Simulated moving bed adsorption-desorption process for paraxylene

Abstract

Simulated moving bed processes for the separation of C.sub.8 aromatic isomers using molecular sieve adsorbents are improved by the use of meta-diisopropylbenzene as the eluting agent. The invention describes a process for continuously separating, in a liquid phase, components of the feed mixture by contacting said feed mixture with a solid sorbent and utilizing a simulated countercurrent flow system wherein a liquid stream flows through serially and circularly interconnected desorption, rectification and sorption zones. In such a process the flow of liquid stream is interrupted between both the desorption and rectification zones and a first portion of effluent from the desorption zone, a portion being rich in sorbate may be directly circulated and a second portion, the same comprising sorbate of high purity and desorbent may be fed to a distillation apparatus from which one portion of the sorbate distillate may be circulated as reflux to the rectification zone to maximize the sorbate product purity at reduced costs and another portion is recovered as product. The present improved process is conducted using meta-diisopropylbenzene as a desorbent either alone or in combination with inert diluents such as paraffins. This embodiment provides a more effective separation of paraxylene and ethylbenzene peaks, thus increasing paraxylene recovery and at the same time reducing the amount of recycle and further ethylbenzene-paraxylene separations such as distillations and the like. This better separation allows more efficient use of the adsorbent bed and/or lower ratios of eluting materials to C.sub.8 aromatic feed which results in a more economic process.