Process for the preparation of fatty acid alkyl esters having improved processing properties

Lower alkyl esters of higher fatty acids with improved processing properties, particularly sulfonation, are obtained by subjecting lower alkyl esters of higher fatty acids of plant and/or animal origin, or said fatty acids per se, in the presence of esterification catalysts and/or carboxylic acid anhydrides, to a brief temperature treatment above 150.degree. C., and separating simultaneously and/or subsequently, preferably by distillation, the purified lower alkyl esters of higher fatty acids or the purified higher fatty acids from the treated material and the purified higher fatty acids are then esterified with lower alkanols.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the preparation of lower alkyl 
esters of higher fatty acids having improved properties for processing 
into surface-active .alpha.-sulfo-fatty acid esters. 
The preparation of surface-active .alpha.-sulfo-fatty acid esters from fats 
and oils especially of natural origin, has been known for years. For 
example, U.S. Pat. No. 2,195,187 describes .alpha.-sulfo-fatty acids and 
their esters as surface-active compounds or surfactants. They are obtained 
by the sulfonation of lower alkyl esters of saturated higher fatty acids 
with sulfur trioxide. The lower alkyl esters of higher fatty acids are 
obtained by reesterification of hydrogenated fats or oils with monovalent, 
lower alkanols, especially methanol, or by the cleavage of glycerides and 
subsequent esterification of the fatty acids. 
Henkel KGaA has been concerned intensively with this class of 
surface-active .alpha.-sulfonated fatty acids and respective fatty acid 
esters as well as their salts. The German Published Application DE-AS No. 
12 46 718, for example, describes a process for the preparation of this 
class of compounds. Fatty acids and fatty acid esters that have 6 to 28 
carbon atoms in the fatty acid radical, have no other groups that can be 
sulfonated or sulfated beside the carbon atom in .alpha.-position, and 
have an iodine number of less than 5, are sulfonated with a mixture of 
sulfur trioxide and inert gas, and the reaction product is neutralized. A 
parallel procedure working with the same substances is described in DE-AS 
No. 12 48 645. 
One of the main problems of the area involved here is the color instability 
of the lower alkyl esters of higher fatty acids in the sulfonation step. 
The crude products obtained are dark colored, brown-black and must be 
processed into light-colored products for use in washing and cleaning 
agent compositions. While the color of the crude sulfonation products does 
depend to some degree on the working conditions, the technical utilization 
of these, of themselves interesting possible starting materials, still is 
hampered by the following principle: The higher the yield of the reaction 
in the sulfonation step (the degree of sulfonation), the darker the color 
of the reaction product and the greater the problems to obtain 
light-colored end products. 
The significance of the constitution of the fatty acids or the fatty acid 
mixtures to be sulfonated is considered as certain knowledge by the 
experts in the field. Especially the stipulation is made that the fatty 
acids to be sulfonated in the .alpha.-position shall not have any double 
bonds, or as few as possible, nor any other types of reactive groups, 
especially hydroxyl groups. With the selection of suitable fats or oils, 
this problem is limited to the removal of unsaturated bonds in the fatty 
acid molecule. These sources of interference are eliminated by 
hydrogenating the starting material as completely as possible before the 
sulfonation. The literature of the state of the art indicates required 
iodine numbers of less than 5, preferably less than 2. Much lower iodine 
numbers, that is, those in the range from 0.1 to 0.3, are used in the 
practical examples. 
The removal of interfering accompanying substances by distillation or other 
methods from the fatty acids or fatty acid mixtures to be sulfonated is 
called for to reduce the discoloration problem, for example in DE-AS No. 
12 48 645. 
However, bleaching of the crude sulfonic acid derivatives always is 
necessary as final step in the process. The state of the art has evolved 
particularly two types of procedures for this purpose: Acid bleaching with 
hydrogen peroxide, as described in German Patent DE-PS No. 11 79 931, or 
combination bleaching in which the initial hydrogen peroxide bleaching is 
followed by the neutralization of the sulfonated and partially bleached 
material, after which a final bleaching step is conducted, again with 
hydrogen peroxide or, more advantageously, with hypochlorite, as described 
in DE-AS No. 12 34 709, for example. 
The problem of discoloration becomes particularly difficult when the 
sulfonation is to be increased to yields exceeding 90%, or even to degrees 
of sulfonation above 95%. The teachings of the DE-OS No. 14 43 995 concern 
themselves with the problems arising from this. According to information 
in this published patent specification, sulfur trioxide has a strongly 
decomposing effect on saturated fatty acid esters free of alcoholic 
hydroxyl groups, and this results unavoidably in very dark, discolored 
sulfonation products in the preparation of highly sulfonated products with 
a degree of sulfonation of at least 90%, preferably 94%, and especially at 
least 96%. 
DE-OS No. 14 43 995 recommends the addition of water to the sulfonation or 
the sulfonation product in order to keep the discoloration within limits. 
But this method generates new problems for the practical application in 
addition to observing certain temperatures. The viscosity of the 
sulfonated starting product in the strongly acid range is seriously 
affected by smallest amounts of water. Even the addition of 2% hydrogen 
peroxide in the form of a 35% solution causes a steep rise in viscosity 
with sulfonation products having a chain length of C.sub.16 /C.sub.18. The 
danger of clogged lines can happen in the continuous technical-scale 
process. 
According to the available experience, the various difficulties developing 
in different steps of the entire process force a compromise between the 
degree of sulfonation and bleaching. The optimal degree of sulfonation 
obtainable in practice are close to approximately 90%. 
