Dual switch simulated moving bed chromatography: An optimal two‐fraction yielding separation process

Abstract

Conventional Simulated Moving Bed Chromatography (C-SMBC) characterized by a single operating point comprising of the internal flow rates and switching period, yields a single fraction of the extract and raffinate, at cyclic steady state. In the current work, we deal with two-fraction yielding Dual Switch SMBC (DS-SMBC) characterized by two operating points implemented during alternate switches. The higher degrees of freedom in Dual Switch SMBC give it the potential of obtaining a higher average extract purity, for one of its two fractions, compared to conventional SMBC, at a certain minimum feed flow rate and minimum average extract recovery. This becomes possible with a trade-off in the average purity of the other extract fraction of Dual Switch SMBC, without any addition to the conventional SMBC equipment. We solve a multi-objective optimization problem wherein we maximize the average purity of one of the extract fractions of Dual Switch SMBC, with the requirement of certain minimum feed flow rate, minimum average extract recovery and minimum average purity of the non-objective extract fraction. One of the aims of the current work is deduction of the working principle of Dual Switch SMBC, that facilitates superior average extract purity. Next, we analyze the trade-offs due to the said process bounds on the objective i.e. average purity of objective extract fraction of Dual Switch SMBC. This has been done for the two case studies of separation: 1) linear isotherm based separation of fructose-glucose in deionized water on cation exchange resin 2) non-linear isotherm based separation of enantiomers of Tröger’s base in ethanol on microcrystalline cellulose triacetate. The findings from the trade-offs in the multi-objective optimization problem, further corroborate our understanding of the working principle.