Effects of Modified Beta Zeolites with Acid on Anisole Acetylation in a Fixed Bed Reactor
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Effects of Modified Beta Zeolites with Acid on Anisole Acetylation in a Fixed Bed Reactor Dishun Zhao Æ Jinlong Wang Æ Juan Zhang
Received: 17 June 2008 / Accepted: 27 July 2008 / Published online: 9 September 2008 Ó Springer Science+Business Media, LLC 2008
Abstract A beta zeolite sample (Si/Al = 30) was modified by citric acid, tartaric acid, and hydrochloric acid. The catalytic performances of these zeolite together with another beta zeolite (Si/Al = 12.5) were tested in the anisole acetylation in a fixed-bed configuration. The zeolites were characterized by powder X-ray diffraction, FTIR of adsorbed pyridine, and temperature programmed desorption of ammonia. The ratios of Si/Al, the specific surface areas, and the pore sizes were also measured. The results showed that the most active and stable behavior was achieved on the HCl treated zeolite. The strong acid sites as many as possible but with an appropriate concentration and strength were needed in order to obtain an optimum activity and stability. Keywords Beta zeolite Modification Anisole Acetylation Fixed bed reactor
1 Introduction Friedel–Crafts acylation of aromatics is one of the most important synthetic reactions for the preparation of aromatic ketones, which are key intermediates in the production of pharmaceuticals, dyes, fragrances, and agrochemicals [1–3]. The conventional methods for D. Zhao (&) J. Wang J. Zhang School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China e-mail: [email protected] D. Zhao College of Chemistry and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China
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production of aromatic ketones involve acid chlorides or anhydrides used as acylated agents and Lewis acids such as AlCl3, BF3 etc. used as catalysts. As a consequence, a number of problems including the need of more than stoichiometric amounts of catalysts with production of a large amounts of inorganic by-products, in particular hydrochloric acid, and the cumbersome work-up steps resulting from the hydrolysis of the mixtures of the products, are effected. Moreover, the Lewis acid catalysts cannot be regenerated [4–8]. In view of the disadvantages of the homogeneous Lewis acid catalysts in current practical aromatics acylation reactions, considerable efforts have been made to develop heterogeneous solid acid catalysts [9–13]. Zeolites, with their unique acid properties and pore structures, exhibit good catalytic activity and selectivity in the acylation of aromatic compounds [3, 14, 15]. However, zeolites as acylation catalysts often suffer from fast deactivation and often need regeneration. The reasons for the catalyst deactivation can be attributed to the dealumination of zeolites by the acidic byproducts and the stable adsorption of heavy products and the permanent deposition of carbonaceous substances on the active sites of the catalysts [16, 17]. Results showed that the stability of zeolites can be improved by increasing the molar ratio of the substrate aromatic ether
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