Isobutane/2-butene alkylation with zeolite Y without Br<FONT FACE=Symbol>Æ</FONT>nsted acidity

Abstract

Foi estudada a alquilação de isobutano com 2-buteno catalisada por zeólitas Y trocadas com cátions metálicos, usando um cloreto de alquila com iniciador de carbocátions. Os resultados indicaram que, comparavelmente a uma zeólita protônica, a desativação foi significativamente mais lenta e a produção de tri-metilpentanos foi maior nas zeólitas trocadas com metais. Os cátions agem como sítios ácidos de Lewis, interagindo com o cloreto e iniciando as reações de carbocátions. Os resultados suportam a hipótese de que os sítios protônicos favorecem a adsorção das olefinas, aumentando a velocidade de oligomerização.Alkylation of isobutane with 2-butene was performed on metal-exchanged Y zeolites, using an alkylchloride as carbocation initiator. The results indicated that, compared with a protonic zeolite, the deactivation was significantly slower and the production of trimethylpentanes was higher on the metal-exchanged zeolites. The metal cations act as Lewis acids, interacting with the chloride initiating the carbocationic reactions. The results also support the view that protonic sites on the catalyst favor adsorption of the olefin, thus increasing oligomerization rate. Keywords: alkylation, zeolite, Br∅nsted acidity, gasoline IntroductionThe alkylation of isobutane with 2-butene is a reaction normally catalyzed by Br∅nsted acids. The primary function of the acid system is to protonate the hydrocarbons to generate small concentrations of carbocations. Nevertheless, as the reaction begins it becomes autocatalytic 1-3 due to a hydride transfer step as shown in Scheme 1. Alkylation has been used since the 1930's to produce high octane gasoline. 4,5 However, due to environmental concerns, it will grow in importance in oil refining in the next years. The alkylate, predominantly with eight carbon atoms, is a valuable blending for the adjustment of the gasoline composition to attain the environmental requirements.3 Alkylation is normally catalyzed by H 2 SO 4 or HF. However, these acid systems present severe environmental problems, especially HF, whose use in new alkylation plants is forbidden in the USA. 6 Today, these acids account for about 30% of the refining catalyst market, but this share tends to increase, as alkylation grows in importance. 3The search for a solid catalyst to replace HF and H 2 SO 4 in alkylation has been a long-standing challenge for chemists.6-8 Many materials are active for alkylation, but they show rapid deactivation, due to oligomerization, 9 impairing the development of a commercial solid catalyst for this process. Some studies tend to overcome this problem, by working on process engineering solutions. 10According to some authors, the rapid deactivation of solid acid catalysts is due to a preferred adsorption of the olefins on the surface. 3,11 This favors successive alkylation reactions, forming the oligomers, which do not desorb from the catalyst surface.Zeolites are among the best solid catalysts tested in alkylation. One of the main features of the zeolites is their ability to catalyze hyd...

New Insights into the Progress on the Isobutane/Butene Alkylation Reaction and Related Processes for High-Quality Fuel Production. A Critical Review

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Intrinsic flexibility of porous materials; theory, modelling and the flexibility window of the EMT zeolite framework

“…Zeolites are most prominently used in the petrochemical industry as catalysts for cracking, alkylation and isomerization (Marcilly, 2003;Degnan, 2003). EMT-type zeolite, EMC-2, for example is an extremely effective industrial catalyst for the alkylation of isobutane with 2-butene (Stocker et al, 1996;Rosenbach & Mota, 2005). A major ambition for the field is the development of 'designer' zeolites with tailored geometry for new catalytic applications, by the appropriate choice of synthesis conditions and organic structure-directing agents (oSDAs) whose shape is intended to template the specific pore geometry of the desired framework (Dhainaut et al, 2013).…”

The tert-butyl cation on zeolite Y: A theoretical and experimental study

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