Mesoporous molecular sieves: alkylation of anisole using tert-butylalcohol
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Catalysis Letters Vol. 110, Nos. 1–2, August 2006 (Ó 2006) DOI: 10.1007/s10562-006-0084-0
Mesoporous molecular sieves: alkylation of anisole using tert-butylalcohol P. Kamalaa and A. Panduranganb,* a Department of Chemistry, Anna University, Chennai 600025, India CAER & Center for Nanoscalescience and Engineering, University of Kentucky, Lexington KY, 40506-0046, USA
b
Received 15 March 2006; accepted 23 May 2006
Mesoporous aluninosilicate Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 and 100 have been synthesized under hydrothermal condition and these materials were characterized by XRD, FTIR, BET and pyridine adsorption techniques. The catalytic performance was examined in the vapor phase tert-butylation of anisole with tert-butanol at the temperatures between 150 and 250 °C under atmospheric pressure. The results indicate that Al-MCM-41 (25) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4DTBA). Maximum conversion of anisole is observed at 175 °C and decreased thereafter with increasing temperature. The influence of molar feed ratio, influence of temperature, WHSV and time on stream on the selectivity of products was investigated and the results are discussed. KEY WORDS: tert-butylation; anisole; Al-MCM-41.
1. Introduction Alkylation of aromatics is an important reaction in organic chemistry widely used in the synthesis of petrochemicals, fine chemicals, pharmaceuticals, fragrances, dyes, and agrochemicals [1]. Conventionally Friedel–Crafts reactions are performed in the liquid phase using homogeneous acid catalysts like AlCl3, BF3, and H2SO4, often lacking selectivity toward the targeted product [2] and the corresponding industrial processes present severe environmental problems [3]. Alkylation reactions over solid acid catalysts have generated a lot of interest as alternatives for the conventional catalysts and are also being employed in several industrial processes [4–6]. The use of solid catalysts such as zeolites [7–10], clays, [11,12], and ion exchange resins [13] for the alkylation of aromatic compounds has been studied. The use of zeolites as solid acid catalysts in various processes of refining, in production of petrochemicals and fine chemicals has grown over the last few decades because of their remarkable shape selectivity, durability and reusability [14,15]. However, the small size of their cages and pore apertures has become a drawback in the treatment of heavy feeds or in the diffusion of large reactant and product molecules. There has been an increasing demand for molecular sieves having pores sizes in the mesopore range in order to treat heavier
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feeds and produce (more bulky) fine chemicals [16–18]. Mesoporous Al-MCM-41 molecular sieves have become catalysts in widespread use in recent years in many reactions of industrial importance. Al-MCM-41 has already been proposed as an alkylati
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