It is common knowledge that natural starting materials such as plant and/or 
animal fats or oils generally are subject to certain variations in 
quality, due, for example, to the peculiarities of their origin and/or 
their handling up to the planned further processing. These variations 
bring with them a certain increase in problems in further processing, in 
contrast to standardized, purely synthetic starting materials. 
Consequently, there exists in the respectively more circumscribed field of 
the lower alkyl esters of higher fatty acids, a need for the 
standardization of the product quality of different starting materials by 
a simple refining procedure as well as for improvement of the processing 
characteristics of the refined materials, which guarantees dependable and 
improved subsequent processing results and/or products with improved 
characteristics in the large-scale operation. 
OBJECTS OF THE INVENTION 
An object of the present invention is the development of a process for the 
preparation of lower alkyl esters of higher fatty acids with improved 
processing properties by a simple refining procedure. 
Another object of the present invention is the development of a process for 
the preparation of lower alkyl esters of higher fatty acids with improved 
processing properties comprising the steps selected from the group 
consisting of 
(A) subjecting lower alkyl esters of higher fatty acids of plant and/or 
animal origin, to a heat treatment above 150.degree. C., in the presence 
of an effective amount to reduce the hydroxyl number of a material 
selected from the group consisting of esterification catalysts and 
carboxylic acid anhydrides, for a time sufficient to effect an improvement 
in further processing properties, separating purified lower alkyl esters 
of higher fatty acids from the treated material and recovering said lower 
alkyl esters of higher fatty acids with improved processing properties, 
and 
(B) subjecting free higher fatty acids of plant and/or animal origin to a 
heat treatment in the presence of an effective amount to reduce the 
hydroxyl number of a material selected from the group consisting of 
esterification catalysts and carboxylic acid anhydrides, for a time 
sufficient to effect an improvement in further processing properties, 
separating purified higher fatty acids from the treated material, 
esterifying the purified higher fatty acids with a lower alkanol under 
esterification conditions, and recovering said lower alkyl esters of 
higher fatty acids with improved processing properties. 
These and other objects of the present invention will become more apparent 
as the description thereof proceeds. 
The invention is based on the objective of the requirement of obtaining a 
uniform starting material for further processing, particularly by 
sulfonation, which product has improved processing properties. With it, 
the described problems of discoloration of alkyl esters of fatty acids or 
their mixtures during sulfonation are to be reduced, for example. The 
invention is an attempt to create, in a limited sense, a pretreatment for 
the alkyl esters of fatty acids to be sulfonated, which makes an effective 
curtailment of the discoloration in the subsequent sulfonation step 
possible. On the other hand, the invention is an attempt at the 
standardization of the fatty acids or alkyl esters of fatty acids from 
natural sources, by a simple refining procedure, to permit reproducible 
processing results, for example, during the sulfonation of the alkyl 
esters of fatty acids. In particular, the invention is also an attempt to 
adapt starting materials of lower quality to the subsequent purification 
steps into high-quality materials. 
The technical solution of the objects of the invention is based on the 
discovery that the desired goal is achieved if the alkyl esters of fatty 
acids are subjected to a thermal pretreatment under specific conditions 
given below, or if the free fatty acids are subjected to this pretreatment 
and are subsequently esterified with the corresponding alcohols. 
Thus, the subject of the invention is a process for the preparation of 
lower alkyl esters of higher fatty acids with improved processing 
properties from higher fatty acids of plant and/or animal origin. The 
process according to the invention is characterized by the fact 
(A) that the starting material containing the lower alkyl esters of higher 
fatty acids is subjected to a relatively brief temperature treatment above 
150.degree. C. in the presence of esterification catalysts and/or 
carboxylic acid anhydrides, and the so-reacted lower alkyl esters of 
higher fatty acids are separated from the added adjuvants and small 
amounts of high-boiling substances formed during the treatment, preferably 
by distillation, or 
(B) that the starting material containing free higher fatty acids is 
subjected to a relatively brief temperature treatment in the presence of 
esterification catalysts and/or carboxylic acid anhydrides, the so-treated 
higher fatty acids are separated from the added adjuvants and small 
amounts of high boiling substances formed during the treatment, preferably 
by distillation, and the purified free higher fatty acids are esterified 
by lower alkanols in a conventional manner. 
More particularly, the present invention relates to a process for the 
preparation of lower alkyl esters of higher fatty acids with improved 
processing properties comprising the steps selected from the group 
consisting of 
(A) subjecting lower alkyl esters of higher fatty acids of plant and/or 
animal origin, to a heat treatment above 150.degree. C., in the presence 
of an effective amount to reduce the hydroxyl number of a material 
selected from the group consisting of esterification catalysts and 
carboxylic acid anhydrides, for a time sufficient to effect an improvement 
in further processing properties, separating purified lower alkyl esters 
of higher fatty acids from the treated material and recovering said lower 
alkyl esters of higher fatty acids with improved processing properties, 
and 
(B) subjecting free higher fatty acids of plant and/or animal origin to a 
heat treatment above 150.degree. C. in the presence of an effective amount 
to reduce the hydroxyl number of a material selected from the group 
consisting of esterification catalysts and carboxylic acid anhydrides, for 
a time sufficient to effect an improvement in further processing 
properties, separating purified higher fatty acids from the treated 
material, esterifying the purified higher fatty acids with a lower alkanol 
under esterification conditions, and recovering said lower alkyl esters of 
higher fatty acids with improved processing properties. 
