Patent ID: 7928276

Claim:
A process for producing very high purity meta-xylene starting from a hydrocarbon feed containing meta-xylene, ortho-xylene, para-xylene, ethylbenzene and optionally naphthenes and C8 paraffins, said process comprising a concatenation of four steps: 1) in a first step of adsorption, consisting of bringing the feed ( 1 ) into contact, in a simulated moving bed adsorption unit (LM 3 ) with a solid zeolitic adsorbant, said adsorption unit delivering at least two fractions, a first fraction termed the extract ( 4 ), which is rich in meta-xylene with a purity in the range 75% to 99%, and a second fraction termed the raffinate ( 5 ) which is depleted in meta-xylene; 2) a second step comprising distillation of the first fraction ( 4 ) in at least one first column (CD 6 ) to separate out the desorbant ( 8 ) a mixture of meta-xylene ( 10 ) in a purity of 75% to 99%, together with impurities ortho-xylene, para-xylene and ethylbenzene, and in at least one second column (CD 7 ) distilling the second fraction to separate out the desorbant ( 9 ) from a mixture ( 11 ) which is depleted in meta-xylene; 3) a third step, comprising crystallization, in at least one unit (CR 12 ) crystallizing the meta-xylene derived from step 2) at a temperature in the range of −50° C. to −95° C. to obtain on the one hand crystals of meta-xylene soaked in their mother liquor, and on the other hand a mother liquor ( 14 ) part of which is recycled as a mixture with the feed ( 1 ) to the inlet to the simulated moving bed adsorption unit (LM 3 ); and 4) a fourth step comprising washing the crystals derived from step 3), at the end of which meta-xylene ( 13 ) is recovered in a purity of at least 99.5%.