Process to make soap

A process for producing soap which comprises blending soaps, water, and glycerin prepared from PA1 a. the neutralization of at least one free fatty acid with a strong alkali to produce soap and water, and PA1 b. the saponification of at least one triglyceride with a strong alkali to produce soap and glycerin, the amount of glycerin from step b being sufficient to provide up to about 6 wt. % of glycerin to the finished soap product. A process for producing soap from a mixed feedstock of at least one triglyceride and at least one free fatty acid which comprises contacting at least one triglyceride and at least one free fatty acid with strong alkali at an elevated temperature, the quantity of triglyceride present so that the glycerine produced from its saponification with strong alkali does not exceed about 6 wt. % of the finished soap product.

BACKGROUND OF THE INVENTION 
Soaps have been utilized for years to remove soil from surfaces. Various 
processes have been used to produce soap. Generally, the two most 
preferred starting materials are triglycerides which are saponified into 
soap and free-fatty acids which are neutralized into soaps. Saponification 
of the triglyceride is usually performed in an open kettle at a 
temperature of from about 215-220.degree. F. over a long period of time, 
several hours. Alternatively, the saponification is carried out in a 
continuous closed systems at super atmospheric pressure and a temperature 
of about 250.degree. F. Fatty acid neutralization is usually not carried 
out in an open kettle because of oxidation problems. It is usually 
performed in a closed system at atmospheric pressure and a temperature of 
about 195.degree. F. 
The invention of this application allows for both saponification and 
neutralization to occur simultaneously at a temperature not generally 
achievable by saponification alone. This invention brings about 
significant cost savings, primarily realized from three avenues. Firstly, 
the price differential between the neutral oil or fat as opposed to the 
total use of fatty acids is substantial. Secondly, the in situ formation 
of glycerin negates the need to purchase glycerin and add such glycerin to 
soap made by neutralization alone. Thirdly, the mixed charge of 
triglyceride and fat allows the reaction to proceed at a lower temperature 
than is normally required for complete saponification of a total 
triglyceride feed charge. This provides for lower energy input as well as 
an additional cost advantage with respect to equipment purchase price 
since equipment rated for higher pressures and temperatures is not 
required. 
SUMMARY OF THE INVENTION 
In accordance with the invention, there is a process for producing soap 
which comprises blending soaps, water, and glycerin prepared from 
a. the neutralization of at least one free fatty acid with a strong alkali 
to produce soap and water, and 
b. the saponification of at least one triglyceride with a strong alkali to 
produce soap and glycerin, the amount of glycerin from step b being 
sufficient to provide up to about 6 wt. % of glycerin in the finished soap 
product. 
Further in accordance with the invention there is a process for producing 
soap from a mixed feedstock of at least one triglyceride and at least one 
free fatty acid which comprises contacting at least one triglyceride and 
at least one free fatty acid with strong alkali at an elevated 
temperature, the quantity of triglyceride present in an amount so that the 
glycerin produced from its saponification with strong alkali does not 
exceed about 6 wt. % of the finished soap product. 
DETAILED DESCRIPTION OF THE INVENTION 
The triglyceride utilized as a portion of the feedstock in the reactor is 
any triglyceride normally utilized in soap making. Examples of such 
triglycerides include those derived from coconut oil, palm kernel oil, 
palm stearin oil, palm oil, tallow, tallow olein, tallow stearin, soya, 
hydrogenated soya, babasu oil, fish oils, and the like. The saponification 
reaction with strong alkali produces glycerin as well as a soap having as 
the long chain alkyl grouping the long chain alkyl group from the 
triglyceride. It is well known that the saponification reaction does not 
proceed rapidly and has significant problems with respect to completion, 
particularly when triglycerides with longer alkyl groupings, for example, 
having a preponderance of C.sub.16 and C.sub.18 chains, are employed as 
opposed to those triglycerides with a preponderance of C.sub.12 and 
C.sub.14 chains. Examples of long chain triglycerides are those derived 
from tallow and palm oil. However, in this invention no significant 
difference in processing conditions is observed between a tallow derived 
triglyceride feedstock and a coconut oil derived triglyceride feedstock. 
