Flow and mass transfer for the adsorption separation of para-xylene in a packed bed by particle-resolved CFD simulations

Abstract

As the leading polyester product chain, para-xylene (PX) is the most important xylene isomer. In industry, high purity paraxylene is mainly produced by adsorption separation technology. In this study, the PX adsorption process has been investigated by a 3D particle-resolved CFD model. For spherical particle packed beds, the channeling effect, flow stagnation and backflow regions are the main factors leading to non-ideal flow. According to the residence time distribution (RTD) and adsorbent efficiency, the more uniform the flow in the packed bed, the higher the adsorption separation efficiency. Therefore, low feed flow rate and large bed-to-particle diameter ratio (N) are beneficial to the adsorption process. In addition, the effect of particle geometries (trilobe, five-lobe, Raschig ring, four-spoke ring, and six-hole cylindrical) on the flow and adsorption characteristics of the packed bed has been investigated in terms of pressure drop, adsorbed amount and adsorbent efficiency. Internal void particles perpendicular to the flow direction are unfavorable for the adsorption process. The four-spoke ring adsorbent with more surface areas has the largest bed adsorbed amount and exhibits the best adsorption performance. The trilobe adsorbent has the largest adsorbed amount per unit bed pressure drop and is the optimally shaped adsorbent for industrial PX adsorption separation.