MEMBRANE CONCENTRATION AND SEPARATION OF L-ASPARTIC ACID AND L-PHENYLALANINE DERIVATIVES IN ORGANIC-SOLVENTS

The concentration and separation of the amino acids N-benzyloxycarbony l L-aspartic acid and L-phenylalanine methyl ester hydrochloride in or ganic solvents have been investigated using reverse osmosis membranes of two types of cellulose acetate, a nanofiltration membrane of polyam ide-polyphenylene sulfone (PA-PPSO) composite and a gas separation mem brane of polyimide composite in a stirred batch cell. The organic solv ents used included primary, secondary, and tertiary alcohols, an ester , and a ketone. There were significant variations in permeate flux, so lute rejection, and membrane stability. Usually the rejection of both amino acids was similar; however, certain membrane-solvent combination s gave significantly different levels of rejection. The highest reject ion of amino acids (similar to 0.94) at the lowest pressure of 0.5 MPa was obtained with the PA-PPSO membrane using methanol as a solvent. T he cellulose acetate membranes gave reasonable rejection and fluxes bu t the membrane stability was very poor. The performance of the polyimi de composite membrane was good with ethanol but poor with other solven ts. The PA-PPSO membrane with methanol as solvent appeared the most pr omising combination, and the separation performance according to conce ntration polarization was discussed.