LOW-VISCOSITY ESTER MIXTURES

Abstract

The invention relates to the preparation of low-viscosity ester mixtures for transesterification of vegetable or animal fats or oils with monofunctional esters.

Description

RELATED APPLICATIONS

This application claims benefit to European Patent Application No. 07019768.6, filed Oct. 10, 2007, which is incorporated herein by reference in its entirety for all useful purposes.

BACKGROUND OF THE INVENTION

The invention relates to the preparation of low-viscosity ester mixtures by transesterification of vegetable or animal fats or oils with monofunctional esters. The randomized transesterification of various triglycerides with one another, catalyzed with bases, acids or enzymes, is known and is described in Journal of the American Oil Chemists' Society (1953) 30, 320-325; Biotechnology and Bioengineering (2006) 94 (5), 877-887; Grasas y Aceites (2005) 56 (4), 267-275; Journal of Food Science (2005) 70 (6), C365-C372; JP 11225671; Fett/Lipid (1998) 98 (2), 60-65; Journal of Industrial and Engineering Chemistry (1948) 40, 1183-1190. This transesterification in turn leads to triglycerides having a comparably high viscosity and high solidification point. They are therefore not suitable, for example, as an auxiliary or additive or solvent for finishes.

Esters having low viscosity and low solidification point can be obtained by transesterification of triglycerides with monoalcohols to give fatty acid alkyl esters and glycerol. This procedure is also well known and is described in Bioresource Technology (2006) 98 (3), 639-647; Industrial & Engineering Chemistry Research (2005) 44 (25), 9535-9541; Chemical Engineering & Technology (1999) 22 (1), 70-75. A disadvantage of these processes is that glycerol forms as inevitable product which has to be separated off since, particularly when used as a solvent or additive in finishes, free OH groups are as a rule problematic owing to their reactivity, for example towards isocyanate groups.

Furthermore, the transesterification of triglycerides with carboxylic acids is known and is described in Tluszcze Jadalne (2002) 37 (1/2), 82-92. In this approach, the fatty acids eliminated have to be separated off after transesterification is complete, in order to obtain ester mixtures which can be used as solvents or diluents in coating technology.

Starting from the process described in the prior art, it is therefore the object of the present invention to provide a process, which is as technically simple as possible, for the preparation of esters or ester mixtures which are liquid at 23° C. with a viscosity of <50 mPa·s and have a solidification point of less than −10° C., and removal of compounds containing hydroxyl and/or carboxyl groups is dispensed with.

EMBODIMENTS OF THE INVENTION

An embodiment of the present invention is a process for preparing ester mixtures comprising reacting triglycerides with alkyl or cycloalkyl esters of aliphatic or cycloaliphatic monocarboxylic acids.

Another embodiment of the present invention is the above process, wherein said triglycerides are triesters of glycerol with C6- to C22-carboxylic acids.

Another embodiment of the present invention is the above process, wherein said triesters of glycerol are free of OH groups and have 6 or less olefinic double bonds.

Another embodiment of the present invention is the above process, wherein said alkyl or cycloalkyl esters are free of OH groups.

Another embodiment of the present invention is the above process, wherein said alkyl or cycloalkyl esters are linear or branched alkyl esters of monofunctional aliphatic carboxylic acids.

Another embodiment of the present invention is the above process, wherein said alkyl or cycloalkyl estersare butyl acetate, ethyl propionate, or mixtures thereof.

Another embodiment of the present invention is the above process, wherein said process is carried out in the presence of at least one catalyst.

Yet another embodiment of the present invention is an ester mixture prepared by the above process.

Another embodiment of the present invention is the above ester mixture, wherein said ester mixture have shear viscosities of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

Yet another embodiment of the present invention is a solvent comprising the above ester mixture.

Yet another embodiment of the present invention is a auxiliary comprising the above ester mixture.

Yet another embodiment of the present invention is a process agent comprising the ester mixture.

Yet another embodiment of the present invention is a fuel for internal combustion engines comprising the above ester mixture.

