Kinetics of the extraction of phenylalanine and glutamic acid by ion-exchange carriers

Abstract

Biological transport of amino acids is usually mediated by carrier proteins buried in biomembranes. The application of models to such transport systems has long been desired in the separation science and technology of amino acids and is an active area of research. Recently, the application of commercial metal extractants as mobile carriers in the liquid membrane technology has attracted increasing attention due to their potential capability in the field of bioseparation. In the development of such a novel separation technique, knowledge of the extraction kinetics is necessary in addition to knowledge of the extraction equilibrium. Due to their zwitterionic character, it is possible to extract amino acids with ion-exchange carriers by controlling the pH of aqueous amino acid solutions. A modified Lewis-type cell experiment was used to study the extraction kinetics of glutamic acid (system I) and phenylalanine (system II) by naphthenic acid, and that of phenylalanine by a quarternary ammonium salt, Aliquat 336 (system III). The effects of agitation, interfacial area, carrier concentration, pH, and initial concentration of amino acids on the extraction rate were discussed. A rate equation involving the mass transfer terms was derived, based on an interfacial chemical reaction mechanism. It was found that the limiting case, based on an interfacial reaction rate-determining mechanism, was in good agreement with the experimental results. The intrinsic chemical reaction is controlled by the formation of an amino acid/ carrier complex at the interface. The mechanism of extraction proposed in this study is applicable to both glutamic acid and phenylalanine in the two ionic carrier systems.