Process for oligomerization of polyunsaturated acids and esters, products obtained and use thereof

For the oligomerization of a fatty ester or fatty acid containing conjugated double bonds, the reaction uses a catalyst consisting of an activated earth, e.g., montmorillonite, at a temperature of from 100.degree.-180.degree. C., preferably from 130.degree.-160.degree. C. The process can be carried out continuously or in a batch process on a fixed bed and is particularly applicable to conjugated methyl esters obtained by conjugating and transesterifying sunflower seed oil. The oligomerized products obtained are particularly useful as lubricants or polycondensation reactants.

BACKGROUND OF THE INVENTION 
The present invention relates to a novel process for oligomerization of 
fatty esters and acids of polyunsaturated oils. More precisely, it is 
concern with a process for the production of dimers and trimers at low 
temperatures and with small quantities of catalyst from any 
polyunsaturated ester or acid whose double bonds are conjugated or 
conjugatable. 
Dimers or trimers obtained from acids or esters may be used as base 
materials in the production of lubricants, polyamide monomers, amide type 
anticorrosive agents, or paint additives. 
The preparation of fatty acid dimers or oligomers from monoenyl, dienyl or 
trienyl fatty esters or acids is known. Activated earths (also called 
"activated clays") containing various additives (water, acid, chlorinated 
derivative, lithium salt, etc.) are currently employed as catalysts. 
British patent document GB 2 172 597 and the article published by J C 
COWAN in J.A.O.C.S. Vol 39, 1962, pages 534-545, describe the syntheses. 
The disadvantages of this technique are known. The reaction requires from 
6 to 10% by weight of activated earth with respect to the product to be 
oligomerized and this earth is lost. Temperatures of 220.degree. to 
250.degree. C. and reaction times of 6 to 8 hours are required. Filtration 
is difficult. When starting from polyenyl structures, the products 
obtained are in part aromatic. The cloud point of these compounds produced 
from a polyenyl acid is not very low. It is thus preferred to use monoenyl 
extracts of tallow. Finally, the resulting acidity when starting from 
esters is often high, whatever the ester employed. 
Lubricant bases cannot be manufactured using this synthesis. Fatty acids 
form by ester hydrolysis which necessitates that the fatty acids be 
esterified before any hydrogenation that may be required. In addition, the 
monomers must be distilled off since not only do these monomers have low 
molecular weights but, even in the absence of hydrogenation, a large 
quantity of saturated derivatives is also produced during the course of 
the reaction. The esters of the dimers and oligomers are then 
transesterified with a higher alcohol if starting from methyl esters. The 
manufacture of a lubricant base is thus a relatively lengthy process, and 
it would be of advantage to simplify the process. 
The literature records attempts to manufacture diners or oligomers at low 
temperature (120.degree.-180.degree. C.) (French patent FR 2 202 874). 
However, the process used does not appear to be very attractive. The ion 
exchange resin used, which is only active towards dienes and trienes, 
gives rise to a significant amount of ester hydrolysis despite the 
relatively low temperature (130.degree.-140.degree. C.), bringing the 
acidity to acid values which may reach from 12 to 30. The product obtained 
is quite colored and the resin rapidly loses activity. Finally, the 
dimer/trimer weight ratio is close to 1, while a good value generally 
obtained with activated earths is on the order of 4 to 5. Dimers rather 
than trimers are in demand for numerous applications. 
In one example in the literature, low temperature oligomerization of fatty 
acid esters is effected using almost 10% by weight of activated earth; 
however, in this instance the esters of very rare oils are used, such as 
esters of China wood oil or oiticica oil (British patent document GB-A 1 
466 418). These esters are double bonded trienes with 
trans-configurations. These structures are deemed to be very 
polymerizable. 
Finally, German patent document DE 1 268 616 mentions the use of conjugated 
polyunsaturated esters in a co-oligomerization reaction of esters and 
coumarone or indene in the presence of activated earths between 40.degree. 
and 180.degree. C. In this patent document, it is indicated that there is 
no homopolymerization of the conjugated esters since the saponification 
values of the products which are not monomers, after distillation, are 
very different from those of the dimers. 
