Comparing true countercurrent and Simulated Moving-Bed chromatographic reactors

Simulated Moving Bed reactors (SMBR) combine chemical reaction and adsorptive separation within one single continuous and countercurrent unit. This integration promises substantial improvements in process performance, especially when applied to equilibrium-limited reactions involving such heat-sensitive products as fine chemicals and pharmaceuticals. In this work, the interplay among the relevant process design parameters (dimensionless ratios of the fluid and solid flow rates, and the Damkohler numbers for each section of the unit) is investigated. For this, an analytical solution of differential mass-balance equations for the corresponding true countercurrent process (TCC), using as a model system the reaction A reversible arrow B + C with each species exhibiting linear adsorption behavior, was developed. Based on this solution, criteria were derived for the optimum process design with respect to productivity and solvent consumption. Comparing these results with numerical simulations of an SMBR unit shows that the TCC model does not apply to SMBR units with a finite number of columns per section, that is, units of practical relevance, because the two units exhibit different residence time distributions and, hence, lead to different degrees of conversion.