Synthesis of Dimethyl Ether via Methanol Dehydration over Combined Al2O3-HZSM-5 Solid Acids

Combined Al2O3-HZSM-5 solid acids were prepared and used for methanol dehydration to dimethyl ether (DME) in a fixed-bed reactor. The physicochemical properties of the combined solid acids were characterized by X-ray diffraction, field emission scanning electron microscopy, N2 adsorption, and NH3 temperature-programmed desorption. Al2O3 was highly dispersed in Al2O3-HZSM-5 after impregnation (Al2O3-HZSM-5-IM), while a layered Al2O3-covered HZSM-5 structure solid acid was synthesized via chemical precipitation (Al2O3-HZSM-5-CP). Both the combined Al2O3-HZSM-5 solid acids prepared by impregnation and chemical precipitation have a higher surface area and more meso- and macropores. The combined Al2O3-HZSM-5 solid acids exhibit higher methanol dehydration activity than pure Al2O3 and it possesses higher stability than pure HZSM-5 at a lower temperature (235 (C) and a higher LHSV (30 h−1). The stable DME productivities for Al2O3-HZSM-5-IM and Al2O3-HZSM-5-CP at 235 (C reached 12.7 and 13.5 g/(g·h), respectively.