This temperature pretreatment is performed preferably in the range up to 
approximately 280.degree. C. and especially in the temperature range from 
about 200.degree. to 250.degree. C. Temperatures in the range from 
200.degree. to about 230.degree. C. can be especially advantageous. The 
treatment conditions and especially the treatment temperature and the time 
the starting material to be purified remains at this temperature under the 
process conditions are mutually adjusted, preferably in the manner to be 
described in the following. 
The duration of the pretreatment according to the invention, that is, the 
time the alkyl esters of the fatty acid or the free fatty acid starting 
material remains under the treatment conditions, is generally relatively 
brief. It may last for up to 15 minutes, for example, but considerably 
shorter times can be used in preferred practical examples of the 
invention. If needed, the thermal pretreatment according to the invention 
can be extended, for example, up to 30 minutes or also to about one hour. 
However, no significant processing advantages are generally connected with 
this extension. 
In the preferred practical example of the invention, the conditions of the 
refining step according to the invention, and here especially the 
treatment temperature and the time the material is treated, are mutually 
adjusted so that an esterification or reesterification of free hydroxyl 
groups can take place, preferably without any other substantial alteration 
in the structure of the alkyl esters of the fatty acid or the free fatty 
acid. This measure according to the invention becomes comprehensible with 
the following explanation. The alkyl ester of the fatty acid or the free 
fatty acid starting material apparently contains interfering components, 
which are present in varying quantities depending on origin and individual 
history of the respective alkyl ester of the fatty acid or free fatty acid 
material. These interfering components obviously are compounds that are 
hydroxylated on the chain, which may be present only in trace quantities 
but make themselves known by a disproportionate interference during the 
subsequent processing, possibly after esterification, of the alkyl esters 
of the fatty acids. With the temperature pretreatment under the given 
conditions, the process according to the invention is designed to create 
the possibility of obtaining a standardized, purified alkyl ester of a 
fatty acid product that does no longer have the described disadvantages in 
the subsequent processing phases. The pretreatment according to the 
invention actually allows the separation of smallest quantities of 
interfering accompanying substances from the fatty acid esters or free 
fatty acids that are not hydroxylated on the chain by a simple reaction. 
The esterification or reesterification of the components containing free 
hydroxyl groups with the ester or carboxyl groupings of the reaction 
materials present in an excess and/or the reaction with the added 
carboxylic acid anhydrides brings about such a shift in the boiling point 
of these interfering admixtures that the separation of the purified main 
part of the fatty acid esters or free fatty acid starting materials used 
from the formed high-boiling substances by distillation becomes possible. 
Alkyl esters of fatty acids or free fatty acids of natural origin usually 
are mixtures of varying amounts of saturated and unsaturated compounds, as 
they were obtained from the respective fats or oils of natural origin. 
Because of their individual histories of preparation and storing, mixing 
or blending and additional influences of this type, starting materials 
with widely varying qualifications must be expected in practice. The 
conversion of any different starting materials, by one constant method, 
into a product that can be processed more readily in one of the described 
following processing phases and/or will lead to improved end products, is 
possible with the pretreatment according to the invention. 
The reactive purification according to the invention can be facilitated by 
working under reduced pressure. Such a reduction in pressure should 
accelerate the shift in the equilibrium during the reesterification 
reaction between hydroxyl groups on the chains and the terminally located 
ester or carboxyl groupings, with the cleavage and removal of the 
monofunctional alcohol if the alkyl ester of fatty acid is used. In a 
preferred practical example, the work proceeds at such a reduced pressure 
that the distillation of the lower alkyl esters of fatty acids or the free 
fatty acids freed of interfering components becomes possible either 
simultaneously with or immediately following, the refining treatment 
according to the invention. For example, working with pressures in the 
range from 0.05 to 10 torr, particularly in the range from about 0.1 to 5 
torr, can be especially advantageous. The combining of the temperature 
pretreatment according to the invention for the reactive elimination of 
the interfering components and the separation by distillation of the 
purified material into a preferably continuously operating phase of the 
process is possible in this manner. The reactive conversion of the 
interfering accompanying components into high-boiling substances is 
accomplished in surprisingly short time spans that may be in the range of 
seconds or even fractions of a second. For example, it is possible 
according to the invention to add esterification catalysts and/or 
carboxylic acid anhydrides to the starting material to be purified and to 
distill the mixture, while maintaining the pot temperature of the material 
to be distilled above 150.degree. C. and preferably within the temperature 
range particularly suitable according to the invention. Thermal 
pretreatment and separation of the undesirable parts of the product thus 
are practically combined into one step of the process. Another especially 
technically simple modification provides that the esterification catalysts 
and/or carboxylic acid anhydrides, dissolved, for example, in a 
high-boiling substance, are charged in the temperature range of the 
pretreatment according to the invention and under reduced pressure. The 
starting material to be purified is fed into this reaction zone either 
proportionately or preferably continuously. Pressure and temperature 
conditions are mutually adjusted to guarantee the distillation of the 
major part of the fatty acid ester or free fatty acid material. Despite 
the very fast vaporization of the starting material fed into the reaction 
zone, the interfering components are converted by reaction at such a rate 
that the collected distillate has the desired improved processing 
properties. 
Especially in these latter practical examples of the simultaneous reactive 
purification and distillation, the work may proceed with holding times at 
the desired temperature in the range from about 0.1 to 3 minutes, for 
example, with temperatures preferably in the range from about 200.degree. 
to 250.degree. C. 
