Separation of polyunsaturated fatty acids with silver nitrate using a hollow-fiber membrane extractor

Solvent extraction of ethyl esters of polyunsaturated fatty acid such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was performed with an aqueous silver nitrate solution using a microporous hydrophobic hollow-fiber membrane extractor, The mixture of four kinds ethyl esters of fatty acids involved in fish oil was employed as a model solution of fish oil. Also studied was the extraction equilibria of these fatty acids at various conditions. It was demonstrated from the experimental results that EPA and DHA ethyl esters could be satisfactorily separated from ethyl esters of lower fatty acids such as oleic and palmitic acids. In addition, the effects of silver and ester concentrations in aqueous and organic feed solutions on the apparent permeabilities of fatty acids ethyl esters were investigated in extraction and stripping stages, respectively. It was concluded that the permeation rate was controlled by the diffusion across the membrane and the laminar boundary layer in the inner and outer sides of the hollow fiber.