Process for the preparation of para-xylene from an effluent of the paraselective dismutation of toluene by a cristallisation process linked to adsorption in a simulated moving bed

摘要

Prepn. of para-xylene from a toluene charge comprises: (a) a para-selective dismutation stage of toluene in the presence of H2 and a catalyst in a zone giving an effluent contg. benzene, toluene, xylenes enriched in para-xylene, ethylbenzene and aromatics of at least 9C; (b) a distillation stage of xylenes, separating benzene toluene and xylenes, in at least two columns; and (c) a high temp. crystallisation stage, pref. at +10 to -30 degrees C in at least one crystallisation zone producing para-xylene of a high purity and a mother liquor depleted in para-xylene. The mother liquor is contacted in an adsorption zone using a simulated mobile bed with a zeolite adsorbent in the presence of a desorbent (toluene) in conditions such as to give a prim. fraction (depleted in para-xylene and contg. toluene) and a secondary fraction enriched in para-xylene and contg. toluene. At least part of the secondary fraction is recycled to the crystallisation zone after having distilled off the toluene.