SEPARATION OF AMINO-ACIDS BY NANOFILTRATION AND ULTRAFILTRATION MEMBRANES

The aim of this work was to determine the amino acid retention as a fu nction of concentration and the ionic composition of the feed for Vari ous polymeric membranes. Results from the Literature and the insights gained from our amino acid experiments were then applied to the separa tion of amino acid mixtures using nanofiltration and ultrafiltration m embranes. Attention was paid to the charge and size properties of the amino acids and the membranes and their effects on the separation. The separation was severely influenced by size exclusion and Donnan exclu sion effects, as expected. The size exclusion effect was predominant w ith the nanofiltration membrane tested, while Donnan exclusion effects were dominant with the ultrafiltration membranes. In the case of char ged amino acids, a dependence of their retention on their concentratio n and the salt composition was found. Amino acids carrying no net char ge acted as neutral species and were practically not influenced. Trend s observed with pure amino acids were also found with mixtures of amin o acids and it was shown that the selectivity of the separation of ami no acids can be manipulated by modifying the charged state of the amin o acid by changing the pH, or by modifying the salt composition of the feed solution. The highest selectivity of separation was obtained whe n Donnan exclusion was the dominating mechanism. (C) 1998 Elsevier Sci ence B.V. All rights reserved.