The coconut oil has a predominance of C.sub.12 and C.sub.14 alkyl groups 
therein. Generally, the alkyl grouping of the triglyceride will have 
significant numbers, that is a preponderance, of alkyl groups in the 
C.sub.12 -C.sub.18 range. The alkyl groups are normal or branched, 
preferably normal. 
Free fatty acids which are employed in the reaction are those normally used 
in soaps, i.e., having a preponderance of C.sub.12 -C.sub.18 alkyl groups 
therein. The alkyl groups are normal or branched, preferably normal. 
Examples of such carboxylic acids includes lauric, myristic, palmitic, 
stearic and the like. The neutralization reaction with strong alkali is 
the classic neutralization of an acid with a base to form a salt (i.e. 
soap) and water. 
The strong alkali generally employed in the reaction is generally sodium 
hydroxide or potassium hydroxide. However, it is preferred to use the 
alkali metal hydroxide, sodium hydroxide. 
Generally, the contents of the reactor can include triglyceride, free fatty 
acid, strong alkali and water, although it is preferable to have a small 
amount of salt such as sodium chloride in order to control the viscosity, 
provide finished product traits particularly in bar form, and assist in 
controlling the phases present in the reactor. 
The reactor which can be employed is any type of reactor used for fatty 
acid neutralization reactions. Generally, this is a stirred tank reactor 
which is preferably equipped with a high capacity recycle stream. There is 
generally at least a 5 to 1 recycle rate as measured by weight of 
recycling material to feed material. The hold-up time is usually a minimum 
of about 5 minutes in the reactor, preferably a minimum of about 10 or 
about 15 minutes. The maximum hold up time is primarily a matter of 
economics. Generally, hold up times of less than about 60 minutes, 
preferably less than about 45 minutes are employed. The temperature of the 
reaction is sufficient to complete the reaction. Generally, this is above 
about 180.degree. F. The maximum temperature is not unduly significant, 
but is specifically related to the potential loss of water in an open 
system, if that is used. Therefore, the temperature is generally not much 
above about 215.degree. F. It is preferable to maintain reaction 
temperatures of from about 190-210.degree. F. The actual temperatures 
clearly depend upon the desired residence time, hold-up time, in the 
reactor. The strong alkali, preferably sodium hydroxide is preferably 
employed at slightly greater than the actual stoichiometric amounts. This 
brings about a reaction which is driven to completion and avoids the 
triglyceride non-saponification which can lead to rancidification in the 
final solid product. The excess amount of alkali, i.e., sodium hydroxide 
above the actual stoichiometric amount, is utilized to drive the reaction 
to a level of unsaponified triglyceride which can no longer be measured by 
conventional analytical means. 
Below is a specific analytical method which can be employed for this 
measurement. The amount of unsaponified oils in a soap sample are 
indirectly measured due to the presence of other oils which are 
unsaponifiable. These unsaponifiable oils remain unreacted throughout the 
cosaponification reaction and cannot be easily separated from the 
unsaponified oils. The amount of unsaponified oils are determined by 
difference. The total of unsaponified plus unsaponifiable oils in a sample 
of soap, known as U+U, is measured in one analysis, and the amount of 
unsaponifiable oils is measured in another analysis. The difference is the 
amount of unsaponified oils. Due to the complexity of this analysis, which 
involves multiple transfers of the solutions being analyzed, there is a 
degree of error which cannot be overcome. From experience, if the final 
difference of the quantity % U+U minus the % unsaponifiable amount is in 
the range of about +/-0.05%, the unsaponified amount is considered to be 
zero. 
