STUDY OF REACTIVE EXTRACTION AND STRIPPING OF AMINO ACIDS

Abstract

With the growing demand of L-phenylalanine as a raw material for a new peptide sweetener, purification of this amino acid from fermentation broth has been of great commercial importance. The present work investigates the reactive extraction and stripping of L-phenylalanine from the aqueous alkaline solution. A quaternary ammonium salt, trioctyl-methyl-ammonium chloride (Aliquat 336) is used as the carrier and potassium chloride salt is used as the stripping agent. In the equilibrium study, the partition coefficient and equilibrium constant are determined at different temperatures (13, 23, 32°C) with different concentration levels of phenylalanine (5, 10, 25, 50 mM) and carrier (50, 100, 200 mM). The kinetic study on rates of extraction and subsequent stripping of phenylalanine is conducted in a stirred transfer cell. A mass transfer model, formulated on the basis of two-film theory, is used to evaluate the mass transfer coefficients for various systems. The concentration ranges employed for these systems are obtained from sensitivity analysis of the model to the mass transfer parameters. The model predicts adequately the experimental concentration-time profiles under various conditions, such as temperature, diluent, carrier and stripping' agent concentrations. The two-film model is modified to take into account the presence of surfactant in the organic phase. The additional interfacial mass transfer resistance due to surfactant thus calculated is found to vary from 3. 77 to 26.32 min/cm at surfactant concentration levels of 10 to 225 mM. Carrier specificity for phenylalanine in the presence of tryptophan, another amino acid present in the fermentation broth on production of phenylalanine, is investigated. Effects of total amino acid loading, temperature, diluent aromaticity and, tryptophan and carrier concentrations are studied. Results show that the carrier employed is more selective towards tryptophan. As a final point, part of the work involved in this thesis has been published in literature or presented at conferences. A list of the publications is given in Appendix A.