Ethylation of toluene with ethanol using modified HZSM-5 catalysts

Abstract

p-Ethyltoluene (p-ET) is an important precursor to produce poly(p-methylstyrene) (PPMS), a polymer which can be substituted to polystyrene. p-ET is usually produced via ethylation of toluene with ethylene or ethanol, but the use of ethanol as an alkylating agent gains more attention because ethanol can derive from renewable resources. The use of PPMS instead of PS would provide advantages of utilizing toluene to replace benzene which is somewhat more value at present. In this work, the selective formation of p-ET in the ethylation of toluene with ethanol was studied. The effects of SiO₂/Al₂O₃ molar ratios and reaction conditions on p-ET selectivity were studied over unmodified HZSM-5 zeolites. To eliminate the undesired reactions at the external surface of the catalysts, a suitable parent HZSM-5 zeolite was modified by silylation via chemical liquid deposition (CLD) for which tetraethyl orthosilicate (TEOS) was used as a silylating agent. Catalytic activity testing was carried out at 300ºC to 500ºC, toluene to ethanol molar ratios of 1-5, and WHSV of 5-20 ¯¹, using a continuous flow fixed-bed reactor. The HZSM-5 with SiO₂Al₂O₃ molar ratio of 280 was observed to be most suitable in terms of selectivity to p-ET and the optimum reaction condition was at 350ºC, WHSV 20 h¯¹, and toluene to ethanol molar ratio of 3. Moreover the HZSM-5 modified via CLD provided significantly higher p-ET selectivity as compared to the unmodified one. The cycle of CLD treatment played a role in improving the p-ET selectivity but toluene conversion.