Recovery of polyunsaturated fatty acids from urea adducts

Details Recovery of polyunsaturated fatty acids from urea adducts Recovery of polyunsaturated fatty acids from urea adducts

2002-04-03

2003-03-04

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...

C554S184000, C554S185000, C554S205000

Reexamination Certificate

active

06528669

ABSTRACT:

This invention relates to a method for recovering polyunsaturated fatty acids from urea adducts with mixed saturated and unsaturated fatty acids or esters or amides. The invention has particular, although not exclusive, application to the recovery of polyunsaturated fatty acids
from urea adducts formed during commercial processes for concentrating such acids from fish and vegetable oils.
In this specification and claims the term “fatty acid” is used in the sense that the fatty acid may be in the form of the free fatty acid or a fatty acid ester, especially esters with C
1
-C
4
alcohols, or a fatty acid amide. The same applies when any fatty acid is discussed using its proper name or an abbreviation thereof, such as for instance eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
It has been known for many years that urea forms complexes with organic compounds with long straight chains of carbon atoms, and moreover that the amount of urea required for such complex formation increases proportionately with the carbon chain length (Marschner, “The Story of Urea Complexes”, Chemical & Engineering News, 33, No. 6, Feb. 7, 1955, pps 494-6). Such urea adduct formation is employed industrially to separate wanted from unwanted components in the recovery of omega-3 polyunsaturated fatty acids, or mixtures thereof, from fish oils, as described by Breivik et al in the paper “Production and Quality Control of n-3 Fatty Acids” in “Fish, Fish Oil and Human Health”, published by W. Zuckschwerdt Verlag GmbH, Munich, 1992.
There is a growing demand for polyunsaturated omega-3 fatty acids and fatty acid mixtures, particularly for EPA and DHA which are increasingly being shown to play an important role in human and animal health and well-being. Commercially, compositions with high concentrations of EPA and/or DHA are obtained from fish oils. Partially processed fish oils which contain relatively high concentrations of EPA and DHA (up to about 30% EPA+DHA) are commercially available, but these oils contain many other similarly long chain unsaturated (mono- and poly-) and saturated fatty acids, and further complex and costly processing is necessary in order to recover EPA and DHA in desired concentrations, which depend on the intended use but which may typically vary from about 50% EPA+DHA for a health supplement up to 90% or higher EPA+DHA for pharmaceutical use. In some cases substantially pure EPA and/or DHA are needed.
At the same time as the demand for purified fish oil products such as concentrates of EPA and DHA is growing so the supply of partially processed fish oil containing relatively high concentrations of EPA and DHA is becoming increasingly scarce and hence more costly. There is thus a general need to ensure that the desired components eg EPA and DHA are recovered from the raw material to the greatest extent possible, and that wastage of these valuable fatty acids should be minimised. It would also be desirable to reduce the high cost of purifying fish oils.
As already mentioned, urea fractionation is used commercially in the processing of fish oils to recover desired omega-3 fatty acids. In a typical process the fish oil is first hydrolysed to convert the glycerides to fatty acids or transesterified, most often with ethanol, to form fatty acid esters. A processing step which removes short chain fatty acids or esters, commonly molecular distillation, may then be employed. Either before, but more usually after, the molecular distillation step, a urea fractionation is performed to further increase the concentration of the desired long chain polyunsaturated fatty acids. Stepwise urea fractionation may be carried out where the product from a first fractionation is used as feed in a second or further fractionation. Subsequently, molecular distillation, bleaching and/or chromatography, or other processing, is often employed in order to produce a product with the desired qualities.
Urea fractionation may also be employed to increase the concentration of polyunsaturated fatty acids from certain vegetable oils, for instance in a process for recovering &ggr;-linolenic acid in high concentration from evening primrose oil, borage oil or blackcurrant seed oil (see eg “Fractionation of Blackcurrant Seed Oil” by Traitler et al, JAOCS, 65, No. 5, May 1988).
In a typical commercial plant for manufacturing concentrated omega-3 fatty acids from fish oil the urea fractionation serves to increase the total EPA+DHA concentration from about 50% to about 80% by weight. The urea adduct which precipitates out contains a significant concentration, typically about 25-30% by weight, of fatty acids although the precise composition is highly dependent on where the urea fractionation is-employed in the manufacturing process. These fatty acids, which may be in free acid form or in the form of esters, are mainly saturated or monounsaturated fatty acids but they also include significant amounts of polyunsaturated fatty acids as well, typically up to 30-40% by weight of-the fatty acid fraction in the adduct. Currently, this urea adduct is treated as a by-product of the refining process, which may be used as an agricultural fertilizer, but in view of the growing scarcity and increasing expense of fish oils, and of the high cost of processing them, it would be desirable to be able to recover the valuable polyunsaturated fatty acids from the urea adduct in an economically worthwhile manner. Such a process would also desirably permit the recovery of the urea in a condition suitable for direct recycling.
It is known that urea adducts with fatty acids decompose when heated to about 130° C. or more. The freed fatty acids form a distinct layer in the separation vessel above the molten urea, and these two layers are readily separated. However, heating the urea adduct above 130° C. is liable to cause oxidation and decomposition of the polyunsaturated fatty acids, while urea itself is also somewhat unstable at high temperatures and may form by-products such as biuret. In any case, the concentration of polyunsaturated fatty acid in the fatty acid fraction which is recovered is only the same as the concentration of these fatty acids in the urea adduct. Moreover, the separated urea requires regranulation before it can be recycled to the urea fractionation step.
It is also known to recover the bound fatty acids from the urea adducts by heating with non-polar solvents, e.g. hydrocarbons such as isooctane. The fatty acids are extracted by the solvent, and can then be recovered by distillation of the solvent. However, this process involves use of very large quantities of solvent, which would not be acceptable on the commercial scale, and moreover does not lead to the direct recovery of the wanted fatty acids e.g. EPA and DHA. The urea itself becomes contaminated with the solvent, which means that a solvent removal step must be included if the urea is to be recycled, and the fatty acid fraction also may contain traces of the solvent which for many purposes would be unacceptable.
There thus is currently no simple, economically attractive process available for recovering desired polyunsaturated fatty acids from the urea adducts.
It is known to use supercritical fluids as selective solvents in various extractive processes. A supercritical fluid is a compound which under normal atmospheric conditions may be either a liquid or a gas but which above a critical temperature and pressure has a density comparable to that of a liquid while exhibiting a diffusivity, that is transport properties, of a gas. This combination of properties results in a fluid with good solvent properties which moreover can be varied over a wide range by varying the pressure and temperature of the supercritical fluid. Carbon dioxide is widely used as a supercritical fluid as its critical temperature and pressure (31° C., 74 bar) permit processing under acceptable conditions, and it is inert, non-toxic and cheaply and readily available.
It has been shown that the urea fractionation itself can be performed using supercritical CO
2
as a solvent.

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