Esterification catalysts and/or carboxylic acid anhydrides are used as 
active additives in the process according to the invention. Any 
esterification catalysts from the extensive present state of the art may 
be used for this purpose. However, the work is performed preferably with 
basic, neutral or at most weakly acid catalysts or catalytic systems. 
Especially preferred is to conduct the work with catalysts that are 
soluble in the starting material to be purified and/or in high-boiling 
substances, which are formed during the process according to the invention 
and/or are used in the purification according to the invention in the 
sense described above. The use of liquid, soluble catalysts or catalytic 
systems can be particularly expedient. 
The compilation in J. Am. Oil Chem. Soc. 55: 796-805, 1978, especially the 
compilation from Table I on page 797, is cited simply as an example from 
the extensive state of the art concerning the esterification catalysts. 
Listed are metal salts such as acetates, carbonates, chlorides, nitrates 
and oxides of tin, zinc, iron, cobalt and lead; alkali metal hydroxides 
such as NaOH, KOH, LiOH; metal soaps such as the stearates of alkali 
metals, zinc, aluminum and titanium; alkali metals or their alloys; metal 
alkylates and metal hydrides. Especially suitable are metal soaps of 
saturated and/or unsaturated monocarboxylic or polycarboxylic acids with 
the carbon chain lengths C.sub.2 -C.sub.36 of the following metals: K, Na, 
Li, Al, B, Zn, Sn, Ca, Mg, Ti and V; metallic alcoholates of saturated and 
unsaturated monohydric or polyhydric linear or branched alcohols with the 
carbon chain length C.sub.1 -C.sub.36 with the following metals as cation: 
Li, Na, K, Mg, Ca, B, Al, Zn, Sn and Ti; the metal hydrides, that is, 
hydrogen compounds of the elements Li, Na, Mg, Ca, B, Al and Sn or their 
mixtures; and the metal alkyls, that is, carbon compounds of the elements 
Li, Na, Mg, Ca, B, Al, Sn and Ti, or their mixtures. 
An especially suitable class of catalysts or active additives is derived 
from soluble organic compounds of boric acid. Suitable are especially 
boric acid esters, for example, boric acid alkyl esters, among which those 
with relatively higher alcohols (C.sub.10 -C.sub.22, especially C.sub.12 
-C.sub.18 -alkanols) can be particularly preferred. But suitable are 
especially also esters of boric acid with partial esters of polyhydric 
alcohols, for example, the respective esters of polyhydric alcohols with 
mono- or diglycerides. These partial esters of polyhydric alcohols may 
also be derived from higher fatty alcohols, especially those in the carbon 
atom range of from 10 to 22. Boric acid esters that are liquid and/or 
soluble at the process temperature are a preferred catalyst class. 
Additional examples of suitable boric acid compounds are boric acid 
anhydride, sodium borate and sodium boronate. 
Carboxylic acid anhydrides can be used as active additives in addition to, 
or instead of, esterification catalysts in the temperature treatment 
according to the invention. However, the concurrent use of esterification 
catalysts that facilitate the reaction of the carboxylic acid anhydride 
with hydroxyl groups is preferred. The carboxylic acid anhydrides can be 
derived basically from monocarboxylic acids or polycarboxylic acids, 
especially from dicarboxylic acids in this case. In one practical example 
of the invention, the use of relatively high-boiling carboxylic acid 
anhydrides with a boiling point especially higher than that of the fatty 
acid esters or free fatty acids to be refined, is to be preferred. For 
example, carboxylic acid anhydrides boiling above 300.degree. C./l torr 
can be suitable starting materials for the process of the invention. Such 
carboxylic acid anhydrides are derived, for example, from C.sub.8 
-C.sub.28 -monocarboxylic acids, especially from monocarboxylic acids with 
10 to 22 carbon atoms (C.sub.10-22 -fatty acids). Working with such 
high-boiling carboxylic acid anhydrides facilitates the process according 
to the invention inasmuch as possibly present excesses of this active 
additive can be readily removed from the refined fatty acid ester or free 
fatty acid by a subsequent distillation. 
Also included under the term carboxylic acid anhydrides according to the 
invention are mixed acid anhydrides of carboxylic acids and inorganic 
acids, especially mixed acid anhydrides of higher fatty acids and boric 
acid. As explained, the fluidity of the reaction components used as 
additives may be desirable for the performance of the process according to 
the invention in a continuous operation. Distillation residues from the 
known treatment of fatty acids, for example, those of natural origin, with 
boric acid compounds that contain a not inconsiderable proportion of fatty 
acid anhydrides, mixed boric acid/fatty acid anhydrides and/or boric acid, 
are a suitable additive for the refining process according to the 
invention. These fluid distillation residues thus can be used in an 
important, further process step. 
