ENRICHMENT OF AN AMINO-ACID BY MICELLAR-ENHANCED ULTRAFILTRATION

It is difficult to enrich low molecular weight solutes by membrane pro cesses with sufficient speed under low applied pressure. However, comb ination of a solute with micelles of a surfactant enables enrichment o f the solute into the retentate solution by ultrafiltration. The micel lar-enhanced ultrafiltration of an amino acid, L-tryptophan, was carri ed out in a batch-stirred cell. The characteristics of the ultrafiltra tion of the micelles were examined with respect to the permeation flux and micelle rejection. As the concentration of the micelle-forming su bstance, cetylpyridinium chloride monohydrate (CPC; MW 358), in the re tentate solution increased, the permeation flux decreased but the conc entration in the permeate solution was limited. The effect of membrane molecular weight cut-off (MWCO) on permeation flux was obvious at low CPC concentrations but only slight at high concentrations. L-Tryptoph an (MW 204) combined with CPC micelles to be retained by membranes of MWCO 20,000 as well as MWCO 10,000; there was no difference in rejecti on between the two membranes. The rejection coefficient was estimated as a function of the solubilization constant and the micelle concentra tion. The rejection coefficient increased with increasing CPC concentr ation but too high CPC concentrations resulted in the leakage of CPC i nto the permeate solution.