A PROCESS FOR THE PREPARATION OF A TRIMER ACIDS PRODUCT OF IMPROVED COLOUR

Abstract: In a process for the preparation of a trimer acids product of improved (lighter) colour than the starting product, a highly viscous trimer acids product of dark colour (Gardner colour (1963) greater than 13) is mixed with an amount of monocarboxylic acid which is sufficent to obtain a mixture of trimer acids and monocarboxylic acids having a viscosity low enough to allow in a following step of the process hydrogenation of the mixture of trimer acids and monocarboxylic acids in the presence of a hydrogenation catalyst and ready removal of the catalyst after hydrogenation, after which the hydrogenated mixture is separated by distillation in a first fraction containing predominantly monocarboxylic acid and a second fraction comprising trimer acids of a colour which is substantially lighter (Gardner colour (1963) smaller than 9) than the colour of the trimer acids starting product.

Description: A process for the preparation of a trimer acids product of improved colour. The present invention relates to a process for the preparation of a trimer acids product of improved colour. Trimer acid products comprising 80 wt% or more of trimer acids and higher polycarboxylic acids usually are obtained as a by-product of the dimerization of C 14 to C 2 unsaturated fatty acids and mixtures thereof, in particular such mixtures containing C 18 unsaturated fatty acids.The starting product for the dimerization process usually is a mixture of tall oil fatty acids, although other unsaturated fatty acids feedstocks may be used as starting products.The main product of the dimerization process are dimer acids.However the product of the dimerization process usually does not contain more than about 85 % by weight of such dimer acids, the remaining part consisting of trimer acids, higher polycarboxylic acids and some monomer acids (unchanged, cyclized, aromatized and isomerized monocarboxylic fatty acids) .For high demanding applications the relative amount of dimer acids in the dimerization product can be increased by distilling off the monomer acids as a first fraction (fore- cut) and the dimer acids as a second fraction (centre-cut) containing over 95% of dimer acids.The residue, which is high in trimer acids and higher polycarboxylic acids, has a very high viscosity making it nearly impossible to further process the residue at temperatures below the decomposition temperature, and has a colour which is usually objectionable, being too dark for most possible applications. A direct hydrogenation of trimer acids therefore is hardly possible, it requires a high amount of catalyst at a rather high temperature. he catalyst can only be separated from the hydrogenated product with difficulty. It is an object of the present invention to provide a process for the preparation of a trimer acids product of improved colour, the colour being lighter than the colour of a starting product high in trimer acids such as the residue obtained by a dimerizing process as described in the preceding paragraph, thereby broadening the spectrum of possible applications of the trimer acids product and precluding the disposal of an objectionable product harmful to the environment. It is a further object of the invention to provide a process allowing hydrogenation at a reasonable temperature and easy removal of the catalyst after hydrogenation. In "Fatty Acids in Industry", editor R.W.Johnson and E. Fritz (Marcel Dekker Inc; New York, 1989) page 161, last four lines, it has been suggested that a light-coloured, low- iodine value trimer acid product could be produced by the hydrogenation of a commercial dimer acid made from oleic acid, followed by separation of the dimer-trimer acid in a molecular still.No further details as to the process and about colour and viscosity of the resulting trimer acid product have been disclosed in table 7, page 167, referred to on page 161, last four lines.According to table 7, the trimer acid product only contains 60 % of trimer acids, rest dimer acids.A process as suggested cannot be used in case it is intended to produce non-hydrogenated dimer acids. In GB-A-999 732 (General Mills Inc.) a process has disclosed for the preparation of decolorized polymeric fatty acids in which the polymeric fatty acids are subjected to hydrogenation and distillation.The distillation may be conducted prior or subsequent to the hydrogenation.Products are obtained containing more than 90% of dimer acids of good colour.There is no reference, however, to the residue of the distillation containing trimer acid and higher polycarboxylic acids and to its colour, so that it may fairly be assumed that in case tall oil fatty acids are used in the production of dimer acids and the distillation is carried out after hydrogenation, the residue would have an objectionable dark colour and would be unfit for most possible applications. The invention now provides a process for the preparation of trimer acids of improved colour. In the process according to the invention a highly viscous trimer acids starting product of dark colour, such as obtained by dimerizing unsaturated fatty acids and distilling off monocarboxylic fatty acids and dimer acids according to a process known in the art, is mixed with an amount of monocarboxylic acid, which is sufficient to obtain a mixture of trimer acids and monocarboxylic acids, having a viscosity low enough to allow in a following step of the process hydrogenation