| 摘要 |
A catalyst particularly applicable for the selective production of para dialkyl substituted benzenes is provided comprising a porous crystalline aluminosilicate zeolite which has undergone modification by deposition thereon of a coating of silica extensively covering, and residing substantially exclusively on the external surface thereof as a result of contact with a silicone compound of a molecular size incapable of entering the pores of the zeolite and subsequent heating in an oxygen-containing atmosphere to a temperature in excess of 300.degree.C. but below a temperature at which crystallinity of the zeolite is adversely affected at a rate such that the silicone compound does not volatilize prior to undergoing oxidation to silica. The zeolite is characterized by an activity, in terms of alpha value, of between about 2 and about 5000, a xylene sorption capacity greater than 1 gram/100 grams of zeolite and an ortho-xylene sorption time of 30 percent of said capacity of greater than 10 minutes, said sorption capacity and sorption time being measured at 120.degree.C. and a xylene pressure of 4.5 ? 0.8 mm. of mercury. There is also provided a process for the selective production of para dialkyl substituted benzenes containing alkyl groups of 1 to 4 carbon atoms, typified by para-xylene, by contacting, under conversion conditions, a hydrocarbon precursor selected from the group consisting of mono alkyl-sub-stituted benzes having 1-4 carbon atoms in the alkyl substituent, e.g. toluene, ethyl benzene, propyl benzene or butyl benzene and a mixture of said precursor or benzene with an alkylating agent containing from 1 to 4 carbon atoms with the above catalyst and recovering from the resulting product mixture, a para dialkyl substituted benzene in an amount greater than the thermodynamic equilibrium concentration thereof in the total dialkyl substituted benzenes produced. |