SUMMARY OF THE INVENTION 
The invention, which differs from the prior art describing the use of 
activated earths on non-conjugated esters and at high temperature, 
proposes the use of an activated earth in the presence of polyunsaturated 
conjugated esters or acids (or which have been conjugated, for example, by 
an alkaline route) at a lower temperature. The compositions produced are 
particularly interesting, in particular as lubricant bases. The technique 
of the invention also has the advantage of being easier to carry out. 
Surprisingly, the reactivity of the conjugated esters does not appear to 
have excited the interest of those using activated earths, who have not 
detected the novel properties of the products formed under these 
conditions, nor the economic advantages which this technique represents. 
Because of the combined use of conjugated compounds as base material and 
activated earth as catalyst, it is possible to dimerize in less time at a 
lower temperature using less earth, but above all to operate continuously 
to produce a particularly advantageous dimer. 
The invention thus provides a process for oligomerization of at least one 
fatty ester of a 1 to 12 carbon atom alkyl or at least one fatty acid to 
produce a mixture comprising mainly dimers and trimers, the process being 
characterized in that the starting ester or acid containing conjugated 
double bonds (or bonds which have been conjugated) is brought into contact 
with an activated earth at a temperature of 100.degree. to 180.degree. C., 
preferably 130.degree. to 160.degree. C. 
Polyunsaturated fatty acids and polyunsaturated alkyl fatty esters to be 
considered are generally mixtures corresponding to natural, vegetable or 
animal, predominantly polyunsaturated oils or fats, derived therefrom by 
transesterification (for example, by basic catalysis) by means of an 
aliphatic monoalcohol having 1 to 12 carbon atoms (for the esters) or by 
hydrolysis (for the acids). The esters and acids under consideration may 
have, for example, from 12 to 22 carbon atoms in their acid portions. The 
mixtures of acids and esters used thus comprise polyunsaturated chains 
with, for example, 2 or 3 ethylene bonds of which some may be conjugated 
or conjugatable, as well as monounsaturated or saturated chains. 
Preferably, mixtures are used wherein the esters or acids have mainly 
polyunsaturated chains. 
Examples of polyunsaturated esters or acids with conjugated or conjugatable 
double bonds are those extracted from fish oils, sunflower seed oils, 
safflower oil, soya oil, linseed oil, tobacco oil, corn oil, grape seed 
oil, or any oil containing polyunsaturated compounds. 
The process of the invention advantageously uses as a starting material a 
methyl ester or the ester of a higher alcohol such as, for example, a high 
alcohol which may be used, as will be shown below, to transesterify the 
mixtures produced by the inventive process when the residual monomers are 
not separated out and when it is nevertheless desirable to use the product 
as a lubricant base. When the unconverted monomers are separated out of 
the reaction mixture, it is preferable to use esters of low molecular 
weight alkyls, for example having 1 to 4 carbon atoms. 
In the description that follows, a high alcohol is intended to mean a 
monofunctional or difunctional alcohol with an aliphatic chain which 
contains a larger number of carbon atoms than the alkyl group of the 
starting ester. Depending on the case, the high alcohol may be selected 
from butanol, 2-ethylhexanol, C7 or C13 oxo alcohols, diols such as 
ethyleneglycol, neopentylglycol, propyleneglycol, etc. 
The proportion of dimers in the product obtained is generally greater than 
that of the trimers. The product may also contain unreacted monomers. 
The ester dimer obtained is less acid, in general AV&lt;6 (AV=acid value). The 
yield may be greater than 60% in the case of conjugated methyl esters from 
sunflower seed. The remaining monomer contains few saturated derivatives 
and it is possible in certain cases to obtain, for certain uses, mixtures 
of monomers, dimers and oligomers with a sufficient viscosity and very low 
cloud point without the need to distill the monomers. In the prior art, 
when activated earths are used with monoenyl esters at high temperatures, 
crystallizable saturated compounds may be formed which have to be 
separated out. 