The mentioned active additives (esterification catalysts and/or carboxylic 
acid anhydrides) usually are added only in small quantities to the fatty 
acid ester or free fatty acid starting material to be purified, although 
larger amounts are generally not harmful. Suitable are, for example, 
amounts from 0.01 to 20% by weight, especially amounts in the range from 
about 0.1 to to 10% by weight, of the active additive or additive mixture, 
calculated with respect to the fatty acid ester or free fatty acid 
starting material. Amounts of the active additive not exceeding 5% by 
weight, preferably not exceeding 3% by weight, will generally be used. The 
especially preferred range for the amount to be used lies between 0.05 and 
1.0% by weight. All of these percentages by weight are based on the fatty 
acid ester or free fatty acid starting material to be treated. When 
carboxylic acid anhydrides are used together with esterification 
catalysts, the catalysts may be used in the usual small amounts, for 
example, their amount is from 0.001 to 10% by weight, especially from 0.01 
to 5% by weight, calculated on the carboxylic acid anhydride. When the 
above described continuous process is used, in which the starting material 
to be purified is added to a reaction zone containing the esterification 
catalysts and/or carboxylic acid anhydrides, and purified fatty acid ester 
or free fatty acid material is simultaneously removed from this reaction 
zone by distillation, the only thing to be observed is the use of 
reesterification catalyst and/or carboxylic acid anhydride in an amount 
that is adequate to bring about the desired reactive removal of the 
interfering components within the brief time span available for the 
reaction. 
The purification of the lower alkyl esters of higher fatty acids according 
to the invention does not necessarily result in an improvement in color 
nor in a substantial change in the parameters (hydroxyl number, iodine 
number, saponification number and/or acid number). The effect of the 
pretreatment according to the invention does not manifest itself in the 
purified lower alkyl esters of higher fatty acids but only with its 
continued processing, that is, after the sulfonation of a starting 
material pretreated by this method. In this case, it is expressed in the 
better bleaching qualities of the sulfonation product, for example. 
Bleached products with Klett color numbers of less than 60 can be prepared 
without any problems. 
The pretreatment according to the invention can be carried out with fatty 
acid ester or free fatty acid fractions hardened by hydrogenation or still 
unhardened. When unhydrogenated material is treated, the obtained product 
fraction should be hardened as soon as possible to eliminate undesirable 
oxidative influences due to ageing via the double bonds in the product. 
A conventional separation of interfering components, presumably of the 
portions formed by oxidative ageing causing the hydroxylated methyl ester 
of fatty acids where the hydroxyls are located on the chain, from the 
problem-free parts of the starting material is practically impossible. A 
distillation does not achieve the objective. The teachings of the 
invention, that is, subjecting the starting material of any composition 
together with the active additives to the thermal pretreatment and 
especially distilling above this material, removes the existing 
difficulties and yields reliably a starting material suitable for the 
following sulfonation and bleaching. 
The knowledge of the state of the art applies to the subsequent sulfonation 
and bleaching. Details for the performance of the acid bleaching or 
multiphase combination bleaching are found, for example, in the German 
patents DE-PS Nos. 11 79 931 and 12 34 709 and the DE-OS No. 14 43 995. 
The described sulfonation is usually carried out at temperatures from 
70.degree. to 130.degree. C. in a descending film reactor with a mixture 
of gaseous sulfur trioxide and an inert gas, during a period of 10 to 20 
minutes and to give sulfonation degrees exceeding 90% especially exceeding 
92% and, as a rule, exceeding 94%. Sulfonation degrees of 95% and higher 
are especially preferred. Yet, sulfonation products with Klett numbers of 
50 or less can be prepared reliably with the use of the purification 
treatment according to the invention. 
Suitable higher fatty acid ester starting materials are especially the 
respective lower alkyl esters with preferably 1 to 5 carbon atoms in the 
alkanol radical. Especially important are the methyl esters of higher 
fatty acids that were obtained from plant and/or animal fats by 
reesterification or by saponification with subsequent esterification.

EXAMPLES 
The following examples explain the pretreatment according to the invention 
and its results along with comparison experiments that lie outside the 
scope of the invention. These examples are not to be deemed limitative in 
any respect. 
The purification effect of the process according to the invention is judged 
by the beachability of the ester sulfonate pastes obtained after 
sulfonation. 
The method of sulfonation and bleaching described below applies to all 
examples: 
Batches of 576 gm of a methyl ester of tallow fatty acids were sulfonated 
in a standing cylinder heated to 80.degree. C. by blowing in, over a 
period of 65 minutes, a 5% by volume mixture of SO.sub.3 in air, in such a 
rate that the total amount contained 208 gm(.apprch.2.6 mol) of SO.sub.3, 
and a subsequent after-reaction period of 15 minutes. The crude sulfonic 
acid obtained was neutralized by the simultaneous addition of crude 
sulfonic acid and sodium hydroxide solution together to give a mixture in 
the pH range from 6.5 to 8 to form a aqueous paste containing about 25% 
sulfonation product. This sulfonation product was then bleached at 
60.degree. C. with 15.4% by weight, based on the sulfonation product, of a 
13% aqueous NaOCl solution. A 5% aqueous solution of the sulfonation 
product, adjusted to pH 7, had a Klett number as mentioned in the 
individual examples, when it was measured with the blue filter (420 mm) in 
a Klett round-glass cell on the Klett-photometer (Model 800- 3 by 
Klett-Summerson). The degree of sulfonation of the pastes obtained was 
between 95 and 97%. 
COMISON EXAMPLE A 
The starting material was a methyl ester of a hardened (hydrogenated) 
tallow fatty acid, obtained by splitting of tallow, washing out the 
glycerol, esterification of the tallow fatty acid with methanol, then 
hardening (hydrogenation of the existing C-C double bonds) and 
distillation. This methyl ester of a hardened tallow fatty acid had the 
following values: iodine number 0.3; hydroxyl number 2.0; acid number 0.6; 
saponification number 194.4, and was sulfonated as described above, 
neutralized, and bleached. After a bleaching time of 30 minutes, the Klett 
number of the ester sulfonate paste was 255. 