Another embodiment of the present invention is the above solvent, wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above auxiliary, wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above process agent, wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

Another embodiment of the present invention is the above fuel for internal combustion engines, wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

DESCRIPTION OF THE INVENTION

It has now been found that the transesterification of triglycerides with alkyl esters of aliphatic or cycloaliphatic carboxylic acids is possible and ester mixtures having the desired properties can be obtained thereby. It is particularly advantageous that neither OH-nor COOH-functional cleavage products are obtained, the removal of which will be necessary in particular for the field of use of additives for finishes.

The invention therefore relates to a process for the preparation of ester mixtures and the ester mixtures themselves thus obtainable, in which triglycerides are reacted with alkyl or cycloalkyl esters of aliphatic or cycloaliphatic monocarboxylic acids.

In the context of the invention, triglycerides are fats and oils of vegetable, animal and/or synthetic origin, preferably vegetable origin.

Preferred triglycerides are the triesters of glycerol with C6- to C22-carboxylic acids. Preferred triesters of glycerol of the abovementioned type have no free OH groups and furthermore have 6 or less, preferably 3 or less, olefinic double bonds.

Triglycerides of vegetable origin are, for example, palm oil, coconut oil, olive oil, rapeseed oil and oils of other seeds of cruciferous plants (carmelina, sea kale, turnip rape, mustard), sunflower oil, corn oil, cottonseed oil, peanut oil, hazelnut oil, poppy seed oil, linseed oil, safflower oil, thistle oil, coclebur oil, wood oil, soya oil and the oils of other seeds of papilionaceous plants (lupins, caragana), hemp oil, marigold oil, Iberian dragon's head oil, evening primrose oil, coriander oil, black cumin oil, jatropha oil, castor oil or physic nut oil. Preferred oils of vegetable origin are rapeseed oil, sunflower oil, palm oil and soya oil.

Triglycerides of animal origin are, for example, butter fats, lards, tallows, blubbers, fish oils or fish liver oils.

In principle, said triglycerides may be used in the process according to the invention individually or as any desired mixtures with one another.

The alkyl or cycloalkyl esters of aliphatic or cycloaliphatic monocarboxylic acids may also contain heteroatoms, such as oxygen in the form of ether groups, in the alkyl or cycloalkyl radical. Any desired mixtures of the alkyl or cycloalkyl esters may also be used.

The alkyl or cycloalkyl esters used for the transesterification are preferably free of OH groups.

Linear or branched alkyl esters of monofunctional aliphatic carboxylic acids are particularly preferably used.

These preferably have 1 to 10, particularly preferably 2 to 8, carbon atoms in the alkyl radical.

Preferably, the aliphatic carboxylic acids of the linear or branched alkyl esters of monofunctional aliphatic carboxylic acids have 1 to 10, preferably 2 to 8, carbon atoms.

In a preferred embodiment, the linear or branched alkyl esters of monofunctional aliphatic carboxylic acids are chosen so that the number of carbon atoms therein is at least 4.

Examples of linear or branched alkyl esters of monofunctional aliphatic carboxylic acids are n-butyl, isobutyl, 2-butyl, amyl, isoamyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl formate,

n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl acetate,

ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl propionate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl butyrate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl isobutyrate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl valerate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl pivalate,

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl capronate and

methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, amyl, isoamyl, methoxyethyl, ethoxyethyl, butoxyethyl, methoxypropyl, n-hexyl or 2-ethylhexyl ethylhexanoate.

Monoesters of the abovementioned type based on acetic acid or propionic acid are particularly preferred.

Butyl acetate and ethyl propionate are very particularly preferred, it also being possible to use any desired mixtures thereof.

The weight ratio of the triglycerides used to the monofunctional esters used is in general from 0.1 to 10, preferably from 0.1 to 3, particularly preferably from 0.5 to 2.

The reaction is preferably carried out in the presence of at least one catalyst, amounts of catalyst of 0.00001 to 0.3 part by weight, based on the mixture of triglyceride and monoester, being preferred.

