Ion-exchange in fluidized/expanded beds for recovery of L-phenylalanine

Experimental and theoretical studies were carried out to investigate the performance of a batch, fluidized/expanded bed ion-exchange system. Exchange of scL-phenylalanine on cation exchange resin was studied in columns of 1-4 cm diameter and in the linear velocity range 5-40 cm/min. The breakthrough curves were obtained at various design and operating conditions with changing column size, distributor, feed pH, bed height, flow rate, and number of stages. The breakthrough data were analyzed by two theoretical models. A CSTR-type model which is called a lumped model fitted the data well when bed aspect ratio (bed height/bed diameter) was less than 1.5 and column diameter was 4 cm or less. The fluidized bed was considered a bed that can be well simulated by the lumped model which assumes uniform mixing for the bulk phase, and the expanded bed was considered a bed where the lumped model fails because of reduced backmixing. A packed bed model (VERSE) with axial dispersion, film diffusion, and intraparticle diffusion, fitted the data for both fluidized beds and expanded beds successfully. Experimental and theoretical results showed the bed-type changes from a fluidized bed to an expanded bed as the bed aspect ratio increases. The breakthrough curves for the expanded bed and a packed bed were almost identical except at very short times. When sieve plates were used as liquid distributors, the plate with more holes of a smaller size resulted in better sorption efficiency. Mass transfer at different flow rates and the effects of bed-type and multiple stages are discussed. Intraparticle diffusion models were studied with VERSE simulations and experimental breakthrough data from packed beds. The surface diffusion model was more appropriate for this ion-exchange resin than the pore diffusion model. The parallel diffusion model was successfully used to predict column breakthrough at different conditions (feed concentration, flow rate, column diameter, and bed height) with reasonably consistent diffusivities. Mass transfer parameters in the bulk phase of fluidized/expanded beds were studied with VERSE simulations and experimental breakthrough data. Very large axial dispersion coefficients were needed for small bed aspect ratios, but packed bed correlations were successfully used for large bed aspect ratios. The study showed there is more dispersion in columns with larger diameters or shorter bed heights