Selective monochlorination of methane over solid acid and zeolite catalysts

Abstract

Chlorination of methane was studied over amorphous silica-alumina, silicalite as well as H-mordenite, X, Y, NaL and H-ZSM-5 zeolite catalysts. The heterogeneous transformations were carried out in a continuous flow reactor in the 200–425 °C temperature range, under atmospheric pressure (methane to chlorine ratio 4:1, GHSV 600 ml/ g h). Chlorination of methane over zeolites in the 200–300 °C temperature range proceeds without selectivity indicating a radical mechanism. Above 300–350 °C, depending on the nature of zeolite, selective monochlorination takes place indicating the dominance of an ionic mechanism. H-mordenite was found to give the best monochlorination at the lowest temperature (99.2% CH3Cl at 350 °C). The observed selectivity of the investigated zeolites is strongly time limited. All investigated catalysts lose their selectivity after five hours on-stream due to extraction of aluminum from the framework of zeolites by hydrogen chloride. Amorphous silica-alumina above 350 °C also catalyzes ionic chlorination. The chlorination of methane over silicalite proceeds via the nonselective radical pathway at the investigated temperatures.