Process for the fractionation of wool wax acid mixtures

Disclosed is a process for the fractionation of wool wax acid mixtures by dissolving the starting material in a polar organic solvent (mixture). The dissolved wool wax acid mixture is treated at a temperature between -5 and 30.degree. C. and at a pressure between 10 and 70 bar with gaseous carbon dioxide and the hydroxy-fatty acids that accumulate as a solid are separated from the solution.

BACKGROUND OF THE INVENTION 
The present invention concerns a process for the fractionation of wool wax 
acid mixtures that enables the fraction of hydroxy-fatty acids to be 
separated from the fraction of non-hyroxylated fatty acids and thus 
enables the hydroxy-fatty acids to be obtained as a crystalline product 
and in high purity. 
A chemically nonhomogenous fraction of long chain carboxylic acids can be 
obtained from natural wool wax (lanolin) which are essentially composed of 
branched and unbranched fatty acids as well as hydroxy-fatty acids and 
above all alpha-hydroxy-fatty acids (Motiuk, K.; J. Am. Oil Soc. 56, 91 
(1979)). The interest in suitable processes to separate the complex 
mixture of acids has arisen since the cosmetic and pharmaceutical 
industries have discovered their different use in various fields of 
application. A particular advantage in this connection is the 
toxicological safety of wool wax and its components in particular for 
topical applications in cosmetic formulas (J. Environ. Path. Tox. 4, 63-92 
(1980)). 
In the corresponding literature numerous procedures are described which can 
be used to separate mixtures of wool wax acid. These processes are based 
on the techniques of distillation, crystallization or solvent extraction, 
but all of these processes have considerable disadvantages. In 
distillation processes there is a general tendency that the potential 
product is prone to undesired reactions by an excessive thermal stress 
such as e.g. lactide formation between two alpha hydroxy acid molecules or 
dehydration reactions which ultimately cause high losses in yield. 
In crystallization processes solvent mixtures have often been used for 
which relatively long crystallization procedures have to be employed 
providing poor space-time yields and consequently, less advantageous 
process economy. Additionally, these processes generally lead to an 
inadequate separation. Recently a new solvent process for the 
fractionation of wool wax acid mixtures was disclosed in EP 0 555 776 A1 
which recommends at least two extraction steps with organic solvents of 
different polarity in order to obtain a effective separation and adequate 
purity of the acid fractions. In order to achieve a high product purity 
the process cycle of crystallization may have to be repeated several times 
with an additional salting-out procedure. Apart from the long processing 
time, which is in the range of several hours, a major technological 
problem may occur when carrying out the process on a large scale: the 
undissolved fatty acid fractions are often wax-like and/or of highly 
viscous consistency and tend to block the filter system. The objective of 
that process, which is to obtain the hydroxy-fatty acids in a pure and 
crystalline form, can only be achieved in a very complicated manner and 
with technological problems. 
The object of the present invention is therefore to present a process for 
the fractionation of wool wax acid mixtures that circumvents the said 
disadvantages of the known processes in order to achieve a straightforward 
fractionation of the starting materials into hydroxylated and 
non-hydroxylated fatty acid fractions of high purity. 
THE INVENTION 
The above stated object is achieved according to the invention by 
dissolving the mixture of wool wax acids in a polar solvent (mixture), 
subjecting this solution to a pressure treatment with gaseous carbon 
dioxide at temperatures between -5 and 30.degree. C. and at a process 
pressure between 10 and 70 bar and precipitating by this way the 
hydroxy-fatty acids as a solid from the solution. Surprisingly it has been 
found that the expansion behaviour of the respective solvent can be 
specifically controlled by the pressure of the gaseous carbon dioxide 
effecting a selective precipitation of the hydroxy-fatty acids in 
crystalline form that can be recovered from the solution in a 
straightforward manner. 
According to the invention polar organic solvents with up to 5 C atoms from 
the series of short-chained esters such as in particular ethyl acetate, 
ketones such as in particular acetone and alcohols such as methanol and 
ethanol or mixtures of these solvents are used to dissolve the starting 
material. The mixture of wool wax acids to be fractionated is dissolved in 
these solvents preferably at a concentration between 10 and 50 % by 
weight, particularly preferably between 20 and 40 % by weight, and at room 
temperature i.e. preferable between 15 and 25.degree. C. for which only a 
few minutes are required. 
The fractionation procedure with this solution is subsequently carried out 
by subjecting the solvent (mixture) to a pressure of gaseous carbon 
dioxide at a temperature between -5 and 30.degree. C. over a certain 
period of time, between 5 and 60 minutes. The dissolution of the gas in 
the solvent (mixture) causes an expansion of the volume of the solvent 
thus effecting the precipitation of the hydroxy-fatty acid fraction. It is 
expedient to carry out the process in a temperature-controlled pressure 
vessel. The maximum process pressure at a given temperature is limited by 
the pressure at which the carbon dioxide gas begins to liquefy which, 
however, is not quite reached in the fractionation according to the 
present process. At the maximum process temperature of 30.degree. C. 
fractionating pressure attains its maximum value i.e. about 70 bar; at the 
minimum process temperature of -5.degree. C. the pressure is about 25 bar. 
After a period of 5 to 60 minutes at fractionation conditions (pressure 
and temperature) which completes the precipitation, the obtained sediment, 
mainly composed of the hydroxy-fatty acid mixture, is separated from the 
solution while maintaining the process conditions constant. According to a 
preferred embodiment this separation step is carried out in a technically 
advantageous manner by means of a filter plate at the bottom of the 
pressure vessel in front of the outlet as filtering device to recover the 
precipitate. The non-hydroxylated fatty acids which essentially remain in 
solution can be isolated from the filtrate after the separation step, 
preferably by removing the organic solvent (mixture) by evaporation, 
optionally under reduced pressure. 
The yield and purity of the precipitated hydroxy-fatty acids can be 
directed according to the invention by the process parameters, temperature 
and carbon dioxide pressure, and the selected solvent (mixture). Thus the 
separation of the mixture can be specifically controlled with these 
process parameters in accordance with the objective of the process. 
In a further preferred embodiment of the process according to the invention 
the hydroxy-fatty acids, which accumulate as a crystalline precipitate are 
washed with liquid carbon dioxide. The washing effects the removal of the 
solvent residues and undesired flavor compounds and considerably improves 
the quality of the product. For this purpose the carbon dioxide is used at 
subcritical temperatures of &lt;30.degree. C. and at pressures of &lt;100 bar 
i.e. in a liquid state. Due to the fact that the hydroxy-fatty acids have 
only a very low solubility in liquid carbon dioxide, the washing procedure 
can be performed without significant losses of product. The amount of 
liquid carbon dioxide for the washing step can be varied within a wide 
range depending on the degree of the desired improvement in quality. 
Advantageously, the amount for washing is selected between 0.5 and 100 g 
carbon dioxide per g hydroxy-fatty acid. 
This rewashing of the filter residue with liquid carbon dioxide enhances 
the purity of the hydroxy-fatty acids by removing solvent residues leading 
to a dry product and effecting at the same time the elimination of the 
undesired characteristic odor of the starting material. 
The significant advantages of the process according to the invention in 
comparison with the known processes are consequently that the 
hydroxy-fatty acids can be accumulated as a crystalline product which can 
be readily separated by filtration and that the process time can be kept 
comparatively short so that a good space/time yield can be achieved. 
Moreover, the process can be carried out under mild temperature conditions 
avoiding thermal damage to the products. 
The following examples are intended to elucidate these advantages of the 
process according to the invention.

