Alkylation of phenol derivatives catalyzed by zeolites and zirconia based oxides

Abstract

The heterogeneously catalyzed gas phase alkylation of m-cresol with methanol to 2,3,5-trimethylphenol, a precursor for vitamin E, on acidic zeolites and zirconium oxide-based catalysts was investigated. The influence of different acidic centers and of zeolites with different structure and Si/Al ratio was studied. The highest yield of 2,3,5-trimethylphenol (30 wt%) was obtained for the alkylation of 3,5-dimethylphenol on WO3/t-ZrO2 catalyst. In general, the activity of the catalysts can be enhanced if either reaction temperature or methanol to phenol derivate ratio are increased. However, at high degrees of conversion secondary and tertiary products are preferred. Based on the catalytic data it could be assumed that dimethyl ether is rather a side product than an intermediate in the alkylation of phenol derivatives, as expected from conversion of methanol to higher hydrocarbons (MtO and MtG). Comparing infrared spectroscopic data of pyridine adsorption with catalytic results, it could be concluded that Lewis acidic centers, e.g. on WO3/t-ZrO2, play a dominant role in the alkylation reaction. Zeolites, containing preferentially Bronsted acidic sites, were less active. The activity of the catalysts was independent of the texture properties.