Controlling the product selectivity in the conversion of methanol to the feedstock for phenol production

Abstract

This work investigated a novel nonpetroleum-based catalytic process of methanol to phenol. The idea was to convert methanol to produce a main product stream having a molar ratio of propylene to benzene/toluene of unity along with relatively higher-value products including para-xylene and alkenes. Such a product mix would be ideal for the manufacturing of phenol. This was achieved using a catalyst of 1.5 wt% zinc impregnated on a silica-deposited HZSM-5 zeolite at 0.1 MPa, 430 °C and 1.2 h⁻¹ weight hourly space velocity. HZSM-5, with its acidic sites predominately being Brønsted acid, produced mainly alkanes and aromatics, of which a good fraction was undesirable nine- or more-nine-carbon higher aromatics. Silica deposition on HZSM-5 passivated the catalytic activity outside the HZSM-5 pores, resulting in an increase of alkenes selectivity, a sharp decrease of nine- or more-nine-carbon higher aromatics selectivity, and a shift of the xylene product from an equilibrium mixture of meta-xylene, para-xylene, and ortho-xylene to mostly para-xylene. Impregnation of 1.5 wt% zinc on silica-deposited HZSM-5 generated more Lewis acid sites and further increased alkene selectivity, which, with the proper selection of process conditions, led to the production of the target stream. A detailed analysis of the effects of silica deposition, zinc impregnation, acidic sites, and process conditions on the catalyst performance was presented.