(395k) Standing Wave Analysis for 4-Zone SMB with Thermal Gradients

The isothermal simulated moving bed (SMB) for binary separations has been shown to produce high throughput of high purity product. An inherent limitation of this process is its high desorbent consumption, which leads to high energy consumption in the separation device that recovers desorbent. In order to overcome this limitation, temperature swing adsorption (TSA) or thermal gradient have been integrated with the SMB process (thermal SMB)^1-3. The thermal gradient process is operated at high temperature for adsorbent regeneration, and at cold temperature for desorbent regeneration. This results in a lower desorbent to feed (D/F) flow rate ratio and subsequently reduces energy consumption in the entire system. The optimal design of thermal SMB processes is considered a major challenge because the current initial design method (local equilibrium theory) only provides a region of acceptable design parameters, thus, requiring many simulation trials.  In this study, Standing Wave Analysis (SWA), developed originally for 4-zone isothermal SMB fractionators, is extended to SMB systems with thermal gradients, and then is used to locate the optimal operating conditions for a 4-zone thermal SMB fractionation. The accuracy of SWA was validated by Aspen Chromatography simulations for toluene/p-xylene separation with silica gel as the adsorbent and n-heptane as the desorbent with two columns per zone.  The system was operated in the temperature range of 0–80^oC and it was shown that SWA provides very good prediction of optimal operating conditions.

References

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