If the monomers are distilled off in the process of the invention, a very 
clear mixture of dimers and trimers is obtained which can readily be 
transesterified, and whose initial acid value (AV) is low, for example 
less than 6. 
When it is desired to use the inventive process to manufacture a lubricant, 
distillation of the monomers is also unnecessary and after 
transesterification with a high alcohol, a fairly stable oil can be 
produced. 
The higher the proportion of polyunsaturated acids or esters in the 
starting substrate, the greater the conversion. Furthermore, conjugation 
of dienes or trienes is generally effected by different methods, for 
example with potassium alcoholates for esters, or with hot soda for fatty 
acids. 
It should be noted that if the monomers are not distilled off following 
dimerization, the conjugation catalyst can be used to transesterify the 
starting methyl esters with a high alcohol, followed by dimerization of 
the high esters. 
More specifically, in the inventive process a montmorillonite based 
activated earth catalyst is used. This earth has generally been treated 
with mineral acids. Many of these earths are used commercially as bleach 
bases and are extremely inexpensive. Additives may be combined with these 
earths (water, alcohol, magnesium or lithium salt, organic acid or 
sulphuric acid). Tonsil, Prolit, K10, etc (registered trademarks) are 
examples of commercial names of such earths. 
The earths may be used in microsphere form, pellet form, or as extrusions, 
all of which are of use in a continuous process. Because of the relatively 
low operating temperature, fairly long lifetimes are possible. If the 
catalyst becomes deactivated, it can be reactivated by passage of an inert 
solvent, such as an aliphatic or cycloaliphatic hydrocarbon. 
The inventive process may be carried out continuously or in a batch 
process. 
In the continuous process, the conjugated ester or acid is generally passed 
one or more times through a column heated to 100.degree.-180.degree. C., 
more particularly to 130.degree.-160.degree. C., generally at a flow rate 
of from 1 to 5 volumes of ester or acid per volume of catalyst per hour 
(VVH=1 to 5). At the exit, filtration is carried out if required and 
transesterification is effected using a high alcohol, or the monomers are 
first distilled off and then transesterification is carried out. The 
monomers are mainly constituted by esters of oleic acid and saturated 
acids which are present at startup. The saturated derivatives could be 
first eliminated and the dienes concentrated by crystallization of the 
least unsaturated fatty acids or esters from methyl alcohol, acetone or 
hexane. 
The monomer fraction distilled off may have a number of uses, including use 
as a substrate for subsequent dimerization under different conditions. 
Ideally, however, the monoenes should be transformed into dienes by 
dehydrogenation. 
The batch process consists in mixing the conjugated ester or acid and 
activated earths and heating for the required time to effect conversion. 
The reaction time is generally from 1 h to 4 h. 
The temperatures are generally between 100.degree. and 180.degree. C., 
preferably 130.degree. to 160.degree. C. Concentrations are generally from 
1 to 10% by weight, preferably from 1 to 4% by weight, of activated earth 
with respect to the substrate to be oligomerized. 
At the end of the reaction, either the mixture of monomers, dimers and 
trimers is used, or the monomers are separated out, for example by 
distillation. As indicated above, transesterification may be carried out 
using a high alcohol.

The following examples illustrate the invention but are not limiting. 
Example 3 is given by way of comparison. 
EXAMPLE 1 
8 g of Tonsil FF activated earth was added to 200 g of the methyl ester of 
sunflower seed oil containing 62% of cis-trans conjugated linoleic ester. 
