperature at which this occurs is called the flash
point.
Since the flash point of Stoddard solvent may not be under 100°F, there
is no
danger of fire from solvent vapors until the temperature of the solvent
rises
to 100°F or above.
The flash point specification
is frequently
violated. In some cases, the refinery may have set the lower limit of
the
distillation range too low. Such violations usually result in a solvent
with a
flash point of 98 or 99°F. A more dangerous type of violation, however,
results
from careless handling of the solvent. For example, Stoddard is
sometimes
transported in tank trucks that were previously used for carrying
gasoline and
still contain small qnantities of gasoline. As little as 1% of gasoline
in
Stoddard solvent lowers its flash point, considerably.
The flash point is determined
by ASTM D 56-64
method.
Corrosive Properties.
Improperly refined solvent may
contain traces of dissolved free sulfur, which can corrode the metals
of
storage tanks and equipment. The corrosion test is carried out
according to
ASTM D 1616-60, at, an elevated temperature, 121°F. Under these
conditions,
corrosion that would be apparent after considerable use of the solvent
at room
temperature can be seen after only 3 hr.
Distillation
Range. From
the standpoint of a drycleaning solvent, there are disadvantages in
products
containing very low-or very high-boiling hydrocarbons. Low-boiling
hydrocarbons, petroleum ether and gasoline, cause fires and high
evaporation
loss; high-boiling hydrocarbons, such as kerosene, cause excessive
drying time.
The distillation range for Stoddard solvent is between 300 and 410°F, a
range
not low enough to cause undue fire hazard and evaporation loss, or high
enough
to prolong the drying time.
The distillation range of
Stoddard solvent is
determined according to ASTM D 86-66 and D 1078-67.
Residue.
Excessive
nonvolatile matter in the solvent often contributes to odors and
lengthens
drying time. Because of the high temperatures used, a small amount of
odorous
residue is usually formed during the distillation test. A sample of the
same
solvent evaporated on a steam bath, where temperature is not raised
above
212°F, yields a smaller and less odorous residue. The residue of
Stoddard
solvent is determined according to ASTM D 1078-67.
Acidity.
If the solvent is
given a sulfuric acid treatment in the refinery and not followed by a
neutralizing treatment (such as with caustic soda), it will contain
small
amounts of sulfuric acid or other acidic materials. Even small amounts
of
sulfuric acid are undesirable in a drycleaning solvent, as they corrode
equipment and damage garments. Fortunately, almost without exception,
drycleaning solvents pass the acidity test.
Sulfuric acid has a very high
boiling point,. The
presence of this substance in the solvent will be as residue in the
flask after
the distillation. If a residue of 1 ml remains from distilling 100 ml
of
solvent, any sulfuric acid present is concentrated there 100 times.
Thus, it,
is logical to test the residue from distillation for sulfuric acid.
According to ASTM D 1093-65,
the solvent sample is
shaken with water and one drop of a 0.1 % methyl orange indicator
solution is
added to the aqueous layer; there should be no change in the color of
the
indicator.
Doctor
Test. Mercaptans
impart to the solvent unpleasant odors, which may be absorbed onto the
garments
during drycleaning. The doctor test is a qualitative method to
determine
whether the treatment for mercaptans was properly done in the refinery.
Sulfur
and sodium plumbite are added to the solvent in a test tube. If
mercaptans are
present in the solvent, the reaction proceeds and the black lead
sulfide formed
is indicative of a positive test.
2
RSH + S + Na2PbO2 ® R2S2 + PbS +
2 NaOH
Sulfuric
Acid Absorption Test.
This test determines if the solvent contains appreciable amounts of
unsaturated
hydrocarbons. These would be in the solvent if it was inadequately
treated with
sulfuric acid during refining. Since unsaturated hydrocarbons turn
rancid and
cause undesirable odors in drycleaned garments, it is imperative that
they be
removed before the solvent leaves the refinery.
In
the test concentrated sulfuric
acid is added in a graduated cylinder to the solvent and shaken.
