Study On Preparation Technics Of One-Step DME Synthesis Catalyst By Complete Liquid Phased Technology

Nowadays, our country is at the industrialized stage that resource are largely consumed. Energy supply has become the "bottle-neck" of the development of the national economy. Liquid fuel ,such as gasoline and diesel oil are specially lacking. So, it's an urgency to find a new energy form to substitute the lacking liquid fuel. Being rich in coal and deficient in petroleum and natrual gas, it's one of the most important solutions for China to convert the relative-rich coal into clean substitute fuel. Dimethyl ether (DME), which features in its high cetane-number and excellent power performance and low pollution, is considered to be the optimal substitute fuel for diesel oil.Slurry reactor, due to its advantages in heat transfer and isothermal operation, has been considered as one of the most promising reactors for DME production. However, the poor performance in the stability of slurry catalyst is the key problem which hindered the cosmically industrialization of slurry reactor. Our team presented a novel liquid-phase preparation method of slurry catalyst to adapt the operational characteristics of the catalyst in slurry reactor. Former research result showed that the catalysts prepared by complete liquid-phase technology have excellent stability, but low CO conversion.This paper aimed at the problems existed in complete liquid phase technology, mainly examined the effects of different ratio of CO₂, which was introduced into the heat-treatment atmosphere, on the catalysis performance, and the optimization for material ratio of CuZnAl catalyst and reduction temperature. Characterization such as XRD, BET, XPS, TPR, NH₃-TPD, CO₂-TPD was carried on several representative catalysts, and was then correlated with reactive activity. The main conclutions can be educed as following:Firstly, activity of catalyst is affected by reduction temperature. Catalyst reduced at 280℃is advantageous to both CO conversion and selectivity of DME, which would remarkably enhance the selectivity of DME. The enhancement of the selectivity of DME is mainly due to the formation of CH₄ etc, which lessened the the quantity of water in system, and debased the performance of water-gas transformation, and restrained the formation of CO₂.Secondly, Cu/Zn Ratio has significant effect on activity of catalyst. there exists an optimal range of Cu/Zn Ratio for catalyst, at which the bulk structure and surface composition of catalyst are most stable before and after reaction, and the catalysts have excellent reductive performance and moderate acid intensity, and can also remarkably enhance the selectivity of DME. The enhancement of the selectivity of DME is mainly due to the formation of CH4 etc, which lessened the the quantity of water in system, and debased the performance of water-gas transformation, and restrained the formation of CO₂. In this work, when Cu/Zn is 2:1, the performance of catalysts is best.Thirdly, The introduction of CO₂ into heat-treatment atmosphere influences obviously on the structure of catalysts before reaction but less on that of the ones after reaction, the bulk structure, pore structure and surface state will voluntarily go to same. The introduction of CO₂ into heat-treatment atmosphere restrains the water-gas shift reaction, raising the DME selectivity and right amount of CO₂ in the heat-treatment atmosphere favors the increase of DME space-time yield. In this work, when the content of CO₂ in the heat-treatment atmosphere is 50%, the performance of catalysts is best.