EXAMPLE 1 
The hardened methyl ester of tallow fatty acid used in Comparison Example A 
was distilled before sulfonation by mixing with 0.5% by weight, based on 
the methyl ester of the fatty acid, of lithium aluminum hydride, and by 
heating to a sump temperature of 230.degree. C./0.1 mbar. The distillation 
residue minus the lithium aluminum hydride was 8.5% by weight. The methyl 
ester of the hardened tallow fatty acid thus purified had the following 
values: iodine number 0.; hydroxyl number 0; acid number 0.2; 
saponification number 194.3; and was sulfonated under the above stated 
conditions, neutralized and bleached. After a bleaching time of 30 
minutes, the Klett number of the ester sulfonate paste was 42. 
EXAMPLE 2 
The hardened methyl ester of tallow fatty acid used in Comparison Example A 
was distilled before the sulfonation in the presence of 0.5% by weight, 
based on the methyl ester of the fatty acid, of aluminum chloride, and by 
heating to a sump temperature of 230.degree. C./0.1 mbar. The distillation 
residue minus the aluminum chloride was 2.8% by weight. The purified 
hardened methyl ester of tallow fatty acid had the following values: 
iodine number 0.2; hydroxyl number 0; acid number 0.2; saponification 
number 193.8; and was sulfonated as described above, neutralized, and 
bleached. After a bleaching time of 30 minutes, the Klett number of the 
ester sulfonate paste was 50. 
EXAMPLE 3 
The hardened methyl ester of tallow fatty acid used in Comparison Example A 
was distilled before the sulfonation with an addition of 0.5% by weight, 
based on the methyl ester of the fatty acid, of sodium-aluminum 
hydridotrimethylate NaAlH(OCH.sub.3).sub.3 ; and by heating to a sump 
temperature of 230.degree. C./0.1 mbar. The distillation residue minus the 
catalyst was 2.4% by weight. The purified hardened methyl ester of tallow 
fatty acid had the following values: iodine number 0.2; hydroxyl number 0; 
acid number 0.3; saponification number 194.2; and was sulfonated as 
described above, neutralized, and bleached. After a bleaching time of 30 
minutes, the Klett number of the ester sulfonate paste was 45. 
COMISON EXAMPLE B 
The starting material was a methyl ester of a hardened (hydrogenated) 
tallow fatty acid which had been obtained by splitting of tallow, washing 
out the glycerol, esterification of the tallow fatty acid with methanol, 
hydrogenation of the existing C-C double bonds, and distillation. This 
methyl ester of hardened tallow fatty acid had the following values: 
iodine number 0.2; hydroxyl number 1.8; acid number 0.2; saponification 
number 194.4; and was sulfonated as described above, neutralized, and 
bleached. After a bleaching time of 2 hours, the Klett number was 200. 
EXAMPLE 4 
The methyl ester of the hardened tallow fatty acid used as starting 
material in Comparison Example B was distilled before the sulfonation in 
the presence of 5% by weight, based on the methyl ester of fatty acid, of 
boric acid by heating to a sump temperature of 230.degree. C./0.1 mbar. 
The distillation residue minus the boric acid present was 0.8% by weight. 
This methyl ester of tallow fatty acid was sulfonated in the stated 
manner, neutralized, and bleached. After a bleaching time of 2 hours, the 
Klett number was 33. 
COMISON EXAMPLE C 
A methyl ester of a hardened tallow fatty acid, obtained as in Comparison 
Example A, with the values: iodine number 0.3; hydroxyl number 2.0; acid 
number 0.6; saponification number 194.4, was sulfonated as described 
before, neutralized, and bleached. After a bleaching time of 4 hours, the 
Klett number of the ester sulfonate paste was 200. 
EXAMPLE 5 
The methyl ester of the hardened tallow fatty acid used in Comparison 
Example C was distilled before the sulfonation in the presence of 2% by 
weight, based on the methyl ester of the fatty acid, of aluminum stearate 
by heating to a sump temperature of 230.degree. C./0.1 mbar. The 
distillation residue minus the aluminum stearate present was 3.5% by 
weight. The purified methyl ester of hardened tallow fatty acid having an 
iodine number 0.3; hydroxyl number 0; acid number 0.8; saponification 
number 194.1, was sulfonated as stated above, neutralized, and bleached. 
After a bleaching time of 4 hours, the Klett number of the ester sulfonate 
paste was 50. 
EXAMPLE 6 
The hardened methyl ester of tallow fatty acid used in Comparison Example C 
was distilled before the sulfonation with the addition of 1% by weight, 
based on the methyl ester of the fatty acid, of iron (III) chloride by 
heating to a sump temperature of 230.degree. C./0.1 mbar. The distillation 
residue, minus the iron (III) chloride present, was 4.5% by weight. The 
thus purified methyl ester of hardened tallow fatty acid with an iodine 
number 0.6; hydroxyl number &lt;1; acid number 0.2; saponification number 
194.0 was sulfonated as described above, neutralized, and bleached. After 
a bleaching time of 4 hours, the Klett number of the ester sulfonate paste 
was 80. 
COMISON EXAMPLE D 
The starting material was a methyl ester of a hardened tallow fatty acid, 
obtained by transesterification of tallow with methanol with subsequent 
distillation and hardening (hydrogenation of existing C-C double bonds). 
