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Gupta A, Bowden NB.
ACS Appl Mater Interfaces. 2013 Feb 13;5(3):924-33.
Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
Abstract
This article describes the separation of mixtures of fatty acid salts using a new organic solvent nanofiltration membrane based on polydicyclopentadiene (PDCPD). Mixtures of free fatty acids could not be separated by the membranes because they permeated at similar rates. When triisobutylamine was added to the fatty acids, the cis-fatty acid salts (oleic, petroselinic, vaccenic, linoleic, and linolenic acid) had slower permeation though the membranes than saturated (stearic acid) and trans-fatty acid (elaidic acid) salts. The reason for the difference in permeation was due to the formation of stable salt pairs between the amine and fatty acids that increased their cross-sectional areas. The fatty acid salts derived from saturated and trans-fatty acids were smaller than the critical area cutoff for the PDCPD membranes, so they readily permeated. In contrast, the fatty acid salts derived from the cis-fatty acids had critical areas larger than critical area cutoff of the PDPCD membranes and had slowed permeation. The partitioning coefficients of fatty acids and fatty acid salts were investigated to demonstrate that they were not responsible for the difference in permeation. The use of pressure was investigated to greatly accelerate the permeation through the membranes. For a solvent mixture of 35/65 (v/v) toluene/hexanes, the permeation of solvent was approximately 39 L m(-2) h(-1). This value is similar to values reported for permeation through membranes used in industry. The separation of a mixture of fatty acids based on the composition of soybean oil was investigated using pressure. The saturated fatty acid salts were almost completely removed from the cis-fatty acid salts when iBu(3)N was used as the amine to form the salt pairs. The separation of the cis-fatty acids found in soybean oil was investigated with Pr(3)N as the amine. The oleic acid salt (oleic acid has one cis double bond) preferentially permeated the membrane while the linoleic (two cis double bonds) and linolenic (three cis double bonds) salts were partly retained. The separation of fatty acids using membranes may have real applications in industry to purify fatty acids on a large scale.
Additional Information
We recently developed the first membrane-based method to selectively extract individual fatty acids from a mixture of fatty acids. Specifically, we developed a method to extract stearic, oleic, linoleic, and linolenic acid from a mixture of all four fatty acids such that each fatty acid was isolated as a highly pure, individual component. This discovery is critically important because current methods to purify fatty acids are expensive and time consuming such that the cost of a pure (>98% purity) fatty acid is high. Thus, many applications of fatty acids begin with a mixture of four or more fatty acids derived from a natural source. Our method is a significant advance because, for the first time, fatty acids can be purified using a membrane. Separations using membranes are inexpensive and rapid such that our method can be used to quickly and inexpensively purify large amounts of fatty acids.
We used an organic solvent nanofiltration membrane that separated fatty acids based on their differences in sizes. An amine was added to a mixture of fatty acids to amplify the difference in sizes of the fatty acids, and the amines were readily recycled at the completion of each separation. The separations were fast (flux of 39 L m-2 h-1) and highly reproducible. We initially studied the separation of elaidic, stearic, oleic, linoleic, linolenic, vaccenic, and petroselinic acids with a high level of success. Although we have not explored other fatty acids, this method is highly versatile and can be applied to the purification of more polyunsaturated fatty acids.
We are currently exploring collaborations with industry or opportunities to license this technology. Any interested party should contact Ned Bowden ([email protected]) or Sean Kim ([email protected]).
