Process for separation of C8 aromatic compounds with limited recycling

摘要

Process for the production of paraxylene from a C8 aromatic feedstock that comprises the following stages:
A stage for separation by adsorption in a simulated moving bed SMB that produces an extract that contains at least 95% paraxylene and at least one raffinate R that contains ethylbenzene,A recycling of raffinate to the SMB separation stage after isomerization, in which R is separated in membrane separation means to obtain a first fraction F1 that is relatively high in ethylbenzene, which is purged, and an additional fraction F2 that is relatively low in ethylbenzene, which is recycled to the SMB after a single isomerization, preferably in the liquid phase.

主权项

1. A process for producing paraxylene from an aromatic hydrocarbon feedstock containing xylenes and ethylbenzene, said process comprising:
introducing said aromatic hydrocarbon feedstock and a desorbent into an adsorption separation stage having a simulated moving bed, and removing from said adsorption separation stage an extract E, at least one raffinate R comprising ethylbenzene, and another raffinate R* having an ethylbenzene content which is less than that of R; distilling said extract E to obtain product paraxylene comprising at least 95% paraxylene and desorbent; distilling said at least one raffinate R comprising ethylbenzene to obtain a first distilled raffinate and desorbent; distilling said another raffinate R* having an ethylbenzene content which is less than that of R to obtain a second distilled raffinate and desorbent; introducing at least part of said first distilled raffinate into a membrane separation stage, wherein said at least part of said distilled raffinate is separated by membrane separation through a zeolitic-type membrane selective for ethylbenzene relative to orthoxylene and to metaxylene, to produce a first fraction F1 enriched in ethylbenzene and at least one additional fraction F2 which is depleted in ethylbenzene; combining said at least one additional fraction F2 depleted in ethylbenzene and said second distilled raffinate to form a mixture; introducing said mixture of at least one additional fraction F2 depleted in ethylbenzene said second distilled raffinate into a single liquid phase isomerization stage operating at a temperature of between 200° C. and 260° C., a pressure of between 2 MPa and 3 MPa, and an hourly volumetric flow rate encompassed between 2 h−1 and 4 h−1 to produce an isomerate; recycling said isomerate to said aromatic hydrocarbon feedstock at a point upstream of said adsorption separation stage having a simulated moving bed, and subjecting at least a portion of said first fraction F1 enriched in ethylbenzene to dehydrogenation.