Alkylation of m-cresol with methanol and 2-propanol over calcined magnesium-aluminium hydrotalcites

Abstract

Magnesium-aluminium hydrotalcites (MgAl-HTs) with Mg/Al atomic ratio 2,3 and 4 were synthesized by the coprecipitation method. Vapour phase alkylation of m-cresol with methanol was carried out over these samples calcined at 723K in the temperature range 523-723K at atmospheric pressure. A mixture of O- and C- alkylated products, namely, 3-methyl anisole (3MA), 2,5- and 2,3-dimethylphenols (DMP) and 2,3,6-trimethylphenol (2,3,6-TMP) were obtained. The selectivity of these products depends on the m-cresol/methanol feed ratio, temperature and contact times. The catalytic activity of these catalysts are in the order MgAl 3.0-CHT > MgAl 2.0-CHT > MgAl 4.0-CHT. MgAl 3.0-CHT showed ~30% selectivity for 2,5-DMP and 40% selectivity for 2,3,6-TMP with ~40% conversion at 623K or ~70% conversion at 723K. The alkylation of m-cresol with 2-propanol over MgAl 3.0-CHT at 673K offered nearly 80% selectivity towards thymol with nearly 40% m-cresol conversion.