Comparison of mesoporous and microporous solid acid catalysts for highly selective synthesis of thymol by vapor phase isopropylation of m-cresol

Abstract

Isopropylation of m-cresol with isopropyl alcohol (IA) as an alkylating agent has been conducted under vapor phase reaction conditions over mesoporous Zn–Al–MCM-41 catalysts with different n Si/( n Zn + n Al) ratios for highly selective synthesis of thymol. The influence of reaction parameters such as reaction temperature, WHSV, mole ratio of reactants, time-on-stream and recyclability reactions, have also been investigated. With increasing the n Si/( n Zn + n Al) ratios of Zn–Al–MCM-41 catalysts from 75 to 380, conversion of m-cresol and yield as well as selectivity of thymol decrease because the number of Brønsted acid sites in Zn–Al–MCM-41 catalysts are found to decrease almost linearly with increasing ratios of n Si/( n Zn + n Al) from 75 to 380. The conversion of m-cresol and selectivity of thymol in Zn–Al–MCM-41(75) remain constant with each cycling of reaction because of no loss of catalytic activity on the inner side surface of pore walls. Furthermore, these catalytic results are compared with those obtained by using Al–MCM-41(with different n Si/ n Al ratio = 21, 42 and 104), HY, Hβ, HM and H-ZSM-5 zeolites. Based on the comparison of catalytic results, Zn–Al–MCM-41(75) is found to be a highly active and recyclable heterogeneous catalyst for the highly selective synthesis of thymol.