The mixture was heated with stirring to 135.degree. C. in an argon 
atmosphere. After 1 hour of reaction the following uncorrected values were 
obtained (in weight %) using gel permeation liquid chromatography (GPC): 
______________________________________ 
Trimers and + 19.5 weight % 
Dimers 47.2 weight % 
Monomers 34.3 weight % 
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Conversion was the same after 4 h. Flash distillation at 205.degree. C. 
under vacuum gave 51% by weight of monomers. Analysis of these monomers 
showed the presence of 19.2% by weight of conjugated dienes still capable 
of being transformed into dimers and 3.4% by weight of linoleic acid, the 
remainder being monoenes and saturated esters. The dimer acidity was low, 
of the order of 2.9% by weight; that of the substrate before distillation 
being 2.7% by weight. 
EXAMPLE 2 
The same example was effected under a vacuum of 15 mm of mercury 
(2.10.sup.3 Pa) using a filter pump. The following results were obtained 
using GPC analysis (gel permeation liquid chromatography). The values 
given are uncorrected, (% by weight): 
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Monomers Dimers Trimers 
______________________________________ 
1 h 36% 48% 16% 
3 h 31.5% 48.5% 19.6% 
4 h 34.4% 45.7% 19.7% 
5 h 34.7% 45.3% 19.9% 
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Analysis of the monomers by CG (vapour phase chromatography) in weight % 
was as follows: 
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C.sub.16 :0 = 12.7% 
C.sub.18 :0 = 7.6% 
C.sub.18 :1 = 29.0% 
C.sub.18 :2 unconj = 3.4% 
butyl esters = 9.0% 
C.sub.18 :2 conjugated = 21.0% 
others = 17.3% 
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Oleic acidity was 2.1 weight % for the distilled monomers. 
EXAMPLE 3 
(comparison) 
Treatment of the unconjugated methyl ester of sunflower seed oil under the 
same conditions as in example 1 resulted in no dimerization, even after 6 
h at 135.degree. C. using 4% by weight of activated earth. 
EXAMPLE 4 
1300 g of conjugated methyl esters of sunflower seed oil was heated with 52 
g of montmorillonite type activated earth. At 150.degree. C., the 
following results were obtained (weight %): 
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Dimers + trimers 
______________________________________ 
1 h 58.2% 
2 h 63.8% 
3 h 64.2% 
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Uncorrected results using GPC. 
After filtering using a no. 4 frit, a clear yellow product was obtained. 
The acidity was 3.7 weight %. Half of the product was set aside; the other 
half was distilled at 208.degree. C. under a vacuum of 1-2 mm of mercury 
(1.33.10.sup.2 to 2.67.10.sup.2 Pa). From 600 g of starting substance, 301 
g of a mixture of dimers and trimers was obtained. This product was 
transesterified using 2-ethylhexyl alcohol using a known technique, as was 
the undistilled product consisting of a mixture of monomers, dimers and 
trimers. 
The following results were obtained: 
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Monomers + Dimers + 
Trimers Dimers + Trimers 
2-ethylhexyl esters 
2-ethylhexyl esters 
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viscosity, mm.sup.2 /s at: 
40.degree. C. 
29.4 99.9 
100.degree. C. 
6.4 13.9 
viscosity index 
179 141 
flow point (.degree.C.) 
-24 -51 
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The mixture containing monomers remained liquid above -24.degree. C. 
EXAMPLE 5 
Conjugated methyl ester of sunflower seed oil was passed through a column 
filled with 20 cm.sup.3 of granules of modified alkaline earth 
montmorillonite at an hourly rate of 20 cm.sup.3 and at 150.degree. C. The 
product obtained was partially converted. GPC gave 52.3% by weight of 
monomers, 24.3% by weight of dimers and 22.1% by weight of trimers. The 
catalyst was very stable. On repassing the product, the yield was 
increased to 60% by weight of a mixture of dimers/trimers; after passage 
of 1500 cm.sup.3 of product, no drop in activity could be detected. This 
example shows the advantage of being able to operate at a lower 
temperature, since the catalyst is much more stable at this temperature. A 
clear yellow product exits. It has low acidity, no filtration is needed. 
Thus, using a 10 liter column, 240 liters of a mixture of monomers, dimers 
and trimers can be produced per day.