Patent ID: 6841714

Claim:
Process for co-production of paraxylene and metaxylene and/or orthoxylene from a feedstock that contains xylenes, ethylbenzene and C9-C10 hydrocarbons, whereby the process successively comprises: A passage of feedstock ( 1 ) in a column ( 2 ) for distillation of xylenes from where a mixture ( 3 ) that comprises the majority of metaxylene, paraxylene, ethylbenzene and at least a portion of orthoxylene is drawn off at the top, and from where a flow ( 4 ) of C9-C10 hydrocarbons and the remaining portion of orthoxylene is drawn off at the bottom; A separation of top mixture ( 3 ) in a simulated moving bed in at least one chromatographic column ( 9 ) containing a number of beds of an adsorbent that are interconnected in a closed loop and having a different selectivity for paraxylene, ethylbenzene, metaxylene and orthoxylene, whereby said column comprises at least five zones that are delimited by injections of mixture ( 3 ) (adsorption feedstock) and a desorbent ( 8 ) and draw-offs of an extract ( 10 ) that contains paraxylene, an intermediate fraction ( 11 ) that contains ethylbenzene, a raffinate (R 2 ) ( 12 ) that contains orthoxylene and metaxylene, whereby a paraxylene desorption zone 1 is included between the injection of the desorbent and the sampling of the extract, whereby a zone 2 for desorption of ethylbenzene, orthoxylene and metaxylene is included between the sampling of the extract and the injection of the adsorption feedstock, whereby a zone 3 A for paraxylene adsorption is included between the injection of the feedstock and the draw-off of the intermediate fraction, whereby a zone 3 B for ethylbenzene adsorption is included between the draw-off of the intermediate fraction and the draw-off of raffinate (R 2 ), and whereby a zone 4 is included between the draw-off of raffinate (R 2 ) and the injection of desorbent, whereby the process is characterized in that Raffinate ( 2 ) is distilled to eliminate essentially all of the desorbent, and a distilled raffinate ( 18 ) is drawn off, The extract is distilled to recover a paraxylene-enriched fraction ( 16 ). The process is also characterized in that: Either distilled raffinate ( 18 ) is sent at least in part to at least one crystallization zone ( 27 ), and metaxylene with a purity of at least 99% is recovered, Or distilled raffinate ( 18 ) is sent at least in part into a second distillation zone ( 23 ), a top flow ( 24 ) that contains metaxylene and a bottom fraction ( 25 ) that contains orthoxylene ( 24 ) are recovered, the top flow is crystallized at least in part, metaxylene with a purity of at least 99% is recovered, and/or said bottom fraction is crystallized at least in part, and orthoxylene with a purity of at least 98.5% is recovered.