Sulfuric acid
reacts with any unsaturated hydrocarbons present, and most of the
products of
the reaction settle into the acid layer; thus the volume of the solvent
is
decreased. Since some of the products formed from the reaction remain
in the
solvent layer, the test does not give a quantitative measure of
unsaturated
hydrocarbons; that is, a 5% absorption of the solvent by sulfuric acid
actually
represents a greater percentage of unsaturated hydrocarbons in the
solvent.
Variations in the strength of
commercially available
concentrated sulfuric acid, cause variations in the sulfuric acid
absorption
test. Therefore, the acid strength must be standardized if
reproducibility is
desired.
Perchloroethylene
Perchloroethylene
(tetrachloroethylene) became an
important drycleaning solvent because of its nonflammability, which
permits its
use in places where all types of flammable solvent are either forbidden
by
codes or inhibited by high insurance rates. Its general properties are
given in
Table 3, and the specifications proposed by the NID are listed in Table
4.
Table 3: Properties of
Perchlorethylene
Specification Tests
The following specification
tests were developed by
the NID.
Residual Odor.
Any residual odor left in a fabric
after treatment in the solvent is objectionable. Detection of such
odors by
smelling is more sensitive if the fabric is steamed immediately prior
to the
test. A swatch of bleached but unfinished cotton poplin, Style A-400W,
Testfabrics, Inc., is used and subjected to the following test.
Procedure
Condition the cotton at 60%
relative humidity for at least
8 hr prior to use. Soak
the swatch in
perchloroethylene for 5 min, then remove it and hang it to drain dry
for about
4 hr. Tumble the swatch in a tumble dryer for 30 min at 140°F.
To test for odor, grasp the
swatch in the center
with a forceps, hold it in live steam for 5 sec, and smell it
immediately. Test
an untreated swatch simultaneously. There should be no discernible
difference
in odor between the two swatches.
Nonvolatile
Residue. This
test detects the presence of nonvolatile impurities in the solvent. It
is
determined gravimetrically by evaporating a measured quantity of
solvent and
weighing the residue as follows.
Procedure
Dry a 4 in. diameter evaporating
dish and weigh it to the
nearest 0.1 mg. Place it on a steam bath in a hood and add the
perchloroethylene to be tested by pipet in two 50-ml portions.
Perchloroethylene has a high specific gravity, 1.62, and is difficult
to handle
in a 100-ml pipet. Add the second portion after the first is partially
evaporated.
After the solvent has
completely evaporated on the
steam bath, heat the dish further in an oven at 105°C for 1 hr, then
cool it in
a desiccator and weigh. The increase in weight of the dish in grams for
a
100-ml sample is % nonvolatile residue.
Stability
Test.
Perchloroethylene is stabilized by adding traces of chemicals known to
inhibit
its decomposition. Loss of stabilizer or the presence of certain
impurities can
lower the stability of the solvent.
Procedure
Wash two strips of copper
foil, 2.0 X 7.5 X 0.005
cm, in concentrated hydrochloric acid. Rinse, dry, and weigh to the
nearest 0.1
mg. Add 75 ml of the test solvent and 3 ml of water to a 300-ml Soxhlet
extractor. Place one copper strip in the flask and the other into the
condenser
of the Soxhlet. Heat the Soxhlet at a rate that will cause it to empty
every
8-10 min.
After 24 hr, remove the
strips, wash them again in
concentrated hydrochloric acid, and weigh. The combined weight loss of
the two
strips should not exceed 30 mg.
Note:
Do not fail to add
the water with the solvent. The test is worthless in the absence of
water.
Fluorocarbon Solvent
Around 1960, Du Pont
introduced
trichlorotrifluoroethane as a drycleaning solvent under the trade name
Valclene. This solvent has aroused much interest because of its ideal
properties, but it is too volatile to be used in machines designed for
perchloroethylene. Therefore, its full utilization must a wait machine
development. A number of companies have introduced small machines for
the
solvent, but it will be several years; before use of the solvent is
widespread.
