Hierarchical mesoporous ZSM-5 for the dehydration of methanol to dimethyl ether

Abstract

Hierarchical mesoporous ZSM-5 zeolites were synthesized using small organic cations of tetrapropylammonium and meso-sized cationic polymers of dimethyldiallyl ammonium chloride acrylamide copolymer as templates. The zeolites were used for the dehydration of methanol to dimethyl ether (DME). Characterization results showed that the basic MFI-type structure was still obtained after adding the cationic polymers, while their nitrogen isotherms exhibited a broad hysteresis loop at relative pressures higher than 0.4, which proved the presence of mesopores. The mesoporosity of the hierarchical mesoporous ZSM-5 can be adjusted simply by adding different amounts of the cationic polymer. Catalytic tests showed that the hierarchical mesoporous HZSM-5 zeolites exhibited better stability than conventional HZSM-5 and excellent DME selectivity. The activity for methanol dehydration strongly depended on the textural property and acidity of the catalyst. The synthesized hierarchical mesoporous HZSM-5 zeolites exhibited better catalytic activity than conventional HZSM-5, indicating that hierarchical mesopores play an important role in the methanol to dimethyl ether process.