Scaling Rules and Increasing Feed Rates in Two-Zone and Four-Zone Simulated Moving Bed Systems

Abstract

The scaling rules for chromatographic and adsorption columns and for standard four-zone simulated moving beds (SMBs) are extended to two-zone SMB systems with linear and nonlinear isotherms. Once an old or base design is available, the operational parameters can be predicted by simple algebraic equations. The scaling rules are applied to use the entire available pressure drop in four-zone, two-zone, and parallel two-zone SMB systems. Adding booster pumps between columns to operate columns at their pressure limits and the simultaneous reduction of the particle diameter allows for higher productivity designs with constant product purities and a constant desorbent-to-feed ratio (D/F). The feed rate of a four-zone SMB with one column per zone can be increased by approximately 69% with four pumps between the columns for both linear and nonlinear isotherms compared to the base case with one pump. For systems with one column per zone, the productivities of two-zone and parallel two-zone SMB systems are from 16% to 32% higher than the corresponding four-zone SMBs (with two or four pumps between columns) with constant product purities, a constant D/F, and maximum pressure drop for both linear and nonlinear isotherms. Four-zone SMBs with multiple columns per zone can also be scaled to fully use the available pressure drop and greatly increase productivity with constant product purities. Simulations done with Aspen Chromatography showed that the scaling rules are effective in predicting operating conditions to increase productivity with the same product purities. Operating the high productivity systems at reduced feed rates increases product purities.