Process for preparation of branched fatty acids

Details Process for preparation of branched fatty acids Process for preparation of branched fatty acids

1999-12-22

2001-07-03

Carr, Deborah D. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Fatty compounds having an acid moiety which contains the...

C554S150000

Reexamination Certificate

active

06255504

ABSTRACT:

The present invention relates to a process for the branching of fatty acids or derivatives thereof. Said fatty acids or derivatives thereof may be saturated or unsaturated, short (C8) or long (C24) chain.
Fatty acids are versatile building blocks in various parts of the chemical industry, ranging from lubricants, polymers, solvents to cosmetics and much more. Fatty acids are generally obtained by hydrolysis of triglycerides of vegetable or animal origin. Naturally occurring triglycerides are esters of glycerol and generally straight chain, even numbered carboxylic acids, in size ranging from 8-24 carbon atoms. Most common are fatty acids having 12, 14, 16 or 18 carbon atoms. The fatty acids can either be saturated or contain one or more unsaturated bonds.
Long, straight chain saturated fatty acids (C10:0 and higher) are solid at room temperature, which makes them difficult to process in a number of applications. The unsaturated long chain fatty acids like e.g. oleic acid are liquid at room temperature, so easy to process, but are unstable because of the existence of a double bond. The branched fatty acids mimic the properties of the straight chain in many respects, however, they do not have the disadvantages associated with them. For example branched C18:0 (commercially known as isostearic acid) is liquid at room temperature, but is not as unstable as C18:1, due to the absence of unsaturated bonds. Branched fatty acids are therefore more desirable for many applications compared to straight chain fatty acids. For example, mixtures of branched fatty acids having 8 to 16 carbon atoms are frequently used in the lubricants industry.
Apart from branched fatty acids other fatty acid derivatives, such as oligomerised fatty acids, find use in similar and other applications. Oligomeric fatty acids refer to materials prepared by coupling of the monomer units, of which typically dimeric and trimeric species are desired building blocks in plastics, the personal care industry, lubricants, etcetera.
Conventionally, branched fatty acids are obtained by isomerisation of the straight chain, unsaturated fatty acids. The reaction can be carried out using a clay catalyst, and is generally performed at high temperature (e.g. 250° C.). A common process is the preparation of branched C18:0 (iso-stearic acid) from unsaturated straight chain C18:1 (or also C18:2).
These conventional processes suffer from a number of disadvantages. A first disadvantage is the fact that unsaturated fatty acids or the derivatives thereof can be converted to branched fatty acids, but saturated fatty acids (or derivatives) are usually not converted by the conventional processes. Hence, a source will be needed containing a relatively large concentration of unsaturated fatty acids, which limits flexibility. Although many sources of fatty acids contain unsaturated fatty acids together with saturated fatty acids, it is disadvantageous to separate the unsaturated from the saturated fractions due to high associated costs.
Although there are a number of sources available containing abundant unsaturated straight chain fatty acids, this relates predominantly to C18:1, C18:2, C18:3, and to a lesser extent C16:1. The smaller fatty acids C10, C12 and C14 do not occur widely in nature in an unsaturated, straight chain form. Thus, applying the conventional process for the preparation of the branched, saturated corresponding fatty acids (i.e. branched short chain fatty acids, C8-C16) is not possible from long chain (C18 and longer) fatty acids.
Yet a further disadvantage is that the current branching process as set out above is only possible using relatively high temperatures (at about 250° C.).
Hence, there is a need for a process for the preparation of branched fatty acids, in which these compounds are formed by branching/isomerisation of a source comprising fatty acids, which may be saturated or unsaturated, branched or straight chain or a mixture thereof. Also, there is a need for a process for the preparation of branched fatty acids having a chain length of 8 or more carbon atoms, but less than 18 carbon atoms.
It has now been found that the above objectives can be met by a process for the branching of fatty acids, wherein a source comprising fatty acids or derivatives thereof, is contacted with an ionic liquid.
An ionic liquid is herein to be understood as a salt (or a mixture of salts) in its liquid form (i.e. molten).
Since mixtures comprising both saturated fatty acids and unsaturated fatty acids can be converted, the process may suitably be employed using a source which contains both saturated and unsaturated fatty acids. Depending upon the availability and price of the source material, it is preferred that the source comprises at least 20%, but preferably more than 50% by weight of saturated fatty acids or derivatives thereof. It is also preferred that at least 50% by weight of said fatty acids or derivatives of fatty acids in the source material have a fatty acid chain length of between 8 and 24 carbon atoms. A preferred fatty acid in this respect is stearic acid or derivatives thereof.
Simple derivatives of fatty acids may be converted using the process according to the invention in a similar way as the fatty acids themselves. For some purposes, such derivatives may be preferred. Regarding such derivatives in the source as mentioned, esters are preferred, with alkylesters being the most preferred. Of these alkylesters, the most preferred ones are the fatty acid esters of alcohols having 1-4 carbon atoms, e.g. methanol, ethanol, propanol. Hence, a preferred source for performing the reaction according to the invention comprises stearic acid, methyl stearate, and/or ethyl stearate.
The above indicates that a source containing a wide variety of fatty acids (containing both saturated and unsaturated fatty acids, branched and straight chain fatty acids) can be converted. This one of the most surprising results and is a considerable advantage over the known processes. Yet a further advantage is that there is no need to carry out the reaction at elevated temperatures: as long as the temperature is high enough for the salt which is used as the reaction “solvent” (or medium) to be in its liquid form (i.e. molten).
With respect to the type of ionic liquid, a wide variety of possibilities exists. However, it will be clear that the preferred ionic liquids are the ones that are liquid at relatively low temperatures. Although some salts have very high melting points (i.e. common NaCl has a melting point of approx. 850° C.), there are salts known which melt under less severe conditions. An example of such salts are mixtures of two or more salts. In the case in which a mixture of two salts is used, the resulting ionic liquid is called a binary ionic liquid. Hence, it is preferred that in the process as set out above the ionic liquid comprises a binary ionic liquid.
Preferred binary ionic liquids comprise a metal(III) chloride and/or an organic halide salt, e.g. [A]
+
X
−
. Also, inorganic halide salts can be used. Suitable metal(III) chlorides include aluminium(III) chloride and iron(III) chloride. Regarding the organic halide, an unsymmetrical imidazolium or pyridinium halide has the advantage that isomerisation may now occur under mild conditions, contrary to conventional processes. A preferred unsymmetrical imidazolium halide is 1-methyl-3-ethylimidazolium chloride.
Oligomerisation can occur as a side reaction. Depending upon the operating temperature chosen, around 20-30% oligomerised products (mainly dimers and trimers) are formed, together with 40-60% long- and short chain branched fatty acids. Generally speaking, the higher the operating temperature, the more the balance shifts from branched fatty acids towards oligomerised fatty acids. Although oligomerised fatty acids, in particular dimers, are usefule products themselves, generally speaking the formation of branched fatty acids will be the primary objective.
Therefore, it is preferred that the process according to the invention is carried out at temperatures b

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