No special specifications or
test methods have been
developed for this solvent.
Used Drycleaning Solvents
In addition to the tests
given under the
specifications, there are several analytical methods designed for
quality-control purposes in practical drycleaning operations. These
methods are
normally performed on used solvent taken from plant washers. The
following
tests are made routinely on used solvent.
Detergent
Concentration.
The method of Fessler for anionic detergents is used. It is described
on. There
is no satisfactory method for drycleaning detergents that are all
nonionic;
however, manufacturers of nonionic detergent formulations normally
include some
anionie surfactant in the mixture to serve as a tracer. This serves the
purpose
of quality control with a known product but not for analysis of an
unknown
mixture.
Nonvolatile Residue.
This test is carried out by the
procedure except that 10 ml samples are used instead of 100 ml
Moisture
Content. The
moisture content of the used solvent can be determined by the Karl
Fischer method.
Acid
Number. This test was
originally designed to measure the buildup of fatty acids in the
solvent. Its
value has diminished in recent years because of the widespread use of
amine
sulfonate detergents. These detergents react quantitatively with the
titrant
giving a high value for the fatty acid content of the solvent. However,
the
test is still useful for control purposes where proper correction can
be
applied for interference by the detergent.
In other fields, acid number
is defined as the mg of
potassium hydroxide necessary to neutralize 1 g of sample. In
drycleaning, the
NID has defined acid number as the mg of potassium hydroxide necessary
to
neutralize 1.28 ml of solvent.
The titration is made in the
usual manner using a
0.06 N alcoholic solution of potassium hydroxide and phenolphthalein
indicator.
It was found that 2-methyl-2,4-pentanediol is a better solvent than
ethanol
because of its solubility in petroleum solvents.
Color.
The color of used
drycleaning solvents may be due chiefly to dyes dissolved from the
textiles.
The balance is caused by colored soils, or colloidally suspended
pigments. The
latter are removed by micro filtration prior to determining color. At
NID,
color is determined on a Coleman universal spectrophotometer using a
40-mm cuvet
at 500 nm. The instrument is standardized against water.
Greying
of Cotton. The
cotton fabric used for the residual odor test is read on the
reflectometer to
determine the decrease in % green reflectance. Although this is called
“greying†it is actually a measure of the amount of dye and other
colored
impurities dissolved in the solvent because the insoluble material has
been
removed by microfiltration through 0.2 µm membranes.
Sizing.
Many drycleaners
use certain resins in the solvent as sizes or bodying agents for
fabrics to
replace the finishing materials removed during wear or cleaning.
Natural
terpene resins are widely used and the amount of resin in the solvent
is
determined at NID by extracting the nonvolatile residue with boiling
ethanol.
This reagent dissolves everything except the terpene resins. The
procedure has
not been validated, however, for all types of sizes.
Suspended
Solids. After
microfiltration of a measured volume of the solvent, the membrane,
which has
been previously weighed, is oven dried at 105ºC and weighed to
determine the
quantity of insoluble material suspended in the solvent. The NID
standard for
this is 50 mg/liter. Larger quantities can cause excessive greying of
white
fabrics and is an indication of poor solvent filtration.
Drycleaning Detergents
Detergency
in nonaqueous solvents
follows much the same principles as in water, particularly in the
removal of
insoluble soil. The major differences come in the attack on
water-soluble and
solvent-soluble soils. In aqueous detergency the major attack is on the
oily
soils because the water-soluble soils are removed by simple solution.
In
drycleaning, on the other hand, the major attack by detergents is on
the
water-soluble soil because the oily soil is removed by simple solution.
In both laundering and
drycleaning, the processes of
emulsification and solubilization effect the removal of soil from the
fiber
surface. In both types of cleaning the detergents used are based on
surface
active agents.
Laundry detergents generally
contain not, more than
20% surface active agents (surfactants), the balance being various
types of
builders. Drycleaning detergents may consist of a single surfactant.
