Separation of ethyl esters of eicosapentaenoic acid and docosahexaenoic acid by circulating liquid membranes using silver nitrate as a carrier. Uphill transport by use of temperature and solvent dependencies of distribution ratio

Experiments on the separation of ethyl ester of eicosapentaenoic acid (EPA-Et) and that of docosahexaenoic acid (DHA-Et) contained in ethyl ester of bonito oil (bonito oil-Et) were performed using circulating liquid membranes (CIRLMs) containing silver nitrate as a carrier. In this liquid membrane system an aqueous silver nitrate solution was circulated between a stirred vessel containing an organic solution of bonito oil-Et and another stirred vessel containing a receiving organic solvent. Using the CIRLM, two types of uphill facilitated transport of EPA-Et and DHA-Et in bonito oil-Et were demonstrated. The first type utilizes the distribution ratio of EPA-Et and DHA-Et, defined as the ratio of the concentration in the aqueous phase to that in the organic phase at equilibrium, which is remarkably dependent on the temperature, and the second uphill transport was based on the fact that the distribution ratio is considerably dependent on the solvent of the organic phase. A model of permeation through the circulating liquid membrane was proposed to explain the experimental results.