The ester obtained had the values: iodine number 0.55; hydroxyl number &lt;1; 
acid number 0.4; saponification number 194.0. This ester was sulfonated, 
neutralized, and bleached. After a bleaching time of 30 minutes, the Klett 
number of the ester sulfonate paste obtained was 260. 
COMISON EXAMPLE E 
The methyl ester of tallow fatty acid used in Comparison Example D with the 
iodine number 0.55 was further hardened to an iodine number of 0.1. This 
ester was sulfonated as described, neutralized, and bleached. After a 
bleaching time of 30 minutes, the Klett number of the ester sulfonate 
paste was 180. 
EXAMPLE 7 
The rehardened methyl ester of tallow fatty acid used in Comparison Example 
E was distilled before the sulfonation with addition of 0.5% by weight, 
based on the methyl ester of the fatty acid, of sodium-boron hydride by 
heating to a sump temperature of 230.degree. C./0.1 mbar. The distillation 
residue was 2.8% by weight. The thus purified methyl ester of tallow fatty 
acid was sulfonated as described above, neutralized, and bleached. After a 
bleaching time of 30 minutes, the Klett number of the ester sulfonate 
paste obtained was 40. 
EXAMPLE 8 
To prepare the catalyst, 379 gm of tallow fatty acid and 7.5 gm of boric 
acid were stirred for 3 hours at 200.degree. C. Then the mixture obtained 
was distilled by heating to a sump temperature of 280.degree. C./0.1 mbar. 
There were obtained 82 gm of a residue having a melting point of about 
60.degree. C. 
The starting material used in Comparison Example E was distilled before the 
sulfonation in the presence of 1.5% by weight, based on the methyl ester 
of tallow fatty acid charged, of the catalyst by heating to a sump 
temperature of 230.degree. C./0.1 mbar. The distillation residue was 3% by 
weight. The distilled hardened methyl ester of tallow fatty acid was 
sulfonated in the manner described, neutralized, and bleached. After a 
bleaching time of 30 minutes, the Klett number of the ester sulfonate 
paste obtained was 27. 
COMISON EXAMPLE F 
The starting material was a hardened methyl ester of tallow fatty acid, 
obtained by transesterification of tallow with methanol with subsequent 
distillation and hardening. This material was subjected to a second 
distillation. The obtained hardened methyl ester of tallow fatty acid was 
free from glycerides and had the following values: iodine number 0.25; 
hydroxyl number 1.0; acid number 0.2; saponification number 196.4. This 
ester was sulfonated in the described manner, neutralized, and bleached. 
After a bleaching time of 2 hours, the Klett number of the ester sulfonate 
paste obtained was 95. 
EXAMPLE 9 
For the preparation of the catalyst, 500 gm of tallow fatty acid and 2.5 gm 
of boric acid were stirred for one hour at 200.degree. C./133 mbar, and 
the mixture was then distilled by heating to a sump temperature of 
280.degree. C./0.1 mbar. The residue was 120 gm. 
The starting material used in Comparison Examle F was distilled before the 
sulfonation with addition of 1.3% by weight, based on the methyl ester of 
fatty acid, of the previously prepared catalyst, by heating to a sump 
temperature of 230.degree. C./0.1 mbar. The distillation residue was 1.6% 
by weight. The purified methyl ester of tallow fatty acid was sulfonated 
as described above, neutralized, and bleached. After a bleaching time of 2 
hours, the Klett number of the ester sulfonate paste obtained was 30. 
COMISON EXAMPLE G 
The starting material was a methyl ester of a tallow fatty acid, obtained 
by transesterification of tallow with methanol followed by distillation 
and hardening. The hardened material was subjected to a second 
distillation. The obtained methyl ester of tallow fatty acid was free from 
glycerides and had the values: iodine number 0.2; hydroxyl number 0.8; 
acid number 0.6; saponification number 196.6. This hardened methyl ester 
of tallow fatty acid was sulfonated as described, neutralized, and 
bleached. After a bleaching time of 30 minutes, the Klett number of the 
obtained ester sulfate paste was 135. 
EXAMPLE 10 
For the preparation of the catalyst, 320 gm of a mixture of 45% by weight 
of glycerol monostearate, 41% by weight of glycerol distearate, and 14% by 
weight of glycerol tristearate were stirred together with 62 gm of boric 
acid for 3 hours at 160.degree. C./66.5 mbar. The boric acid dissolved. 
The reaction product had a melting point of about 50.degree. C. 
The starting material used in Comparison Example G was distilled before the 
sulfonation in the presence of 0.9% by weight, based on the fatty acid 
ester charged, of the previously prepared catalyst, by heating to a sump 
temperature of 230.degree. C./0.1 mbar. The distillation residue was 1.7% 
by weight. The distilled hardened methyl ester of tallow fatty acid was 
sulfonated in the manner described, neutralized, and bleached. After a 
bleaching time of 30 minutes, the Klett number of the ester sulfonate 
paste obtained was 46. 
EXAMPLE 11 
The starting material used in Comparison Example F was distilled before the 
sulfonation in the presence of 1.0% by weight, based on the methyl ester 
of fatty acid, of zinc stearate, by heating to a sump temperature of 
230.degree. C./0.1 mbar. The distillation residue was 2.0% by weight. The 
distilled hardened methyl ester of tallow fatty acid was sulfonated as 
described, neutralized, and bleached. After a bleaching time of 2 hours, 
the Klett number of the ester sulfonate paste obtained was 47. 