of the resulting mixture of trimer acids and monocarboxylic acids in the presence of a hydrogenation catalyst and ready removal of the catalyst after hydrogenation, after which the hydrogenated mixture is separated by distillation in a first fraction containing predominantly monocarboxylic acid and a second fraction comprising trimer acids of a colour which is substantially lighter than the colour of the original trimer acids starting product. Any process known in the art for dimerizing fatty acids resulting in a mixture of dimer acids, monocarboxylic fatty acids and trimer acids may be used to obtain the trimer acids starting product of the invented process for obtaining a light-coloured trimer acids product. Dimerization may for instance be carried out in the presence of 4 to 10 wt% of a natural clay catalyst such as ontmorillonite clay at a temperature of 230 to 265 °C for 2 to 7 hours under a steam pressure of 2 to 10 bar.After completion of the dimerization process, the clay catalyst is usually removed by filtration, and the monocarboxylic fatty acid is removed by conventional vacuum distillation.A product containing a high amount of dimer acids may be obtained by wiped-film evaporation or molecular distillation.A process which is commercially utilized is for example described in Kirk-Othmer, Encyclopedia of Chemical Technology third.ed. , vol.7 page 771.Products containing dimerized and trimerized fatty acids are commercially available. Commercially available trimer acids products generally are highly viscous and have a dark brown colour such as products having a Gardner colour determined according to ASTM specification D 1544-63T, hereinafter referred to as "Gardner (1963)", of 13 or higher, such commercial products can be decolourized by the process according to the invention. The colour of the hydrogenated trimer acids product obtained with the process according to the present invention is a transparent dark yellow, lighter than Gardner colour (1963) 9, typically lighter than Gardner colour (1963) 8.The product may be used in the preparation of polymers such as polyesters and polyamideε, to be used in inks, coatings etc., in a pure form or mixed with dimer acids and monomer products. According to a preferred embodiment of the invention the trimer acids starting product of dark colour is mixed with a saturated monocarboxylic fatty acid or a mixture of such acids having 14 to 24 carbon atoms in their molecule.Heat may be applied to facilitate mixing, in particular in case monocarboxylic fatty acids which are solid at ambient temperature are used.Preferred saturated monocarboxylic fatty acids are palmitic acid and stearic acid and mixtures comprising such acids.It is however also possible to use the monocarboxylic acids mixture obtained in the distillation of the crude product of the dimerization of unsaturated fatty acids as a first fraction or fore-cut.Usually a mixture of low enough viscosity to allow hydrogenation in the presence of an effective amount of catalyst and ready removal of the catalyst from the mixture after completion of the hydrogenation, is obtained by mixing three parts by weight of the trimer acids starting product with one part by weight of monocarboxylic fatty acid.However smaller or greater relative amounts of monocarboxylic acid may be used, if desirable, to obtain a low enough viscosity for hydrogenation and subsequent removal of the catalyst for instance by filtration.A viscosity of between 200 and 300 mPa.s at 80 °C usually would be satisfactory in practice. The hydrogenation of the trimer acids - monocarboxylic acid mixture may be carried out in the presence of a metal catalyst such as nickel, copper, cobalt, platinum, palladium, rhodium and mixtures of these metals and other hydrogenation catalysts known in the art. The metal catalyst may be present on an inert carrier material such as kieselguhr, silica, alumina, aluminosilicates or carbon.It is not necessary to use a fresh catalyst in the process according to the invention. ithout any pre-treatment a catalyst which has previously been used for instance in the hydrogenation of unsaturated fatty acids after its recovery (so-called "spent catalyst") may be used as a catalyst in the process according to the invention.At viscosities of the mixture lower than for instance 250 mPa.s at 80 °C amounts of catalyst up to 0.050 wt% metal relative to the amount of the mixture can be used. Hydrogenation of the trimer acids - monocarboxylic acid mixture may be carried out in a known manner, for example in a dead-end autoclave into which hydrogen is led, while heating and agitating the contents of the autoclave. The present invention also relates to the use of the light coloured trimer acid product in the manufacture of polymers which are selected from the group consisting of polyesters (including alkyd resins) , polyamides, polyesteramides, polyurethanes, polyepoxides, and mixtures thereof. The invented process will now be explained in greater detail with reference to the following example. EXAMPLE A trimer acids starting product comprising 90 wt% of trimer acids, about 10 wt% of dimer acids and at least 0.5 wt% of monocarboxylic acids, which was obtained by dimerizing in a conventional way a mixture of fatty acids predominantly consisting of unsaturated C 18 fatty acids and distilling off the greater part of the dimerized fatty acids was subjected to the method according to the invention.The viscosity of the product at 80 °C was 1400 mPa.s and the trimer