A comparison between simulated moving bed and sequential simulated moving bed system based on multi-objective optimization

Abstract

Simulated Moving Bed (SMB), an adsorptive-based continuous separation technology, suffers consumption of high solvent requirement for high desired purity. Sequential Simulated Moving Bed (SSMB) technology, a modified SMB technique featured by dividing a switching period into 3 sub-steps resulting in different flow patterns to reduce solvent consumption at high purity, has been extensively used for industrial glucose/fructose separation. Performances of 4-column regular SMB and SSMB for glucose/fructose separation were compared based on multi-objective optimization. A total of 5 optimization problems with various configurations were investigated. Corresponding flowrate ratio (m-values), average mass flow and internal concentration profiles were used to interpret the optimization results. It was found that m-values optimized for SMB cannot be directly extended to the design of an SSMB process. For given requirements on purity and recovery, SSMB can be used to efficiently reduce water (solvent) consumption ratio, a major industrial concern. This improvement of SSMB is, however, obtained at the cost of reduced unit throughput, besides its more complicated operation. The reduced water consumption and unit throughput can be attributed to its high utility of external mobile phase and low utility of stationary phase, respectively. Contributions of different m-values to reduced water consumption vary not only with the choice of optimization objectives, but also with the range of objectives. It is therefore required to systematically perform independent optimization during the development of SSMB process.