Two-Zone SMB Process for Binary Separation

Abstract

Two-zone simulated moving bed (SMB) systems with a storage tank were developed for binary separation. Simulations were done with Aspen Chromatography for the linear dextran T6−raffinose mixture and the nonlinear binaphthol enantiomers mixture. The results for these linear isotherms show that two-zone SMBs give purities comparable to those obtained for a four-zone SMB with the same productivity and desorbent-to-feed ratio (D/F). At D/F = 2.794, the purities obtained in a two-zone decoupled SMB for dextran T6 and raffinose are 94.5% and 97.6%, respectively, whereas in a two-zone coupled SMB, the purities are 95.0% and 97.5%, respectively, compared to a four-zone SMB's purities of 96.1% and 96.6%, respectively. The results for the nonlinear isotherms show that these two-zone SMB systems can obtain good separation but with more desorbent than required for a four-zone SMB. Simulations for two-zone SMBs with one column per zone show that partial feed can improve the product purities and recoveries considerably, particularly at the optimum feed length. Early feed introduction increases the raffinose purity, whereas late feed introduction increases the dextran T6 purity. Partial-feed operation shows very modest improvement in raffinate purity for the binaphthol enantiomers system. The results for two-zone SMBs with multiple columns per zone show that adding more columns per zone is not always beneficial for separation in two-zone SMBs for both linear and nonlinear isotherms.