acids starting product had a Gardner colour (1963) of between 13 and 14. hree parts by weight of the starting product were mixed with one part by weight of a commercial product PRISTERENE 4963 (Trade Mark; ex Unichema Chemie B.V. , Gouda, The Netherlands a stearine comprising stearic acid and palmitic acid and having a titre of 52-56°C, an acid value of 198-203 and a saponification value of 199-204) .Mixing was done at a temperature of the constituents of about 100 "C.The mixture had a Gardner colour (1963) of between 12 and 13 and the viscosity was 213 mPa.s at 80 °C. 1500 g of the mixture was hydrogenated in a dead-end autoclave (volume 0.01 m 3 ) in the presence of a catalyst consisting of 2 wt% of finely divided palladium on coal as a carrier material.The total amount of palladium used in the hydrogenation was 0.025 wt% of metal relative to the weight of the mixture present in the autoclave.The catalyst had been used previously in the hydrogenation of unsaturated fatty acids material.Hydrogen pressure in the autoclave was maintained at 25 bar and the mixture present in the autoclave was stirred with a velocity of 600 RPM.The hydrogenation was carried out at a temperature of 235°C for 1 hour and 15 minutes. After removal of the catalyst by filtration the mixture had a Gardner colour (1963) of between 5 and 6. onocarboxylic acid was distilled off from the hydrogenated mixture at a pressure of 1 mm Hg and a temperature of 225 °C.The composition of the residue was 85 wt% of trimer acids, 5 wt% of monocarboxylic acids, rest dimer acids, it had a Gardner colour (1963) of between 6 and 7. The colour improvement cannot be explained by the somewhat greater amount of monocarboxylic acids present in the end product of the process as compared to the starting product.In the present embodiment a spent catalyst was used, identical results are obtained in case a fresh catalyst is employed.

Claims: CLAIMS 1. A process for the preparation of a trimer acids product of improved colour in which a highly viscous trimer acids starting product of dark colour is mixed with an amount of monocarboxylic acid which is sufficient to obtain a mixture of trimer acids and monocarboxylic acids having a viscosity low enough to allow in a following step of the process hydrogenation of the resulting mixture of trimer acids and monocarboxylic acids in the presence of a hydrogenation catalyst and ready removal of the catalyst after hydrogenation, after which the hydrogenated mixture is separated by distillation in a first fraction containing predominantly monocarboxylic acid and a second fraction comprising trimer acids of a colour which is substantially lighter than the colour of the original trimer acids starting product. 2. A process according to claim l in which a trimer acids starting product is used obtained as a residue in dimerizing unsaturated fatty acids and distilling off monocarboxylic fatty acids and dimer acids. 3. A process according.to claim 1 in which a trimer acids starting product having a Gardner colour (1963) of at least 13 is treated to obtain a trimer acids product having a Gardner colour (1963) of at most 9. 4. A process according to claim 3 characterized in that the starting product is treated to obtain a trimer acids product having a Gardner colour (1963) of at most 6. 5. A process according to claim 1, characterized in that trimer acids starting product of dark colour is mixed with a saturated monocarboxylic fatty acid or a mixture of such acids having 14 to 24 carbon atoms in their molecule. 6. A process according to claim 5, characterized in that the trimer acids starting product is mixed with a monocarboxylic fatty acids chosen from the group consisting of palmitic acid, stearic acid and mixtures thereof. 7. A process according to claim 5, characterized in that the trimer acids starting product is mixed with the monocarboxylic acids mixture obtained in the distillation of the product of the dimerization of unsaturated fatty acids as a first fraction or fore-cut. 8. A process according to claim 1, characterized in that three parts by weight of the trimer acids starting product is mixed with one part by weight of monocarboxylic fatty acid. 9. A process according to claim 1, characterized in that the hydrogenation of the trimer acids - monocarboxylic acid mixture is carried out in the presence of a metal catalyst. 10. A process according to claim 9, characterized in that the hydrogenation catalyst comprises a metal chosen from the group consisting of nickel, copper, cobalt, platinum, palladium, rhodium and mixtures of these metals. 11. A process according to claim 1, characterized in that the hydrogenation catalyst is a spent catalyst. 12. A process according to claim 1, characterized in that a mixture is prepared having a viscosity between 200 and 300 mPa . s at °C . 13. A process according to claim 12,characterized in that an amount of catalyst up to 0.050 wt% of metal relative to the amount of a mixture having a viscosity up to 250 mPa.s at 80 °C is used. 14. Use of a light-colored trimer acids product, obtained with a process according to claims 1 to 13 in the manufacture of polymers, selected from the group consisting of polyesters, polyamides, polyesteramides, polyurethanes, polyepoxides and mixtures thereof.

Inventors: POELS EDUARD KAREL, POELS, EDUARD, KAREL
Applicants: POELS EDUARD KAREL, UNICHEMA CHEMIE BV, POELS, EDUARD, KAREL, UNICHEMA CHEMIE B.V.
Application year: 1993
Main classification: C07C57
IPC codes: C07C51