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

摘要

To continuously produce and separate high purity p-xylene from a C.sub. 8 aromatic hydrocarbon charge, successive use is made in combination of (1) a stage of separating low-purity p-xylene (75 to 98%) by simulated moving bed adsorption chromatography, with a ratio for the solvent to charge flow rates of 1.2 to 2.5; (2) a stage of purifying and washing the low-purity p-xylene by recrystallization (-25° to +10° C.); (3) a stage of catalytic isomerization of the charge which has been p- xylene-depleted by the separating stage (1); and recovering an isomerate which is then recycled to the charge. The solvent for desorption in stage (1) and washing in stage (2) is advantageously toluene.