Model development and simulation of lysine ion exchange in single and multicolumn systems

This research addresses equilibrium and mass transfer phenomena in the adsorption of L-lysine on cation exchange resins and the development of models to describe single and multicolumn processes for L-lysine recovery from fermentation broths. L-lysine can exist in divalent and monovalent cationic forms, in zwitterionic form, or in monovalent anion form. The cationic forms are retained by a cation exchange resin, while anionic and non-ionic contaminants are unretained. Since divalent and monovalent forms partition differently between the solution phase and the resin phase and exhibit large differences in resin-phase diffusivity, the reversible interconversion of these forms has to be taken into account to describe equilibrium and ion exchange kinetics. L-lysine recovery from the resin is typically carried out with ammonia, which increases the pH converting L-lysine to its anionic form, while providing the ammonium counterion for the exchange process. As result, the interactions of L-lysine, ammonia, and other cationic impurities that may be present also need to be addressed. Finally, industrially, multicolumn systems are typically used to improve productivity and reduce desorbent consumption. Thus, a model capable of describing multicolumn operation is needed. A systematic approach was used to address these issues by developing the requisite fundamental understanding of equilibrium and transport phenomena and establishing mathematical tools for their description. This approach has resulted in: (1) a model describing the equilibrium and transport of L-lysine in a cation exchange resin; (2) a model describing L-lysine adsorption and desorption in batch and single column processes; and (3) a dynamic model predicting the multicolumn system behavior. Predictions based on these models are successfully compared with experimental results thereby providing a basis for using these models in process design and optimization.