Alkylation of xylenes with isopropyl alcohol over acidic clay supported catalysts: efficacy of 20% w/w Cs_2.5H_0.5PW₁₂O₄₀/K-10 clay

Abstract

The alkylation of xylenes with propylene or isopropyl alcohol (IPA) over solid acid catalysts results in the formation of isopropyl xylenes (dimethyl cumenes). However, the use of propylene as an alkylating agent at very high temperatures leads to coke formation, which results in deactivation of the catalyst. The present work covers evaluation of acidic clay-supported catalysts and sulfated zirconia. A variety of solid acid catalysts such as K-10 clay, sulfated zirconia, Filtrol-24, 20% w/w dodecatungstophosphoric acid (H₄₀ PW₃O₄₀, DTP) supported on K-10 clay, and 20% w/w cesium-substituted dodecatungstophosphoric acid (Cs_2.5H_0.5PW₁₂O₄₀, Cs-DTP) supported on K-10 clay under much milder conditions. The best catalyst to achieve maximum conversion and selectivity was determined to be 20% w/w Cs-DTP/K-10 clay. The reactions were conducted in the liquid phase at relatively low reaction temperatures (160−190 °C). The reaction was performed without using any solvent, and the process subscribes to the principles of green chemistry. The catalytic activity has the following order: 20% w/w Cs-DTP/K-10 clay (most active) > 20% w/w DTP/K-10 clay > Filtrol-24 > sulfated zirconia > K-10 clay (least active). The desired product could be efficiently obtained, with selectivities up to 95% at an isopropanol conversion of 98% after 2 h over 20% w/w Cs-DTP/K-10 clay. This process can be a replacement for the existing processes that are based on zeolites, where high temperature and pressure are required. A systematic investigation of the effects of various operating parameters was accomplished and a mathematical model is developed to describe the reaction pathway and validated against experimental results. An overall second-order kinetic equation was used to fit the data, under the assumption that all the species are weakly adsorbed on the catalytic sites.