Manufacture of Soap From Fatty Acids
Manufacture of Soap From Fatty Acids
Manufacture of Soap From Fatty Acids
OAP MANUFACTURE via the f a t t y acid route has been splitter and auxiliary equipment is whether a catalyst
S practical only since the development of con-
tinuous fat-splitting equipment of the countercurrent
is to be used or not. The catalyst most often em-
ployed in commercial splitters is zinc oxide. Others
type in the 1930's and 1940's by workers at Colgate- tried include NaOtt, KOH, LiOH, MgO,Ca(OH2).
Palmolive-Peet Company, E m e r y Industries, and The zinc catalyst is converted to zinc soaps before
Procter and Gamble (1,2,3). the fat enters the splitter. This catalyst was found by
The two general methods of making soap, 1) direct Lascaray (8) and was the most effective one tried.
saponification of fat and 2) fat splitting followed b y The f u n c t i o n of this catalyst is to assist in emulsifying
distillation and saponification, both have some ad- the triglyceride oil with water to permit the hydrolysis
vantages and disadvantages. The many features of to begin without the lengthy induction period other-
direct saponification of triglycerides by batch and wise required. When a certain amount of hydrolysis
continuous methods are covered by another paper (4) to f a t t y acid has occurred, the solubility is greatly
presented at this Short Course. increased and the reaction proceeds rapidly.
I t is the purpose os this paper to describe the proc- I f a catalyst is employed, additional equipment is
esses and equipment involved in manufacturing soap required to mix the zinc oxide with the fat and get
from fats via f a t t y acids in some detail, and to it into solution before the fat enters the splitter, and
discuss the advantages and disadvantages of the var- also to remove it from still bottoms after distillation.
ious soap making procedures. A simplified schematic Without a catalyst, a larger splitter is required to
diagram of the process being described is shown in obtain the same rate of t h r o u g h p u t at the equivalent
F i g u r e 1. extent of reaction (97-99% split). Since other aux-
JFAT !Z l
Essentially, the hydrolysis of triglycerides to f a t t y
acids and glycerine by reaction of water and fat u n d e r REFINED
FATTY
conditions of high temperature and pressure is a WATER - -
simple chemical process. To obtain high yields of f a t t y
acids, the reverse reaction in the equilibrium must be
repressed by countereurrent washing to remove the
glycerine from the reaction zone. A simple diagram
of a fat splitter is shown in F i g u r e 2. The rate of DRY SOAP
An important feature in the design of the fat Fie. 1. Schematic diagram of fatty acid route to soap.
616 THE JOURNAL OF THE AMERICAN 0 I L CttE)s SOCIETY VoL. 40
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HE SULFONATIONof alkyl benzene and the sulfation The next stage in the development of the sulfona-
T of f a t t y alcohol have been under continuous study
not only by the detergent manufacturers, but also
tion process was that of continuous processing rather
than batch. Here the only advantages were possibly
by the suppliers of detergent manufacturing equip- lower plant costs and lower operating costs, since there
ment and of detergent raw materials. was not any improvement in product quality.
When detergents were first introduced to the market Later came High Active Ingredient (AI) which
they were generally in powder form and the active allowed the separation of the major portion of the
ingredients employed could contain large amounts of sulfuric acid present in the acid mix prior to neutrali-
sodium sulfate without presenting any undue prob- zation. P r o d u c t with an active content of 87-88%
lems. However, with the advent of the liquid prod- on a d r y basis can be produced by such a process.
ucts, active ingredients containing little inorganic B u t m a n y liquid formulas demanded still higher
salt were essential--and it is this fact which has active contents. The advent of stabilized liquid S0a
stimulated, to a major extent, the development work made it possible to economically prepare a product
on sulfonating with SOn rather than with oleum. with 96-97% AI on a d r y basis. The suppliers of
I think that it will be worth a few minutes of our this stabilized liquid S0a developed batch processes
time to follow briefly the development of the sulfona- which included the vaporization of the liquid S0a,
tion process so that we might better appreciate the diluting this with dried air to approximately 10% by
problems that had to be overcome to arrive at the volume, and contacting this gaseous stream with alkyl
present s t a g e - - t h a t is, sulfonation using gaseous S03 benzene previously weighed and placed in the reactor
produced directly from the burning of sulfur. tank. Although the use of liquid S03 has economic
Throughout this discussion keep several points in advantages over the use of oleum, it was the inability
mind: of this process to match the product quality produced
on the oleum plants that prevented it from being
1) P r o d u c t quality is the key to the acceptability readily accepted by the major detergent manufac-
of a process, and for alkyl benzene the specifica- turers. I t should be mentioned that there is one
tions are: 98% completion of reaction and a m a n u f a c t u r e r who claims to have a continuous process
white paste upon neutralization with the alkali. using vaporized S03 but there arc no details available
2) The color of the neutralized paste is good or on this.
bad depending upon the ability of the process There is another batch process operating today
to remove the heat of reaction instantaneously. which uses the technique of reacting liquid S03 with
3) The heat of reaction for the sulfonation in- alkyl benzene in the presence of liquid S 0 2 - - a n d
creases with increasing oleum s t r e n g t h s - - a n d conducting this reaction at very low temperatures.
is a maximum when S03 is used. The product produced by this process is excellent.
Mr. Morrisroe pioneered the commercial development
Thus it is easy to understand that the first produc- of this process.
tion units were batch plants and the sulfonating Now we come to the latest stage of development
agent was 10-20% oleum. In these plants the alkyl for the su]fonation r e a c t i o n - - a n d this is the burning
benzene was weighed and placed in a tank; then the of sulfur to produce the required S03 and coupling
oleum was slowly added until the quantity required this directly to the sulfonation reactors for continuous
by the formula was also placed into the tank. With operation.
the two reactants now intimately mixed, they were This combination of sulfur burning and sulfona-
now permitted to digest for 30-45 rain. After the tion has economic advantages and has been worked
digestion period the neutralization of this acid mix out to a high degree of precision by the Ing. Mario
was carried out. Ballestra Co. There are others who have followed
Continuing engineering development w o r k ~ t o more this type of processing and we will attempt to show
efficiently remove the heat of reaction at the point the basic differences between various processes.
of contact of the oleum with the alkyl benzene--soon Very few details are available concerning other proc-
permitted the use of 25% oleum. esses. Therefore our attempt to compare other opera-