The analytical procedure is as follows. A sample of soap, about 8 to 10 
grams, to be analyzed is weighed and dissolved in 300 ml of a 1:1 by 
volume mixture of distilled water and denatured alcohol. The solution is 
made slightly acidic and may be heated to facilitate dissolving. When 
fully dissolved, the mixture is made alkaline with NaOH to phenolphthalein 
color. It is then extracted with 100 ml of a solvent mixture of pentane 
isomers (hexane may also be used), by shaking them together in a flask. 
After the solvent separates, it is removed and saved. This extraction is 
done three or four times depending on the efficiency of separation. The 
total quantity of solvent removed from the three or four extractions is 
combined and washed three times with 10 to 15 ml of denatured alcohol each 
time to remove any fatty acids which may have been extracted. The washed 
pentane solvent is transferred to a tared flask and completely distilled 
off. The residual free oil left in the flask after distilling off the 
solvent is quantified by weighing to four-place accuracy on an analytical 
balance. It is then expressed as a percent of the starting weight of soap. 
This percent is the total amount of unsaponified and unsaponifiable oils, 
U+U. 
To determine the amount of unsaponified oil, the amount of unsaponifiable 
oil is measured and subtracted from the total of U+U. The amount of 
unsaponifiable oil is measured by heating and reacting the sample in a 
strong caustic environment for about 20 minutes to fully saponify any 
unsaponified oils first. The sample will then contain only unsaponifiable 
oils and is analyzed by pentane extraction as described above to determine 
the amount of unsaponifiable oils present. This analysis may be done on 
the same sample for which the U+U was determined, by redissolving the 
residual oil in a 1:1 water and alcohol mixture and reacting it prior to 
re-extraction, or a fresh sample of the same soap may be used. 
For the invention process, in practice, the excess caustic concentration 
can amount to about 0.05 wt. % of the total reaction mass above the actual 
stoichiometric amount calculated for the reaction feed materials. 
Preferably, it is about 0.1 wt. % or higher. The major factor for 
determining the maximum amount of alkali coverage is primarily dependent 
upon the cost of the material. However, large amounts of alkali overage 
can begin to affect the final pH of the soap product as well. Therefore, 
no more than about 0.2 wt. % alkali excess is generally employed. 
As noted previously, this particular invention process results in the 
presence of glycerin in the final soap product, such glycerin prepared in 
situ during the triglyceride saponification. Because of various handling 
problems as well as undesired plasticity, it is usual to not have more 
than about 6 wt. % glycerin in the final product. A 6 wt. % glycerin 
content will generally bring about a relatively translucent and plastic 
bar. Generally, no more than about 2.5 wt. % glycerin is desirable, 
preferably no more than about 2 wt. %. Assuming that all the glycerin 
comes from the triglyceride saponification, the wt. % of triglyceride 
present in the reactor is specifically related to the amount of glycerin 
that one wishes to have in the final soap product. The quantity of 
triglyceride can differ due to the quantity of glycerin present in the 
particular triglyceride. For example, a coconut oil based triglyceride has 
about 14 wt. % glycerine in the triglyceride while a tallow based 
triglyceride has about 10 wt. % glycerine in the triglyceride. Generally, 
about 18 to about 25 wt. % of the charge of triglyceride and free fatty 
acid is triglyceride. The specific quantity of triglyceride employed is 
dependent upon the quantity of glycerin desired in the final product and 
the source of the triglyceride. A shaped solid product such as a hand-held 
bar is most preferred. 
The reaction can proceed in either a batch or continuous manner. The 
temperatures are such that an open system can be employed, particularly in 
the batch procedure. However, for a continuous process, it is generally 
preferred to have some pressure on the system, at least to bring about the 
circulation of the materials within a closed loop. The pressures which can 
be employed can vary from about 5 psig to whatever pressure is desired. 
Generally, pressures of less than about 100 psig can be employed. Pressure 
is generally not a significant variable in this process. Exact pressures 
are determined by the design of the equipment, particularly the pumps. 
Clearly, mixing is of some significance so as to provide at least minimum 
contact of the reactants. A steady, essentially isothermal temperature 
controlled reaction is desirable and readily obtained. 
