Benzene alkylation with ethane into ethylbenzene over Pt-containing zeolite bifunctional catalysts

Abstract

Ethylbenzene (EB) is currently produced via acid catalyzed benzene alkylation with ethene, which is a product of highly endothermic and energy intensive processes. The new reaction, which uses ethane for benzene alkylation, instead of ethene, would eliminate the ethene production step, thus, leading to the commercial and environmental benefits in the EB manufacturing. Benzene alkylation with ethane into EB can be achieved using bifunctional zeolite catalysts, which combine ethane dehydrogenation into ethene over metal sites with benzene alkylation by ethene over Brønsted acid sites.

The benzene alkylation with ethane into EB over Pt-containing (1 wt.%) ZSM-5 bifunctional catalyst was investigated at six different temperatures (290, 330, 370, 410, 450 and 490oC). The optimum reaction temperature as well as the effect of temperature on the catalyst performance and reaction pathways were established. Excellent catalyst performance was obtained at 370oC, at which very stable catalyst operation (46 h on stream) is observed and the EB selectivity above 90 mol.% is achieved at benzene conversion of 12.5%, which is very close to the maximum equilibrium conversion of benzene into EB at this temperature (13.6%). The obtained results have shown that the temperature has different effects on the rates of the different reaction steps, leading to the different product distributions at different temperatures. It is established that similar reaction pathways operate in the temperature range of 290-490oC and that the EB formation proceeds via two consecutive reaction steps: (i) ethane dehydrogenation into ethene and hydrogen and (ii) benzene alkylation with ethene. The formations of all byproducts have been discussed and a detailed reaction scheme of benzene alkylation with ethane into EB has been proposed. The optimisation of the catalyst compositions was carried out at 370oC with ZSM-5 catalysts containing 0.01, 0.025, 0.1, 0.5 and 1 wt.% of Pt. The PtH-ZSM-5 catalyst with 0.1 wt.% of Pt was found to be the most promising catalyst as it improves the EB selectivity from 90 to 94 mol.% at 12.5% of benzene conversion. With relatively low Pt loading, this catalyst demonstrates very stable performance during 48 hours on stream.

Date of Award	1 Mar 2009
Original language	English
Awarding Institution	University of Bath
Supervisor	Dmitry Lukyanov (Supervisor) & Sean Rigby (Supervisor)