EXAMPLES 
The process examples were carried out in a high pressure autoclave with an 
inspection glass and jacket cooling (autoclave volume 400 ml). A sintered 
metal plate is located at the bottom of the autoclave in front of an exit 
over which the sediment composed of hydroxy-fatty acids can be separated. 
The wool wax acid mixture (WWA) used has a hydroxy number of 60. 
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Example 1 2 3 
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Solvent Acetone Ethyl acetate 
Ethanol 
Solvent volume (ml) 
50 50 50 
WWA in solution (% by weight) 
25 25 25 
CO.sub.2 pressure (bar) 
30 28 30 
Temperature of the pressure 
0 -5 0 
treatment (.degree.C.) 
Time for sedimentation (min) 
45 45 30 
Relative sediment yield (% of 
21 17 18 
WWA) 
OH number of the filtrate residue 
190 182 210 
OH number of the eluate 
26 35 27 
Rehashing with CO.sub.2 
-- -- + 
Temperature (.degree.C.) 
-- -- 25 
Pressure (bar) -- -- 75 
Amount of CO.sub.2 for washing (g/g 
-- -- 3 
hydroxy-fatty acid mixture) 
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It will be understood that the specification and examples are illustrative 
but not limitative of the present invention and that other embodiments 
within the spirit and scope of the inventions will suggest themselves to 
those skilled in the art.