Microporous Zeolite based Catalysts for Fine Chemicals

Abstract

Several new zeolite-based catalysts have been developed for chemical processes namely the Friedel Crafts acylation and alkylation, and consecutive oxidative acidic reactions of olefin to diol in which the products from theses reactions are valuable chemicals and intermediates in the pharmaceutical and polymer industries. Most of these zeolite based catalysts have been successfully prepared by using rice husk ash as silica source. Ferrierite (Fer), zeolite Beta with different Si/Al ratios and zeolitic mesoporous ITQ-6, have been obtained in pure form in a shorter crystallization time whereas titanium silicalite (TS-1) and zeolite X were also obtained by using commercial silica and natural zeolite respectively. The synthesized zeolites catalysts are modified in order to suit the named processes. For Friedel Crafts reaction, alkylation of resorcinol and acylation of anisole were carried out. Zeolite Beta in modified form: hydrogen-Beta(H-Beta), niobium-Beta(Nb-Beta), gallium-Beta(Ga-Beta) and ITQ-6 and Nb-ITQ-6 were tested their reactivity in alkylation of resorcinol with tert-butyl alkylation agent to obtain antioxidants 4-tert-butyl resorcinol and 4,6-di-tert-butyl resorcinol as main products. Nb-Beta was found to be the most active catalyst for the reaction with more than 90% conversion and nearly 100% selectivity for the 4,6-di-tert-butyl resorcinol while Ga-Beta gave nearly 100% selectivity for 4-tert-butyl resorcinol. The strength of antioxidant property of the reaction products is 4X higher than the resorcinol. The reactivity of the catalysts for the reaction depends mostly on the strength of Brönsted acidity together with high zeolite crystallinity rather than the mesoporous property of the catalysts. For the acylation of anisole with propionic anhydride catalysed by H-Fer with Si/Al ratio ~6, gave the highest conversion (60%) and 80% selectivity for p-methoxypropiophenone in which slightly lower activity as compared to H-Beta (~ 80% conversion) due to the smaller pore size of H-Fer. In another reaction process, a consecutive oxidative acidic reaction of olefin to diol, bifunctional oxidative acidic TS-1 zeolite catalysts have been developed and was tested on the consecutive transformation of 1-octene to 1,2-octanediol via 1,2-epoxyoctane formation as model reaction. The bifunctional catalysts were prepared by incorporating acidic metal oxides/sulphates on oxidative TS-1: tungsten oxides (WO3/TS-1), niobium oxide (Nb/TS-1), sulfated zirconia (SZ/TS-1) and sulfated acid (SO42-/TS-1) in such a way the location of oxidative sites are inside the pore while the acidic sites located on the external surface of the catalyst. Brönsted acid sites were found in all prepared catalyst except in SO42-/TS-1. All catalysts showed significant increased in the rate of formation of 1,2-epoxyoctane compared to TS-1 alone. Brönsted acid sites from acidic oxides/sulphates was responsible for the formation of 1,2-octanediol, with Nb/TS-1 catalyst gave the highest yield of diol. The higher activity of bifunctional catalysts was due to the location of acidic sites in the immediate vicinity of the oxidative sites which enable the epoxidation product to undergo rapid hydrolysis at acid sites.