Preparation, Characterization, and Activity Evaluation of H-ZSM-5 Catalysts in Vapor-Phase Methanol Dehydration to Dimethyl Ether

Using the hydrothermal crystallization method, a highly crystalline series of H-ZSM-5 zeolites were prepared in different Si/Al molar ratios (ranging from 25 up to 250). The performance of prepared catalysts was a subject of assessment in the process of methanol dehydration to dimethyl ether (DME), where a stainless steel fixed-bed flow reactor at 573 K and 16 barg with WHSV of 26.5 h(-1) was used. The catalysts were characterized by BET, XRD, NH3-TPD, ICP, TGA/DTA, TPH, and SEM techniques. According to the experimental results, the catalytic activity and surface acidity were increased with an increase in the Si/Al molar ratio up to 125 and then decreased. The sample with a Si/Al molar ratio of 125 [H-ZSM-5(125)] exhibited the best conversion and highest activity in methanol dehydration to DME. Before a comprehensive study was made on the synthesized zeolite catalysts, the dehydration reaction with crude methanol was studied over a commercial H-ZSM-5 catalyst under identical conditions. Results show that prepared catalysts have a better performance than commercial ones.