(50b) Disproportionation of Toluene And Transalkylation of Tri-Methylbenzene Over Different Zeolites

Toluene, xylene and benzene, derive from benzene alkylation, mainly are produced from catalytic reforming and gasoline pyrolysis. Benzene is a key raw material for many intermediates of petrochemicals, and xylenes are important starting materials for the production of synthetic fibers, plasticizers, and resin. Statistics at 1999 indicate that production capacity ratio of three chemicals is 32:36:32. However the world industrial demanding for three chemicals is 34:11:55. Production capacity of three chemicals can not meet the demanding [1]. Toluene is superfluous and benzene is scant. Moreover the demanding for benzene and xylene is increasing at the rate of 10% per year, and the demanding for toluene changes a little. And the price of toluene is much lower than benzene and xylene. So it is advantageous that toluene and trimethylbenzene are convert to xylene and benzene. Disproportionation of toluene and transalkylation of trimethylbenzene is a complicated system including disproportionation, isomerization, transalkylation and dealkylation. The aim is to increase the yield of xylene and conversion of toluene and trimethylbenzene.

Industrial catalysts for disproportionation of toluene and transalkylation of trimethylbenzene mainly use zeolite with medium pore, such as ZSM-5, or one-dimensional zeolite with large pore, such as Mordenite. Both the zeolites have some obvious shortcomings. E.g space velocity is low and molar ratio of xylene and benzene is also low. More recently three-dimensional zeolite with large pore, such as Y and Beta zeolite, are reported to show some advantages [2,3]. So the scaning of zeolites used for disproportionation of toluene and transalkylation of trimethylbenzene is necessary.

In this paper several zeolite are scanned including ZSM-5, Y, Beta, FBZ and FMZ. FBZ and FMZ, two composite zeolites, are first synthesized by our laboratory. FBZ is composed of Y zeolite and Beta zeolite. FMZ is composed of Y and ZSM-5 zeolite. The two composite zeolites possess lots of mesopores, distinctly different from pure microporous zeollite. The results indicate that FBZ and FMZ have higher catalytic activity, and Y zeolite more quickly deactivates.

Reference

1. Tseng-Chang Tsai, Shang-Bin Liu, Ikai Wang, Applied Catalysis A: General 1999, 181: 355-398.

2. Das, J., Bhat, Y.S., Halgeri, A.B., Catal. Lett., 1994, 23: 161-168.

3. Aneke, L.E., Gemtsen, L.A., Eilers, J., Tnon, R., J. Catal., 1979, 59: 37-44.