A new process for the production of xylenes and para-xylene for the synthesis of terephthalic acid

摘要

The process achieves a high yield of high purity para-xylene from an initial reformate which contains ethylbenzene and xylenes. A catalytically reformed hydrocarbon charge is subjected to a distillation to produce a mixture of 8C aromatic isomers in which: (a) the mixture is distilled (11) to give a fraction A enriched in ethylbenzene containing metaxylene and paraxylene, and a fraction B containing para-, meta- and ortho-xylene and C9+ aromatics; (b) the fraction A is hydrogenated (23) in a hydrogenating zone; (c) the hydrogenated fraction is isomerized (24) in hydroisomerizing conditions; (d) the isomerate is distilled (26) to produce a distillate (27) containing 1,3- and 1,4-dimethylcyclo-hexane and a residue containing 1,2-dimethylcyclohexane and ethylcyclohexane; (e) the distillate is recycled to the catalytic reforming zone (2); and (f) the residue is recycled to the hydrogenation/isomerization zone. The fraction B is treated as follows:- -the fraction is separated by distillation (14) to produce a distillate C containing ortho-, meta- and para-xylenes, and a residue D containing heavy hydrocarbons; -the distillate C is separated in an adsorption zone (17) comprising a mobile bed, in the presence of a desorbent, into a fractions depleted and enriched in para-xylene; -the depleted fraction is isomerized (20) in liquid phase conditions in the presence of toluene to nullify dismutation of the xylenes; and -the para-xylene rich fraction is distilled to eliminate desorbent and pure para-xylene recovered.