EXAMPLE 12 
The starting material used in Comparison Example G was distilled before the 
sulfonation with an addition of 0.5% by weight, based on the methyl ester 
of fatty acid, of sodium methylate, by heating to a sump temperature of 
230.degree. C./0.1 mbar. The distillation residue was 6.3% by weight. The 
purified methyl ester of tallow fatty acid was sulfonated as described, 
neutralized, and bleached. After a bleaching time of 30 minutes, the Klett 
number of the ester sulfonate paste was 40. 
EXAMPLE 13 
For the preparation of the catalyst, 379 gm of hardened tallow fatty acid 
(iodine number 0.3) and 7.5 gm of boric acid were stirred for 3 hours at 
200.degree. C., and the mixture was subsequently distilled by heating to a 
sump temperature of 280.degree. C./0.1 mbar. There were obtained 82 gm of 
a residue having a melting point of about 60.degree. C. 
In the starting material used in Comparison Example E, 1.5% by weight, 
based on the methyl ester of fatty acid charged, of the catalyst were 
dissolved. This mixture was transferred continuously, drop by drop, into a 
distillation flask heated to 230.degree. C. at 0.1 mbar, the inflow having 
been regulated so that it matched the quantity distilling. The 
distillation residue was 2% by weight. The methyl ester of tallow fatty 
acid thus distilled was sulfonated as described before, neutralized, and 
bleached. After a bleaching time of 30 minutes, the Klett number of the 
ester sulfonate paste obtained was 50. 
EXAMPLE 14 
The starting material was an unhardened tallow fatty acid, obtained by 
splitting of tallow and washing out the glycerol. This tallow fatty acid 
was distilled in the presence of 1% by weight, based on the fatty acid 
charged, of sodium boron hydride, by heating to a sump temperature of 
230.degree. C./0,1 mbar. The distilled tallow fatty acid was heated with 
methanol in the weight ratio 1:1.1 in an autoclave for 2 hours at 
200.degree. C. Then unreacted methanol was removed by distillation. The 
residue was again admixed with 1.1 parts by weight of methanol to 1 part 
tallow fatty acid charged and again heated in the autoclave for 2 hours at 
200.degree. C. This operation was repeated once more after the 
distillation of the unreacted methanol from the reaction mixture. The 
methyl ester of tallow fatty acid then remaining after the distillation of 
the methanol was hydrogenated with the addition of 0.3% by weight of Raney 
nickel, based on the fatty acid ester charged, in an autoclave at 
200.degree.-220.degree. C. under a hydrogen pressure of 20 bar for a 
period of 2 hours. The hardened methyl ester of tallow fatty acid obtained 
after separation of the catalyst had the values: iodine number 0.1; 
hydroxyl number 0; acid number 5.9; saponification number 195.4. This 
ester was sulfonated in the described manner, neutralized, and bleached. 
After a bleaching time of 30 minutes, the Klett number of the ester 
sulfonate paste obtained was 42. 
EXAMPLE 15 
An unhardened tallow fatty acid, obtained by splitting of tallow and 
washing out of glycerol, was hydrogenated under the conditions stated in 
Example 14. The hardened tallow fatty acid was then distilled in the 
presence of 1% by weight, based on the charged acid, of sodium boron 
hydride, by heating to a sump temperature of 230.degree. C./0,1 mbar. The 
distilled tallow fatty acid was then esterified with methanol under the 
conditions stated in Example 14. The obtained hardened methyl ester of 
tallow fatty acid with the values: iodine number 0.5; hydroxyl number 0; 
acid number 5.5; saponification number 198 was sulfonated as described 
above, and bleached. After a bleaching time of 2 hours, the Klett number 
of the obtained ester sulfonate paste was 44. 
EXAMPLE 16 
An unhardened tallow fatty acid, obtained by splitting of tallow and 
washing out the glycerol, was distilled with addition of 1% by weight, 
based on the fatty acid charged, of the catalyst from Example 10, by 
heating to a sump temperature of 230.degree. C./0,1 mbar. The purified 
tallow fatty acid was esterified with methanol under the conditions stated 
in Example 14. The methyl ester obtained was hydrogenated under the 
conditions stated in Example 14. The hardened methyl ester of tallow fatty 
acid had the values: iodine number 0; hydroxyl number 0; acid number 5.4; 
saponification number 195.4, and was sulfonated in the stated manner, 
neutralized, and bleached. After a bleaching time of 30 minutes, the Klett 
number of the obtained ester sulfonate paste was 50. 
EXAMPLE 17 
An unhardened tallow fatty acid, obtained by splitting of tallow and 
washing out the glycerol, was hydrogenated under the conditions stated in 
Example 14. The hardened tallow fatty acid obtained was distilled with 
addition of 5% by weight, based on the fatty acid charged, of the catalyst 
from Example 10, by heating to a sump temperature of 230.degree. C./0,1 
mbar. The distilled acid was then esterified with methanol under the 
conditions stated in Example 14. The hardened methyl ester of tallow fatty 
acid obtained had the values: iodine number 0.4; hydroxyl number 0; acid 
number 2.7; saponification number 198, and was sulfonated as described 
above, neutralized, and bleached. After a bleaching time of 2 hours, the 
Klett number of the ester sulfonate paste obtained was 38. 
The preceding specific embodiments are illustrative of the practice of the 
invention. It is to be understood, however, that other expedients known to 
those skilled in the art or disclosed herein may be employed without 
departing from the spirit of the invention or the scope of the appended 
claims.