The
product may also contain a cosolvent or coupling agent to enhance the
capacity
for dissolving or emulsifying water and a fluorescent whitening agent.
Frequently, two or more surfactants are mixed.
A drycleaning detergent
performs three functions in
the cleaning process. It acts as a dispersant or peptizing agent for
insoluble
soils. It not only disperses this kind of soil, but also keeps it in
suspension. While it is being flushed out of the fabric and pumped to
the
filter. Insoluble soils may be dispersed to particle sizes in the
submicron
range by good detergents, and while so dispersed the particles of soil
are
small enough to escape between the tightly packed fibers in textile
yarns. In
the absence of a good detergent, this kind of soil is difficult to
remove and
readily redeposits on other fiber surfaces causing what is generally
called
greying, a phenomenon also common in laundering, particularly with
polyester
fibers. Thus, the first two roles of a drycleaning detergent are to
assist in
the removal of insoluble soil and to prevent it from redepositing on
other
fabrics in the bath.
The third function of a
drycleaning detergent is to
emulsify water in the solvent and promote the removal of water-soluble
soil by
the emulsified or solubilized water. Although the water plays the major
role in
detaching water-soluble soil from the fiber surface, the detergent
itself can
dissolve some of these soils within its micelles.
Progress in the formulation
of drycleaning
detergents is slow compared to the formulation of laundry detergents.
One
reason for the lack of progress has been the absence of reliable test,
methods
for drycleaning detergents. The literature on drycleaning detergent
test
methods is scanty and the few methods that have been described have
received
little attention or use. The methods described here have been in use at
the
National Institute of Drycleaning and are designed to test the ability
of a
detergent to perform its three functions.
Methods of Analysis
The tests to be carried out
on drycleaning
detergents can be divided into two groups: specification tests
resulting in
information on the properties of the detergents, and performance tests.
Specification Tests
Physical
Composition.
Drycleaning detergents, almost without exception, are liquids, so it is
desirable to know how much of the material consists of an active
ingredient and
how much is solvent or water. The determination is made on a
perchloroethylene
solution of known concentration of the detergent. An aliquot is
evaporated to
dryness as described on p. 608 for the determination of the nonvolatile
residue
of a solvent. The amount of water is determined on a separate sample by
the
Karl Fischer titration.
Some drycleaning detergents
are diluted with mineral
oil so that the nonvolatile residue is not all surfactant, but it still
establishes the upper limit of surfactant concentration.
Specific
Gravity. The main
purpose of this test is to establish what types of solvents are used as
diluents. Most surfactants have specific gravities close to unity,
whereas
drycleaning solvents have a specific gravity of about 0.8 (Stoddard
solvent) or
1.62 (perchloroethylene). The determination can be carried out by any
of the
conventional methods.
pH.
A drycleaning
detergent should be essentially neutral because of the adverse effect
of acids
and alkalis on some types of dyes. The test is made by thoroughly
shaking the
detergent with water and determining the pH of the water phase.
Distillation
Test. Since
used drycleaning solvent is reclaimed by distillation, it is important
that the
detergent cause no problems in the still. This is checked qualitatively
by
distilling a 1% solution of the detergent in perchloroethylene in an
all-glass
laboratory still. The process is observed for any signs of foaming,
flooding
over, or decomposition. The distillate should be pure
perchloroethylene;
presence of other volatile solvents is undesirable.
Detergents intended for use
in Stoddard solvent must
be tested by vaccum distilling a 1% solution in this solvent.
Solubility
in Drycleaning
Solvents. The purpose of this test is to ascertain that the
detergent is
soluble in both solvents. A simple qualitative test is sufficient.
Chemical
Type. It is
desirable to know whether the surfactant in the detergent is anionic,
cationic,
nonionic, or a mixture of ionic and nonionic surfactants. This can
be’determined by studying the infrared spectrum of the sample as well
as the
methylene blue titration method given below.
