New flow rate strategies for simulated moving bed systems
Abstract
The work in this thesis develops a series of operational strategies based on variable flow rates for Simulated Moving Bed (SMB) separation systems using Aspen Chromatography simulation software and Matlab and VBA programs. The standard operation for SMB uses constant, continuous flow rates. The essence of the inventions is to break the traditional flow style into variable, discontinuous flows. “Partial feed” divides each switch step into three subintervals and feeds the SMB only during the middle subinterval. This operation improves the separation efficiency of both 4-zone and 3-zone SMBs with one column per zone for fractionation of Dextran T6 and Raffinose, which have linear isotherms. For a four-zone SMB with one column per zone, constant productivity and constant desorbent consumption, the average product purity is increased from 92.45% with standard operation to 95.34% with a partial feed operation, and the average recovery is increased from 91.87% to 94.80%. If the product purities are held constant, the productivity is increased by 70% and the desorbent to feed ratio (D/F) is reduced by 58.8% with partial feed operation. For a three-zone SMB with one column per zone, the product purity is increased about the same amount with constant productivity and D/F value (from 95.75% to 98.81%). By combining partial feed with selective withdrawal, which recycles the part of the raffinate product which is pure desorbent, the D/F value decreases from 5.6 to 2.5 with almost no change in product purities. It is slightly better than the separation in a traditional four-zone SMB with two columns per zone with the same productivity and the amount of adsorbent. Variable flow rate operation generalizes partial feed operation—all the internal and external flows operate with three stepwise flow rates within each step. For a four-zone SMB with one column per zone separating a linear system the extract purity increased from 85.3% to 91.4% and raffinate increased from 89.2% to 94.9%. For a nonlinear system, the extract product purity increased from 85.0% to 94.1% while the raffinate purity increased from 84.9% to 90.3%.
Degree
Ph.D.
Advisors
Wankat, Purdue University.
Subject Area
Chemical engineering
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