The amount of catalyst is particularly preferably 0.00001 to 0.02 part by weight. If enzymes are used as catalysts, the amount is 0.001 to 0. 1 part by weight.

Catalysts in the context of the invention are, for example, alkali metal or alkaline earth metal carbonates, oxides, hydroxides or alcoholates, bismuth, tin, zinc, titanium, cobalt, iron, antimony or zirconium compounds, amidines, such as DBU or DBN, guanidines, such as tetra- or pentamethylguanidine, or amines, such as DABCO, the non-amine catalysts being preferred. The basic catalysts can be deactivated after the reaction by addition of acids, such as p-toluenesulphonic acid, or dibutyl phosphate. Catalysis by Bronsted acids is also possible but not preferred.

Enzymes in the context of the invention are lipases, but the chemical catalysts are preferred.

In principle, C1 to C18-alcohols may also be added in addition to the monoesters for the transesterification.

Examples of such alcohols are methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, diols, such as, for example ethylene glycol, diethylene glycol, triols and tetraols, such as, for example, glycerol, trimethylolpropane, pentaerythritol and/or mono- or diglycerides. Based on the amount of the monoester, such alcohols are however preferably used at most in amounts of 25% by weight. Particularly preferably, the addition of such alcohols is dispensed with.

In a preferred embodiment, the triglycerides are reacted together with monoesters and catalysts until a chemical equilibrium has been established.

The reaction temperature during the reaction is preferably 160 to 260° C.

Furthermore, antioxidants, such as hydroquinone, hydroquinone monoalkyl ether or sterically hindered phenols, can be added to the reaction mixture, generally in amounts of 0.01 to 0.5% by weight, based on the reaction mixture.

Optionally, monoester used in excess can remain in the ester mixture obtained after the process according to the invention or can be separated off.

After the unconverted monoester has been separated off, the ester mixtures preferably have shear viscosities of 12 to 50 mPa·s, particularly preferably 18 to 40 mPa·s, at 23° C.

After the unconverted monoester has been separated off, the ester mixtures preferably have solidification points below 0° C., particularly preferably −40 to −10° C.

The present invention furthermore relates to the ester mixtures obtainable by the present process and the use thereof as solvents, auxiliaries or process agents for coating materials, finishes, paints, adhesives, laminating materials, sealing materials, printing inks, inks, colorants, dyes, mordants, corrosion inhibitors and rust inhibitors, impregnating agents and graphic materials, as auxiliaries, plasticizers, levelling agents, reactive diluents, additives, in cosmetics or as cosmetic raw material, for the preparation of pharmaceutical formulations, as lubricants, anti-friction agents, release agents or coolants, as oil, in sunscreen agents, in or as diluents, cleaning agents or pretreatment agents, in foods of all types.

A likewise possible use of the ester mixtures obtainable according to the invention is the use as fuel or as an additive in fuels for internal combustion engines or as the oil phase of an oil-in-water emulsion which is used as a cooling lubricant in metal processing.

For the abovementioned fields of use, it is firstly unimportant whether or not the ester mixture still contains residual amounts of monoester used for the transesterification. It is preferable to separate off the monoester used for the transesterification after the end of the transesterification reaction.

If the ester mixtures according to the invention are used as fuel or as an additive in fuels for internal combustion engines, additives such as cetane number improvers, antioxidants, antifoams, corrosion inhibitors, flow improvers, surfactants or smoke reducers, can be added.

EXAMPLES

The determination of solids was effected by weighing on a dial balance from Mettler-Toledo at 125° C. to constant weight.

The GPC analysis (gel permeation chromatography) was recorded with THF as eluent. The evaluation was effected by determination of the peak area percentages.

The viscosity determination was effected using a cone-and-plate viscometer from Anton-Parr at 23° C. The viscosities are stated in the unit [mPa·s].

