Selective alkylation of toluene with methanol over pentasil-type catalysts
Loading...
Date
1993
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Para xylene is a valuable aromatic compound, because of the demand for oxidation to form tetraphthalic acid, a feed stock for polyester resin and fibers. A relatively high cost is associated with obtaining it in 99+% purity. Purification of para xylene requires separation from three close boiling C8 aromatics i.e. m-xylene, o-xylene, and ethylbenzene and subsequent isomerization of the remaining ortho and meta xylene isomers to an equilibrium mixture. The removal of ethylbenzene is another source of complication. To study the effect of acid sites in pentasil-type catalyst on the toluene alkylation, and para xylene selectivity, four catalysts with different cations in the frame work were synthesized. These catalyst were synthesized to have a SiO2/M2O3=70, where M is Al, B, Fe, or La. X-ray diffraction patterns of these catalysts indicated that all of these catalysts have a pentalsil-type structure. The results of temperature programmed desorptions (TPD) of ammonia indicate that A1ZSM-5 and FeZSM-5 have three different acid sites, weak, medium and strong. The TPD of ammonia of BZSM5 and LaZSM-5 showed a fourth type acid site. The effect of temperature, residence time, and feed composition on alkylation of toluene with methanol over these catalysts were studied. The A1ZSM-5 produced a xylene composition comparable to the equilibrium composition. Alkylation of toluene with methanol over BZSM-5, FeZSM-5, and LaZSM-5 produce xylene composition different than the equilibrium one. The LaZSM-5 catalyst produced the highest para xylene selectivity. The para xylene composition in the xylene isomers was as high as 92%. The p-xylene isomerization over A1ZSM-5, and LaZSM catalysts, indicate that the minimization of the isomerization reaction is the cause of the high para selectivity. All of the catalysts used in this investigation showed relatively rapid deactivation. The cause of the catalyst deactivation is the coke formation inside of the catalyst pores.
Description
Vita
Major subject: Chemical Engineering
Major subject: Chemical Engineering
Keywords
Major chemical engineering