Co-production of para-, meta- and/or orthoxylene, e.g. to obtain pure paraxylene, from a charge containing xylenes, ethylbenzene and 9- 10C hydrocarbons,

摘要

Co-production of para-xylene, meta-xylene and/or orthoxylene uses a chromatographic column initially to separate off and extract para-xylene and a raffinate containing a mixture of meta- and orthoxylenes which may be separated by crystallisation. Co-production of para-xylene, meta-xylene and/or ortho-xylene comprises an initial passage of the charge to a distillation column from which a mixture comprising most of the meta- and para-xylene, ethylbenzene and part of the ortho-xylene is withdrawn at the head, and from the base, a mixture of 9- 10C hydrocarbons and remaining orthoxylene, followed by a separation of the mixture from the head in a simulated mobile bed in a chromatographic column containing several interconnected adsorbent beds in a closed loop with differing selectivities for the xylene and ethylbenzene. The column comprises at least 5 zones defined by injection of the distilled mixture and a desorbent and withdrawals of an extract, containing para-xylene, and intermediate fraction containing ethylbenzene and a raffinate containing ortho and meta-xylenes. A zone 1 comprises the desorption of para-xylene, a zone 2 defining the desorption of ethylbenzene, ortho and meta-xylenes, a zone 3A of adsorption of paraxylene and a zone 3B of adsorption of ethylbenezene. Zone 4 comprises the withdrawal of the raffinate. The raffinate is distilled to eliminate the desorbent and withdraw a distilled raffinate and the extract is distilled to recover a fraction enriched in para-xylene. The process is characterized in that the distilled raffinate is conveyed to a crystallisation zone where meta-xylene is recovered with a purity of at least 99 % or the distilled raffinate is conveyed to a second distillation zone to recover a head flow containing meta-xylene which may be crystallized to 99 % and a base fraction from which orthoxylene can be crystallized to 98.5 %