Detergent
Concentration by
Methylene Blue Titration. This method is widely used as a
control test to
determine the amount of a particular detergent in a drycleaning
solution. It
was originally described by Fessler, in 1951. The following procedure
is from
an NID publication.
Procedure
Anionic
Surfactants. Place
25 ml of chloroform into a 100-ml glass-stoppered graduated cylinder.
Take at
least a 5-ml sample of the solution to be tested, dilute to 100 ml, and
then
add a proper .aliquot to the chloroform. Add 25 ml of water containing
1 drop
of a 0.5% methylene blue solution and shake. The methylene blue enters
the
chloroform layer as a result of solubilization by the surfactants.
Start to add
a 0.02% aqueous cetylpyridinium chloride solution in 0.5 ml increments
and
shake the mixture vigorously after each addtion. As long as any free
anionic
surfactant remains in the chloroform layer. Eventually this is complete
and the
lower layer is colorless. A sharp and reproducible end point is the
point of
equal color distribution between the two phases. Prepare a calibration
curve
for each detergent by titrating a number of samples of known
volume-volume
concentration over the expected range and plotting ml of titrant
against
detergent concentration.
Cationic Surfactants. Carry
out the determination in
a similar way but by using a standard anionic surfactant such as Aersol
OT as
the titrant.
Nonionic surfactants cannot be
titrated in this manner.
However, detergents consisting of nonionic surfactants generally
contain a
small amount of anionic surfactant, as a tracer so the solution can be
titrated
to control concentration.
Acid
Number. One of the
most widely used types of drycleaning detergents is classified as amine
sulfonate. When solutions of amine sulfonates are titrated by alcoholic
potassium hydroxide as in the usual acid number determination they
hydrolyze
and the sulfonic acid titrates as if it were a fatty acid. Thus, this
titration
gives information of the relative quantities of this type of surfactant
present.
If the composition of the
detergent, is known to be
amine sulfonate, this determination provides a more rapid and
convenient method
of analysis than the methylen blue titration.
Water-Holding
Capacity.
This is the most important specification test to be made on drycleaning
detergents because performance tests cannot be carried out without this
information.
To understand the method, it
is necessary to know
something of the moisture relations in a drycleaning bath between a
detergent
solution, a textile immersed in it, and the atmosphere in equilibrium
with the
solvent phase. Briefly, the solution dissolves water within the
detergent
micelles which retard evaporation and lower the water vapor pressure
over the
solution. Eventually, the solution comes to moisture equilibrium with
the
immersed textile and the atmosphere over the solution. At equilibrium,
the
water vapor pressure in all three phases must be equal. If the relative
humidity
in the vapor phase is 75% then the solution is said to have a solvent
relative
humidity of 75%. At this condition the immersed textile will have the
same
regain or absorbed moisture content as it would have at equilibrium in
the
vapor phase at 75% relative humidity.
The NID defines the
water-holding capacity as %
water in a 1% detergent solution measured at a solvent relative
humidity of
75%.
The amount of water in both
the solvent and textile
is determined by a Karl Fischer titration whereas the relative humidity
of the
vapor phase is measured with Dunmore-type humidity sensors.
It is the usual practice to
determine the moisture
content of a series of 1% solutions of the detergent at various solvent
relative humidity values, and to plot the data to obtain a moisture
content vs
relative humidity curve for the detergent. The curve permits the
estimation of
the solvent relative humidity of any solution of that detergent by a
Karl
Fischer titration (giving the amount of water) plus a methylene blue
titration
(giving the amount of detergent). It should be noted that the solvent
relative
humidity depends only on the ratio of water to detergent in the
solution. Hence
if a 1% solution of a particular detergent contains 0.07% water at 75%
relative
humidity, then a 2% solution will contain 0.14% water at the same
relative
humidity.
Light
Transmittance. This
value is an index of the degree of clarity of a 1% (v/v) solution of
the
detergent. The transmittance is normally measured at 450 and 500 nm,
the most
sensitive region for yellow or amber-colored products.
