Modeling and Simulation of a Simulated Moving Bed for the Separation of p-Xylene

The industrial-scale adsorptive separation of p-xylene from a mixture of C8 aromatics in a four-section simulated moving bed (SMB) unit is analyzed through simulation. In the order to describe the behavior of the SMB unit by means of a mathematical model, two approaches were used:  the true moving bed (TMB) approach and the SMB approach. Both approaches assume a constant selectivity nonstoichiometric Langmuir isotherm, an axial dispersion for the fluid flow, and a linear driving force for the intraparticle mass transfer. The TMB and SMB model predictions of steady-state performance of the SMB unit are very close. Therefore, the TMB model was selected to study the effect of the switching time period, adsorbent deactivation, and mass-transfer resistances on the process performance. The adsorbent deactivation which occurs during its lifetime will influence the SMB performance; to keep the p-xylene purity and acceptable recovery, the switching time should be decreased. The TMB package is a useful tool for fas...