As noted, it is preferable to do the reaction in one reactor. However, if 
one wishes to, one can run each one of the reactions, i.e., the 
saponification and neutralization reactions, each in a separate reactor or 
sequentially in the reactor and combine the products thereafter to form 
the same composition as would be formed in the preferred method of 
reaction in a single reactor.

Below are examples of the invention. These examples are not intended to 
narrow the invention, but are used to exemplify the broad nature and scope 
of the invention. All the analyses for unsaponified oil are conducted by 
the method previously described in the specification. 
EXAMPLE 1 
A stainless steel reactor system composed of a centrifugal pump in a 
recycle loop with a heat exchanger and a flow-through holding vessel is 
used to produce a cosaponified soap product from refined, bleached, and 
deodorized palm kernel oil and a fatty acid blend of tallow and coconut 
fatty acids. The reaction is carried out in a continuous fashion with 
three accurately weight-metered feed streams being continuously fed: the 
fatty acid blend, the refined, bleached, and deodorized palm kernel oil, 
and a lye, which is an aqueous solution of sodium hydroxide and sodium 
chloride. These three streams are fed into the inlet of the centrifugal 
pump along with the returning bulk recycle stream to provide for good 
mixing of the feed ingredients. After a start-up period to bring the 
reactor system to steady state, the soap product is continuously drawn out 
of the recycle loop through a back-pressure valve. The temperature of the 
reactor is maintained by the heat of reaction and controlled by tempered 
cooling water in the recycle loop heat exchanger. The total quantity of 
soap held up as it is recycling in the reactor system is 25 lbs. 
The fatty acid blend of 74.2% tallow fatty acid and 25.8% coconut fatty 
acid, having an acid value of 223.5 gm KOH/kg fatty acid, is fed at a rate 
of 20.8 lbs/hr; the refined, bleached, and deodorized palm kernel oil, 
having a saponification value of 251 gm KOH/kg oil, is fed at a rate of 
5.17 lbs/hr; and the lye, with concentrations of 26.6% sodium hydroxide 
and 1.56% sodium chloride, is fed at a rate of 15.9 lbs/hr. These rates 
and concentrations provide an average reaction residence time of 35.8 
minutes and the stoichiometric proportions necessary to neutralize the 
fatty acids, to saponify completely the refined, bleached, and deodorized 
palm kernel oil, to leave a residual concentration of sodium hydroxide of 
0.1% in the soap product, and to produce a soap product having a 60/40 
tallow/coco fatty acid ratio with 1.7% glycerin (about 2.0% glycerin in 
the final soap bar product after addition of finishing ingredients and 
drying to 10% moisture), 0.6% sodium chloride, and 30.7% water. The 
reaction is carried out at a temperature of 200.degree. F., with a system 
pressure of 35 to 45 psig at the inlet and 60 to 70 psig at the outlet of 
the centrifugal pump. Five samples of the final product were analyzed to 
contain 0.0 to 0.015% unsaponified free neutral oil. 
EXAMPLE 2 
A process is run as described in Example 1, but where the residence time of 
the reactor system is 15 minutes, the temperature is in the range of 195 
to 205.degree. F., and the residual sodium hydroxide is in the range of 
0.1 to 0.2%. The feed materials and flow rates are as follows. The fatty 
acid blend of 72.6% tallow fatty acid and 27.4% coconut fatty acid, having 
an acid value of 222.4 gm KOH/kg fatty acid, is fed at a rate of 49.98 
lbs/hr; the refined, bleached, and deodorized palm kernel oil, having a 
saponification value of 248.8 gm KOH/kg oil, is fed at a rate of 11.03 
lbs/hr; and the lye, with concentrations of 25.27% sodium hydroxide and 
1.58% sodium chloride, is fed at a rate of 38.2 to 38.6 lbs/hr. These 
rates and concentrations provide an average reaction residence time of 15 
minutes and the stoichiometric proportions necessary to neutralize the 
fatty acids, to saponify completely the refined, bleached, and deodorized 
palm kernel oil, to leave residual concentrations of sodium hydroxide of 
0.1% and 0.2% in the soap product, and to produce a soap product having a 
60/40 tallow/coco fatty acid ratio with 1.5% glycerin (about 2.0% glycerin 
in the final soap bar product after addition of finishing ingredients and 
drying to 10% moisture), 0.6% sodium chloride, and 31.6% water. The 
reaction is carried out at temperatures of 195.degree. F. and 205.degree. 
