Patent ID: 8030533

Claim:
A process for the combined production of high purity para-xylene HPPX and benzene from a first feed principally comprising xylenes and ethylbenzene, and from a second feed principally comprising toluene, in a facility comprising at least the following: a unit for the selective disproportionation of toluene to benzene and xylenes; a unit for para-xylene crystallization; a SMB unit for simulated moving bed adsorption, comprising at least one chromatographic column containing a plurality of beds of an absorbent having a different selectivity for para-xylene, ethylbenzene, meta-xylene and ortho-xylene, said column using a desorbant; in which: a) during the whole of at least one operational cycle of the process: an adsorption feed comprising at least a fraction of said first feed is separated by simulated moving bed adsorption in said simulated moving bed adsorption unit SMB to produce an extract E* which is rich in para-xylene and at least one raffinate which is depleted in para-xylene and contains ortho-xylene and meta-xylene; said raffinate is distilled to recover a distilled raffinate (R) which is substantially free of desorbant; the extract E* is distilled to recover a distilled extract E, substantially free of desorbant; b) during an initial fraction IF of said operational cycle of the process, high purity para-xylene HPPX is produced comprising substantially all of the distilled extract E, the crystallization unit being, during said initial fraction IF, either stopped or essentially supplied with at least a portion of a C8 disproportionation stream essentially comprising xylenes and more than 50% by weight of para-xylene, derived from effluents from conversion of said second feed in said selective disproportionation unit; c) during a final fraction FF of said operational cycle of the process; said second feed is converted in the unit for selective disproportionation of toluene to benzene and xylenes, to produce benzene and a C8 disproportionation stream essentially comprising xylenes and more than 50% by weight of para-xylene; the largest portion or all or said C8 disproportionation stream is integrated into the adsorption feed; the distilled extract E is divided into a first fraction Ea and a complementary second fraction Eb; the crystallization unit is essentially supplied with Ea to produce higher purity para-xylene PX1 and a mother liquor ML; and the PX1 and said complementary second fraction Eb are mixed to produce high purity para-xylene HPPX.