Study Of Catalyst Used In The Dehydration Of Methanol To Dimethyl Ether

In recent years, with ever growing concerns on energy crisis and the character of energy situation in China "coal-rich, oil-poor and shortage in natural gas", the process for the alternative coal-based fuel, dimethyl ether (DME), has emerged as an important process in chemical field with a lot of concerns. During the reaction of methanol's dehydration to dimethyl ether in fixed bed reactor, the preparation of high-performance catalyst is much important. In this thesis, sol-gel method is adopted to synthesis catalystγ-alumina, while aluminum iso-propoxide (AIP) as precursor and 2-propanol (IPA) as solvent in the prepared process. The influence of preparation conditions (the amount of H2O, pH of solution are selected as the two factors), modifier as well as operation condition on the catalytical properties are studied. The prepared catalysts are characterized by XRD, BET and NH3-TPD and the acitivity are evaluated in the dehydration of methanol to dimethyl ether in a fixed bed reactor, all these datas are correlated well with the characteristic results.(1) The catalysts prepared by sol-gel method obtain a high purity and high BET surface area.(2) During the catalyst preparation, the two factors (the amount of H2O, pH of solution) are selected to study the influence on phase formation, surface area, pore size distribution and number of acidic sites on the y-alumina. The characteristic results show that S3 prepared in this condition:H2O/AIP=4.5, pH=9, obtains more BET surface area (369.59m2/g) and more acidic sites(0.4123 mmol NH3/g), and it shows a higher activity in the reaction.(3) Based on the catalyst S3, the influence of operation conditions is studied in the fixed bed reactor at 0.1Mpa,260～320℃and weighty hourly space velocity of 2.5～10h-1. During the dehydration of methanol, the selectivity of DME is highly above 99% without any by-product. Under the same temperatue, the conversion of methanol decreases with the increase of WHSV; while the conversion increases with the temperature under the same WHSV.(4) The effect of additive modifier in the process of catalyst preparation is studied, the characteristic results shows that the additive of Si and P change the phase formation.