General Preparation Method

The mixture of 2000 g of soya oil, 1000 g of monofunctional ester, 1 g of dibutyltin oxide and 2 g of hydroquinone was heated in an autoclave under autogenous pressure for 16 hours to 200° C. The viscosity of the reaction mixture was measured before the reaction, after the reaction and after the removal of the unreacted ester of the formula I by distillation (in mPa·s). Furthermore, the solids content was measured by means of a dial balance at 125° C. after the reaction and after the removal of the unreacted ester of the formula I by distillation (in %). The composition of the reaction mixture was determined after the reaction by GPC (proportion of triglyceride, diglyceride monoalkanoate, monoglyderide dialkanoate and alkyl fatty acid ester in % by weight), the unreacted ester of the formula I not being detected by the method.

In all examples, the pour points of the reaction mixtures were −10° C. before the reaction and −30° C. after the reaction (measured by cooling in a refrigeration bath and occurrence of the first precipitate). Dry ice in acetone was used as the refrigeration bath. The temperature at which the precipitate formed in a test tube filled with 3 g of the sample was visually assessed.

The viscosity of the soya oil before the reaction was 57 mPa·s.

	Example
	1	2	3	4
Ester of the formula I	butyl	ethyl	ethyl	methoxyethyl
	acetate	butyrate	propionate	acetate
Viscosity before the	3	2	7	9
reaction
Viscosity after the	8	5	6	12
reaction
Viscosity after	28	37	31	20
distillation
Solids content
determined
Solids after reaction	72.8	68.5	71.1	72.3
Solids after distillation	97.5	99.5	98.9	96.4
Proportions in %
(according to GPC
analysis):
Triglyceride	38	68	55	45
Diglyceride	32	20	27	29
monoalkanoate
Monoglyceride	4	3	4	5
dialkanoate
Alkyl fatty acid ester	23	7	13	19

In a further experiment, the mixture of 8000 g of soya oil, 4000 g of butyl acetate, 4 g of dibutyltin oxide and 8 g of hydroquinone was heated in an autoclave under autogenous pressure for 16 hours to 240° C. The viscosity of the reaction mixture was measured after the reaction and after the removal of the unreacted ester of the formula I by distillation (in mPa·s). It was found that the viscosity after the reaction but before the distillation was 12.8 mPa·s. After removal of the butyl acetate, a viscosity of 20.8 mPa·s was found (solids content 99%).

From the experiments, it is evident that the reaction according to the invention results in a randomized transesterification which leads to ester mixtures having advantageous properties (low viscosity in combination with low pour point).

All the references described above are incorporated by reference in its entirety for all useful purposes.

While there is shown and described certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.

Claims

1. A process for preparing ester mixtures comprising reacting triglycerides with alkyl or cycloalkyl esters of aliphatic or cycloaliphatic monocarboxylic acids.

2. The process of claim 1, wherein said triglycerides are triesters of glycerol with C6- to C22-carboxylic acids.

3. The process of claim 2, wherein said triesters of glycerol are free of OH groups and have 6 or less olefinic double bonds.

4. The process of claim 1, wherein said alkyl or cycloalkyl esters are free of OH groups.

5. The process of claim 1, wherein said alkyl or cycloalkyl esters are linear or branched alkyl esters of monofunctional aliphatic carboxylic acids.

6. The process of claim 1, wherein said alkyl or cycloalkyl esters are butyl acetate, ethyl propionate, or mixtures thereof.

7. The process of claim 1, wherein said process is carried out in the presence of at least one catalyst.

8. An ester mixture prepared by the process of claim 2.

9. The ester mixture of claim 8, wherein said ester mixture has a shear viscosity of 12 to 50 mPa·s at 23° C. and solidification points below 0° C.

10. A solvent comprising the ester mixture of claim 8.

11. An auxiliary comprising the ester mixture of claim 8.

12. A process agent comprising the ester mixture of claim 8.

13. A fuel for internal combustion engines comprising the ester mixture of claim 8.

14. A solvent comprising the ester mixture of claim 9.

15. An auxiliary comprising the ester mixture of claim 9.

16. A process agent comprising the ester mixture of claim 9.

17. A fuel for internal combustion engines comprising the ester mixture of claim 9.