Selective Isopropylation of Isobutylbenzene over H-Mordenite in Supercritical CO 2 Medium: Remarkable Enhancement in Cat
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Selective Isopropylation of Isobutylbenzene over H-Mordenite in Supercritical CO2 Medium: Remarkable Enhancement in Catalytic Activity and Selectivity for 4-Isobutylcumene Subhash Chandra Laha Æ Kenichi Komura Æ Yoshihiro Sugi
Received: 5 December 2007 / Accepted: 24 January 2008 / Published online: 20 February 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Remarkable enhancement in the catalytic activity and selectivity for the formation of 4-isobutylcumene (4-IBC) was observed in the isopropylation of isobutylbenzene (IBB) over highly dealuminated H-mordenite in supercritical CO2 (sc-CO2) medium. Thermogravimetric analyses confirm that reduced coking of the catalysts in sc-CO2 medium and stronger acid sites in dealuminated H-mordenite (MOR) are the key factors for superior activity and selectivity for 4-IBC. Keywords Supercritical CO2 Dealuminated H-mordenite Isobutylbenzene 4-Isobutylcumene
1 Introduction The Friedel-Crafts alkylation of aromatics catalyzed by solid acids such as zeolites is of significant industrial and pharmaceutical interests [1–3]. Selective liquid-phase isopropylation of isobutylbenzene (IBB) to 3- and 4isobutylcumene (IBCs) derivatives over H-beta (BEA) zeolite has been reported recently [4]. 3-and 4-IBCs are important precursors for the synthesis of antioxidants, pharmaceuticals, fragrances, fine chemicals, etc. [5–7]. The results obtained under conventional liquid-phase reaction conditions; however, showed low conversion of isobutylbenzene (*21 mol%) and moderate selectivity for more relevant 4-IBC (*47 mol%), and the coke amount of the used catalyst was found to be as high as 20 wt.% [8].
S. C. Laha K. Komura Y. Sugi (&) Faculty of Engineering, Department of Materials Science and Technology, Gifu University, Gifu 501-1193, Japan e-mail: [email protected]
In general, all solid acid catalysts, for instance, zeolites with confined micropores, suffer a major set back for its typical deactivation due to coke-formation on the active sites of the catalysts [9, 10]. One of the most important challenges for green catalytic processes is, therefore, to control the diffusion of the reactant(s) and product(s) from active sites to minimize the on-site coke-formation due subsequent acid-catalyzed transformations. Supercritical fluids, such as supercritical CO2 (sc-CO2), are becoming more attractive media for carrying out chemical reactions, since they offer enhanced solubility of reactants and products which can be tuned by variation of pressure and temperature, faster heat transfer from catalysts to dense gases, and easier product separation into reaction step [11–13]. Moreover, due to high density and low viscosity of sc-CO2, an increased solubility of higher molecular weight carbon-rich compounds like polyaromatic hydrocarbons could be achieved under the reaction conditions (minimize the catalyst deactivation), establishing it as an inevitable choice for specified type of chemical reactions [14–18]. In this paper, we report, for the first time, the isopropylation of i
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