Process and apparatus for the separation of p-xylene in C.sub.8 aromatic hydrocarbons with a simulated moving bed adsorption and a crystallization

A process for the separation and recovery of p-xylene contained in a hydrocarbon charge containing C.sub.8 aromatic hydrocarbons, comprising:

• a) continuously contacting in at least one simulated moving bed adsorption zone, a charge containing m-xylene, p-xylene, ethyl benzene and optionally o-xylene with a zeolitic adsorbent bed in the presence of a desorption solvent, under adsorption conditions such that a first fraction is obtained containing the solvent, m-xylene, ethyl benzene and optionally o-xylene and a second fraction is obtained containing the solvent and essentially p-xylene with a purity between 75 and 98% and with an improved productivity;
• b) distilling the first fraction to separate the desorption solvent from a mixture of m-xylene, ethyl benzene and optionally o-xylene;
• c) isomerizing the mixture in an isomerization zone to provide an isomerate, and recycling said isomerate to stage a);
• d) distilling the second fraction and recovering the solvent and p-xylene with a purity of 75 to 98%;
• e) crystallizing the p-xylene of stage d) in a crystallization zone at a temperature between +10.degree. C. and -25.degree. C. to obtain a mother liquor, which is recycled to stage a), and mother liquor-impregnated p-xylene crystals;
• f) washing the p-xylene crystals in a washing zone with a washing solvent and recovering p-xylene crystals with a very high purity level.