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Carsten Sievers
School of Chemical and Biomolecular Engineeering
Georgia Institute of Technology
Thursday, February 7, 2008
102 Chemistry Building
10:00 a.m. - 11:00 a.m.
Abstract
Zeolites play an important role in modern refineries as catalysts for processes like fluid catalytic cracking (FCC).
For many applications, it is necessary to increase the hydrothermal stability of the zeolites by steaming or the incorporation of polyvalent cations, e.g. La3+.
In addition to their effect on the stability of the zeolite, lanthanum cations play a role in the formation of Brønsted acid sites during the preparation of the catalyst.
Lanthanum exchanged faujasite with a high aluminum content (LaX) is a promising catalyst for isobutane/2-butene alkylation. This process provides a mixture of isooctanes, which are ideal gasoline additives due to their high octane number. Currently, HF and H2SO4 are used as alkylation catalysts in industrial alkylation plants. Due to the handling hazards of these catalysts the transition to a solid acid catalyzed process is highly desirable. However, premature catalyst deactivation by formation of carbonaceous deposits has prevented the use of solid alkylation catalysts, so far.
We have investigated the deactivation mechanism of LaX in isobutane/2-butene alkylation in detail. Catalytic experiments were conducted for different times on stream and the spent catalysts were characterized by a variety of physicochemical techniques. Four stages of the catalytic performance were identified:
It was found that catalyst deactivation is caused by a combination of site poisoning and pore mouth plugging. The carbonaceous deposits mainly consist of byclic compounds with alkyl side chains. Based on these results, a suitable regeneration procedure is suggested, which allows for using LaX as catalyst in a continuous process.