Preparation And Research On Si-Al Based Catalyst For DME Synthesis In Slurry Reactor

Dimethyl ether (DME) has extensive sources, it can be synthesized from coal, natural gas, coal-bed gas, biomass and other resources. Dimethyl ether is of high hexadecane value and can be used as an alternative fuel of liquefied petroleum gas (LPG) and oil.So Dimethyl ether is a kind of important material to solve the energy and environment problem in the future, being known as the clean energy of the 21st century’s.One-step synthesis of DME in slurry reactor, characterized by process simplicity and it’s low production cost, is an important route to improve the synthesis efficiency and reduce costs. However, poor stability of the catalyst is the main obstacle for its extensive industrial application. Although many scholars at home and abroad have done a lot for the problem, the deactivation of catalyst has not been fundamentally solved. Aimed at the problems of catalysts used in slurry bed and based on the concept of all materials’formation and growth are finished in the course of adapting with surroundings, a new method, named complete liquid-phase technology for slurry catalyst preparation has been developed by our group. The technology can make the catalyst materials has better rheology and stability. Previous research in our group showed that Cu-Zr, Cu-Zn-Al, Cu-Zn-Al-Zr catalysts prepared by this method used in slurry reactor have excellent stability. Subsequently, our group introduced Si-component into the catalyst system and prepared Cu-Zn-Si-Al slurry catalyst, which improved the catalytic activity and selectivity of DME to some extent, but the problem of deactivation appeared. Previous research showed that the loss of Cu component in the reaction was the reason for its deactivation. Based on the result of previous research, this paper wish to solve the problem of deactivation of Cu-Zn-Si-Al slurry catalysts through improving the preparation technology. The catalysts were characterized by XRD, XPS, NH3-TPD-MS, H2-TPR and elemental analysis. The main conclusions are drawn as follows:The catalyst whose precursor is prepared by step-by-step precipitation method has a better activity than the one whose precursor is prepared by sol-gel method, but the stability of the two has no significant differences. Different heat treatment methods have great impact on the structure and performance of catalysts. The catalyst treated in liquid phase showed better stability than the calcined one during reaction, furthermore, the former has a significant increase in the number of weak acid sites and its ability in methanol dehydration was enhanced.The raise of Si/Al ratio is beneficial to the reduction of the catalyst on the whole. Si/Al=1 is the optimum value for the synthesis of DME, which showed the highest CO conversion and DME selectivity. Different silica source affected the catalyst performance obviously. The catalyst prepared with TEOS as silica source showed higher activity than the one with silica sol as silica source, however, the latter showed higher stability in the reaction than the former. We can concluded that the dispersibility and the weak acid sites of the catalyst have great effect on its activity. In addition, no loss of Cu was found during the reaction.Mn additives have no use in improving the catalytic properties.