Dual bed xylene isomerization

The process according to claim 18 wherein the silica bound intermediate pore size zeolite is modified by a selectivation sequence comprising the additional steps of

• (d) contacting the calcined extrudate of step (c) of claim 19 with a liquid comprising a liquid carrier and at least one organosilicon selectivating agent having at least two silicon atoms per molecule under conditions sufficient to incorporate said organosilicon selectivating agent in the extrudate,
• (e) calcining the extrudate of step (d) under conditions sufficient to decompose said organosilicon selectivating agent and to remove any residue of said liquid carrier from said extrudate;
• and, optionally,
• (f) repeating selectivation steps (d) and (e) at least once.

A process for isomerizing a feed which contains an aromatic C.sub.8 mixture of ethylbenzene and xylene in which the para-xylene concentration is less than that at thermal equilibrium, which process comprises contacting the feed, under isomerization conditions, with a two component catalyst system including a first catalyst and a second catalyst located in separate catalyst beds

• wherein
• the first catalyst comprises ZSM-5 which has been modified by being exposed to at least one selectivation sequence, wherein the selectivation sequence includes the steps of contacting the ZSM-5 with a selectivating agent in a carrier and subsequently calcining the selectivated ZSM-5, said ZSM-5 comprising a medium or large crystal size zeolite, said ZSM-5 being silica bound, said first catalyst comprising a hydrogenation component;
• and
• the second catalyst comprises a small crystal size ZSM-5, and wherein the ZSM-5 has an alpha value of less than about 150, said second catalyst comprising a hydrogenation component;
• whereby at least 30% of the ethylbenzene present in the aromatic C.sub.8 mixture is converted to benzene, xylene, or to compounds readily removed by distillation from the aromatic C.sub.8 mixture.