F. for both levels of residual sodium hydroxide, with a system pressure of 
35 to 45 psig at the inlet and 60 to 70 psig at the outlet of the 
centrifugal pump. Samples of the final product were analyzed to contain 
0.01% to 0.05% unsaponified free neutral oil. 
EXAMPLE 3 
A process is run as described in Example 1, but with the neutral oil being 
refined, bleached, and deodorized coconut oil. The feed materials and flow 
rates are as follows. The fatty acid blend of 74% tallow fatty acid and 
26% coconut fatty acid, having an acid value of 228.4 gm KOH/kg fatty 
acid, is fed at a rate of 20.35 lbs/hr; the refined, bleached, and 
deodorized coconut oil, having a saponification value of 253 gm KOH/kg 
oil, is fed at a rate of 5.02 lbs/hr; and the lye, with concentrations of 
26.16% sodium hydroxide and 1.53% sodium chloride, is fed at a rate of 
15.78 lbs/hr. These rates and concentrations provide an average reaction 
residence time of 36.45 minutes and the stoichiometric proportions 
necessary to neutralize the fatty acids, to saponify completely the 
refined, bleached, and deodorized coconut oil, to leave a residual 
concentration of sodium hydroxide of 0.1% in the soap product, and to 
produce a soap product having a 60/40 tallow/coco fatty acid ratio with 
1.69% glycerin (about 2.0% glycerin in the final soap bar product after 
addition of finishing ingredients and drying to 10% moisture), 0.6% sodium 
chloride, and 31.2% water. The reaction is carried out at a temperature of 
200.degree. F., with a system pressure of 35 to 45 psig at the inlet and 
55 to 65 psig at the outlet of the centrifugal pump. Samples of the final 
product were analyzed to contain 0.0% to 0.04% unsaponified oil. 
EXAMPLE 4 
A process is run as described in Example 1, but with edible tallow being 
substituted for the refined, bleached, and deodorized palm kernel oil. The 
feed materials and flow rates are as follows. The fatty acid blend of 
47.3% tallow fatty acid and 52.7% coconut fatty acid, having an acid value 
of 238.9 gm KOH/kg fatty acid, is fed at a rate of 19.25 lbs/hr; the 
edible tallow, having a saponification value of 196.2 gm KOH/kg tallow, is 
fed at a rate of 6.41 lbs/hr; and the lye, with concentrations of 26.86% 
sodium hydroxide and 1.56% sodium chloride, is fed at a rate of 15.68 
lbs/hr. These rates and concentrations provide an average reaction 
residence time of 36.28 minutes and the stoichiometric proportions 
necessary to neutralize the fatty acids, to saponify completely the edible 
tallow, to leave a residual concentration of sodium hydroxide of 0.12% in 
the soap product, and to produce a soap product having a 60/40 tallow/coco 
fatty acid ratio with 1.66% glycerin (about 2.0% glycerin in the final 
soap bar product after addition of finishing ingredients and drying to 10% 
moisture), 0.6% sodium chloride, and 31.2% water. The reaction is carried 
out at a temperature of 200.degree. F., with a system pressure of 30 to 45 
psig at the inlet and 60 to 70 psig at the outlet of the centrifugal pump. 
Samples of the final product were analyzed to contain 0.0% unsaponified 
tallow. 
All of the specific examples relate to preparation of a solid soap product, 
the preferred bar. However, the process is also applicable to liquid soap 
products as well.