In some cases, the color is
due to solubilized
impurities such as iron oxide, which can deposit on fabrics. The
solution is
tested for this possibility by immersing a white cotton fabric of about
94%
reflectance, green filter, into the solution. After removal and air
drying, the
reflectance is again measured. A loss of reflectance of more than 4%
(i.e., a
reflectance below 90%) is considered excessive.
Performance Tests
Two performance tests are
usually carried out, a
test for insoluble soil removal and redeposition control, and a test
for
water-soluble soil removal.
Insoluble Soil Removal and
Redeposition Control.
The ability of a drycleaning detergent to remove insoluble soil and to
prevent
that soil from redeposition on another fabric is tested by adding
soiled and
unsoiled swatches of cotton fabric to a test solution of the detergent
in a
Launder-Ometer or in aTerg-O-Tometer. These are machines with
thermostatically
controlled water baths and oscillating type agitators. The Terg-O-
Tometer has
an oscillating agitator but the Launder-Ometer uses rotating canisters.
They
may be purchased from the following companies: (a) Launder-Ometer,
Atlas
Electric Devices, 4114 N. Ravenswood Ave., Chicago, Ill.; (b)
Terg-O-Tometer,
U.S. Testing Co., 1414 Park Ave., Hoboken, N.J. The reflectance of the
cotton
swatches is taken before and after the cleaning operation, and the
detergent
formulations are rated with a reference detergent having only mediocre
cleaning
ability. The reference detergent is Aerosol OT, sodium di(ethylhexyl)
sulfosuccinate, long used as a standard detergent in drycleaning
research
because of its chemical purity: it is available in 99+% active grade.
Test
conditions deliberately overwhelm the reference detergent so that the
superiority of the test detergents will be readily manifested.
The insoluble soiling
material is applied to the
test swatches so that the particles are fully dispersed. If this is not
done,
reflectance measurements are not accurate. If wet soiling methods are
used, a
dispersing agent is used and subsequently rinsed out, or the pigment
material
is mechanically dispersed in oil with a mortar and pestle or ball mill.
Before
testing, the soiled and unsoiled swatches are conditioned at 75%
relative
humidity for several days at 70±5°F. A desiccator over a saturated
sodium
chloride solution may be used or the test can be standardized on the
basis of
65% relative humidity and 70°F, the standard textile testing laboratory
conditions, in a constant temperature-humidity room.
Aerosol OT is slow to
dissolve in drycleaning
solvent, so a stock solution of known concentration should be prepared
and
aliquots taken and diluted to 1% for use in the test. Solvent used in
the test
should be prefiltered through a 0.2 µm Millipore filter.
Procedure
Determine the reflectance of
all 4 X 4 in. swatches,
using the green filter. Use the blue filter also if yellowness changes
are
desired. Run all tests in duplicate using a Launder-Ometer equipped
with 500-ml
stainless steel canister. Add 150 ml of the detergent solutions to each
canister, then add thirty ¼ in. stainless steel balls.
Use three clean and three
soiled swatches for each
canister. Add clean and soiled swatches alternately, crumpling each
slightly to
prevent them from adhering and to improve the agreement of the
replicates.
Run the Launder-Ometer for 1
hr at 25±1°C to reach
equilibrium.
Empty the canisters into 10
cm diameter Buchner
funnels to drain away solvent. With forceps take each swatch by a
corner and
dip it rapidly ten times into two successive rinse baths of 300 ml of
filtered
perchloroethylene. Use clean rinse solvent in both beakers for each
canister.
Lay the rinsed swatches on a
blotter paper, cover
them with another blotter paper, and dry overnight at room temperature.
Read the reflectances of each
swatch as before and
calculate the averages for each detergent. Compute the average change
in
reflectance of both the soiled and unsoiled swatches for each detergent
being
tested and for the reference detergent.
The ratio of reflectance
change (DR) for each
detergent to that of the reference detergent gives an index number
permitting
comparison of test data made at different time or under slightly
different
conditions.
