Study On The Effect Of Si And Al Resources On Catalysts Prepared By Complete Liquid-phase Technology For DME Synthesis By One Step Method

With the rapid development of the economy and the world’s largestconsumer population, China has become the first energy consumer country. Itis urgent to develop and utilize the new energy and look for alternativeoil-based fuel. Dimethyl ether (DME), which has a high cetane number andexcellent combustion properties, has attracted more and more attention.Developing coal-based synthetic gas can not only tackle the problem of oilshortage caused by energy crisis, but also achieve the goal for using coal in anefficient and clean way. Besides, it can also promote the rapid development ofcoal-chemical industry and improve the quality of energy structure security,which can exert a significant role in economy and strategic in our country.In the process of the synthesis of dimethyl ether, one-step synthesis ofDME in slurry reactor is characterized by its wide range of raw materials, lesscarbon in the catalyst surface, good performance of heat transmission, simpleoperation process and the low production cost, which has become a vital and hot research field at home and abroad. However, the traditional catalystscannot well be adapted to the slurry bed, which has restrained the industrialapplication of catalysts. Recently, our group has presented a new technologyfor slurry catalysts in the slurry bed named complete liquid phase technology,which is derived from the concept that the formation and growth of substancesare finished in the course of adapting to their surroundings. This technologycan solve the problem of low stability of catalysts in the slurry bed. Afterwards,the preparation method of precursors of catalysts in complete liquid phasetechnology has been improved. In the process of catalyst preparation, thepre-alcoholysis of AIP can improve the activity of the catalyst, but it isdifficult toreproduce the catalyst with best performance. In the later time, wefound that the commercial AIP itself caused the problem, which showeddifferent structure after aging by different time.In this paper, adding different series of silica sols, adding methods and theamount of acid silica are studied. However, the commercial AIP show the poorstability, which influences the reproducibility of catalysts with highperformance. Therefore, AIP is prepared by our own methods in order to solvethe problem. The catalysts with different existing states of AIP obtained bycontrolling aging time are prepared. The different catalytic performances withdiverse states of AIP using aluminium powder as the resource are alsoresearched. At the same time, Cu/Zn/Al catalysts prepared by AlOOH are putinto reaction. These catalysts are characterized by XRD, XPS, FTIR, H2-TPR, NH3-TPD, N2adsorption, XPS and TEM respectivity. The main conclusionsare as follows:1. The performance of catalyst show a big difference, when the acid andalkaline silica are added into the Cu/Zn/Al catalyst. The alkaline silica haslittle influence on the catalytic performance, however the acid silica sol, whichis put into the similar environment with precursor preparation, has themagnificent role in the Cu/Zn/Al catalyst, which exhibit high catalyticperformance. When the acid silica sol is mixed with AIP in the pre-alcoholysisand Si/Al is equal to one, the CO conversion and DME selectivity reachmaximum, being65.38%and76.26%respectively. In DME synthesis reaction,it is found that the acid silica sol can increase the ratio of the weak acidic sitesand the strong acidic sites on the catalysts, which promotes dehydrationperformance of methanol and the selectivity of DME.2. The difference between the acid and alkaline silica sol on the particlesize and structure, resulting in different interaction in Cu/Zn/Al catalysts anddifferent catalytic structures. Introducing the acid silica into the acid Cu/Zn/Alsystem can maintain large part of Si-O-Si structure, while Si species inCu/Zn/Al system has stronger interaction with Al species and generated largeamount of Si-O-Al. It is no wonder that the two forces in the catalysts, whichcan influence the interaction between Cu component and other components,resulting in the low valence of Cu in the catalyst prepared with acid silica sol.Meanwhile, a variety number of exposed Cu surface can make the easy adsorption and activation of CO in the reaction.3. In the complete liquid phase technology, Si species are introduced inthe catalysts, which can reduce the adsorption of paraffin in the pore,providing more active sites for CO adsorption. Besides, the best catalyticperformance of catalyst shows the least increasing of the specific surface areain the reaction.4. Due to the aging effect, the existing states of the home made AIP haspresented liquid state, crystalline state and solid state. Then the Cu/Zn/Alcatalysts were prepared with the diverse existing states AIP as the aluminumresource. The crystalline state AIP used for catalyst shows the best catalyticperformance, and the solid state AIP made for catalyst also show the goodperformance. Home-made AIP can not only solve the poor reproducibility forcatalyst, but also reduce the cost of catalyst. In addition, it can also enrich theunderstanding of metal alkoxides, aluminium sol and pharmaceuticalsynthesis.5. When the Cu:Zn:Al is2:1:4, the catalyst prepared by Al powder forAIP was beneficial to the formation of DME, while the AlOOH made by Alpowder showed high catalytic performance in the synthesis of methanol.