Gas phase alkylation-liquid phase transalkylation process

摘要

Process for the production of ethylbenzene by alkylation over a silicalite alkylation catalyst with subsequent transalkylation of diethylbenzene with the alkylation catalyst and conditions selected to retard xylene production and also heavies production. Benzene and ethylene are applied to a multi-stage alkylation reaction zone having a plurality of series-connected catalyst beds containing silicalite of a predominantly monoclinic symmetry having a silica/alumina ratio of at least 275. Gas-phase ethylation of benzene is at a flow rate to provide a space velocity of benzene over the catalyst to produce a xylene concentration of about 600 ppm or less of the ethylbenzene content. Periodically the space velocity may be increased to a value which is greater than the space velocity associated with a minimum concentration of diethylbenzene in the alkylation product such that diethylbenzene production is enhanced while minimizing any attendant transalkylation reactions within the alkylation reaction zone. The alkylation reactor output is applied to an intermediate recovery zone for the separation and recovery of ethylbenzene with the recovery of a polyalkylated aromatic component which is supplied along with benzene to a transalkylation reaction zone for disproportionation to provide a reduced diethylbenzene content and an enhanced ethylbenzene content. A specific monoclinic silicalite alkylation catalyst has a silica/alumina ratio of at least 300 and has a crystal size of less than one micron.