The ratio of the unsoiled
swatch reflectance changes
is called the greying index and that of the soiled fabrics is the
cleaning
index. The lower the greying index and the higher the cleaning index,
the
better the detergent.
The most critical operations
of this test are the
reflectance readings, the addition of swatches, and rinsing.
Reflectance readings can vary
with the instrument
and the fabric construction. With the 45/0 geometry of the Gardner
Precision
reflectometer, twelve thicknesses of new cloth, or six of soiled, are
sufficient to exclude the background. Big differences could affect
readings
through one thickness, so each subgroup should be kept together and
rotated
only within itself. Thus, for each set of two canisters, the twelve
swatches
are placed in a pack and rotated so that each swatch is always backed
by eleven
others. The five swatches immediately behind the one being read must be
similar
to it; that is, the six redeposition swatches have to be kept together.
Readings of warp vertical and warp horizontal from both front and back
must be
averaged with this instrument. Instruments with spherical optics
require only
one reading on each side.
If the swatches are added
alternately, one clean and
one soiled, both the redeposition and cleaned groups will show little
variation
within themselves or between canisters.
Rinsing is only meant to
remove the large, loosely
attached particles. Quick motions and rinsing each swatch separately
leaves
very little if any on the swatches.
Several specifications in the
procedure are not
critical. For example, the moisture content is not a particularly
sensitive
variable in this test. However, it is sound test practice to control
this
variable if possible. The 1 hr running time is another arbitrarily
fixed
variable. This time was selected to give the samples every chance to
equilibrate. A powerful detergent can bring the system to equilibrium
earlier;
equilibrium exists when all six swatches show the same reflectance. If
a
Terg-O-Tometer is used, the running time should be shorter, only 30
min, because
of the greater mechanical action in this instrument. Also, evaporation
losses
may be serious from the open beaker of the Terg-O-Tometer in 1 hr.
The purpose of the yellowness
measurement is to
detect any effect due to an optical brightener in the formulation.
Under these test conditions,
some soil will also
redeposit on the soiled swatches. If it is desired to measure the
specific soil
removal, independently of greying, a much higher solvent volume needs
to be
used to minimize soil redeposition.
The procedure detailed above
can be adapted to any
type of standard soiled fabric suitable for use in a drycleaning
solvent and
soiled with a formula containing a high percentage of insoluble soil.
The NID has arbitrarily
chosen to test detergents at
the 1% (v/v) concentration level because this is the most frequently
used
concentration in drycleaning plants. Some products perform about as
well at
0.25% as at higher concentrations; others require concentrations higher
than 1%
to exhibit their best performance. The test procedure is adaptable for
studying
concentration, solvent relative humidity, and other factors that are
fixed in
the procedure.
Water-Soluble
Soil Removal.
The NID has long used rayon fabrics impregnated with sodium chloride or
with
glucose to measure water-soluble soil removal in a drycleaning machine.
These
model soils are satisfactory for large-scale tests but difficult to
reduce to a
laboratory scale due to moisture exchange between detergent solution,
rayon,
and salt or glucose. They will interact until three-way equilibrium in
water
vapor pressure is reached. If the solvent relative humidity drops to
65% or
below, little or no salt or glucose can be removed. The equilibrium can
be
controlled at a higher relative humidity level in a machine without
difficulty,
but not in small-scale laboratory tests unless the test work is done in
a
constant temperature and humidity room. Not only will the fabric absorb
moisture from the solvent, lowering its relative humidity, but the salt
or
glucose on the fabrics will absorb moisture. Salt is particularly
trouble some
because it does not attain equilibrium quickly with dissolved moisture
but
continues to pick up water until each crystal is surrounded by a
droplet of
liquid water.
The method used at NID and
described below avoids
the problem by using a polyester fabric that does not absorb moisture,
and a
water-soluble dye as a model soil. The amount of dye on the fabric is
so small
that it, cannot remove a measurable quantity of water from the solution.
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