Study On Catalytic Synthesis Of Methanol Cu - Zn - Zr - O By Hydrogenation

Carbon dioxide is the main greenhouse gas for global warming. CO2 emission reduction and reutilization has always been the topic of addressing climate change and will be the key issue concerning national politics, economy and environment. This paper takes CO2 in waste gas as the carbon resource to develop high-value-added chemical products such as alcohol, ether and fluid fuel, which is of great significance to advance the CO2 chemical engineering, ease its impacts on environment and establish an effective CO2 resource utilization system. Methyl alcohol (CH3OH) is an essential chemical raw material and high-quality fuel. Chemical products derived from CH3OH can be the potential substitute for fossil fuel. Therefore, CH3OH synthesized by the hydrogenation of CO2 plays an important role in dealing with issues related to climate change, environmental protection, energy and chemistry.This paper has made a literature review and analysis on researches and application status of catalysts of CH3OH synthesized by the hydrogenation of CO2. Taking Cu-Zn-Zr-O catalyst as the core, we pertinently conduct researches on the optimization of catalysts, doping modification, preparation technology, reaction mechanism and the dynamics. The catalytic performance is enhanced significantly. Catalytic reaction mechanism is explored and the dynamic rules of reaction are revealed, which offers an important reference for the design of catalysts used on the synthesis of CH3OH by the hydrogenation of CO2.(1) Optimization of Cu-Zn-Zr-O catalyst. Coprecipitation method is adopted to prepare catalysts of Cu-Zn-O, Cu-Zr-O, and Cu-Zn-ZrO2. The influences of the proportion of ingredients on the material structure and catalytic activity are investigated and thereby the coprecipitation preparation technology is optimized based on the optimal proportion of ingredients. Interaction between Cu and other ingredients in the catalyst is closely related to the activity of catalysts in the CH3OH synthesis by the hydrogenation of CO2; the specific surface area of catalyst is not the major factor of catalytic activity. ZnO is not used to alter the pattern of Cu; instead, it helps to form the Cu-Zn active sites on the surface of copper. When the proportion of Cu/Zn/Zr is 9:9:2, it has the optimal catalytic activity. Vacuum freeze drying and ultrasonic method are capable to prepare catalysts of CH3OH synthesis of excellent performance by optimizing the preparation technology, then the methanol production rate can get 7.86% and 7.62%.(2) Modification of Cu-Zn-Zr-O catalyst. Modification of rare earth oxides and Al2O3 in Cu-Zn-Zr-O catalyst is made based on the optimal proportion of Cu/Zn/Zr 9:9:2 to investigate its catalytic activity and thermal stability. La, Pr and Nd modified catalyst is of higher catalytic activity due to its contribution to the combination of CuO and ZnO. Pr-modified catalyst has a lower reduction temperature and a higher CO2 absorptive capacity, which can reinforce the velocity of CO2 hydrogenation and thereby the optimal activity is reflected in the catalytic reaction. When the mole content of Pr is 3%, it is of better reactive activity and thermal stability. As with Al2O3 modified Cu-Zn-Zr-O catalyst, when the mass ratio of Al2O3/ZrO2 is 1/5, (CuO)9(ZnO)9(ZrO2)1.67(Al203)0.4 catalyst (CZZ-Al-1/5) has the best comprehensive catalytic activity. (4) The activity of Al2O3 modified Cu-Zn-Zr-O catalyst is close to the optimal outcome of rare earth element modification, and can enhance the thermal stability of catalysts, which enjoys certain application advantages.(3) Cu-Zn-Zr-O/Al2O3 coprecipitation technology. Coprecipitation preparation technology (precipitate temperature, ultrasonic intervention and precipitating agents) is optimized based on the optimal Cu-Zn-Zr-O/Al2O3(CZZ-Al-1/5) catalyst to investigate the catalytic reaction activity. Precipitate temperature plays a major role in controlling the crystalline growth velocity and crystalline grain size, while the intervention of ultrasonic wave in the precipitating process can facilitate the formation of precipitate and solution, and accelerate the homogeneous distribution of active constituents and carrier ingredients so as to speed up the formation of Cu-Zn-0 solid solution and reinforce the systematic effects among each active constituent. Precipitating agents neutralize the solution in the precipitating process. But precipitating agents of different cations will differ a lot in accelerating the synergistic effect among the active constituents of CuO and ZnO due to the distinctive electronic effects of cations. In the co precipitation reaction, K2CO3 was used as the precipitating agent, and the co-precipitation reaction was carried out at 70℃ with the 70% power ultrasonic, then coprecipitation method can get the catalyst with excellent physicochemical properties and catalytic properties. In the catalytic reaction, the CO2 conversion rate is 29.6%, selectivity of Methanol is 32.12%, and the final yield rate of methanol is 9.51%.(4) Reaction mechanism of methyl alcohol synthesis by CO2 hydrogenation. In-situ DRIFT analysis is used to real-time monitor the reaction intermediates during the reaction and thereby acquire relative information about the reaction mechanism. This paper proposes a reaction mechanism route chart of CO2 in Cu-Zn-Zr-O and modified catalysts of methyl alcohol synthesis. The process of the whole synthesis can be summarized as follows:first, CO2 can absorb ZnO and ZrO2, then get HCO3-Zn and HCO3-Zr by contacting with CO3-Zn and CO3-Zr. At the same time, CuO was reduced to Cu0 by H2, get the Cu0 active center. H2 Become to hydrogen ions by the active center. The reaction of hydrogen ions and bicarbonate generate formate, the reaction of formate and hydrogen ions generate methoxyl, finally the reaction of methoxyl and hydrogen ions generate methyl, and we can get by-product CO during the process of the whole synthesis.(5) Dynamic analysis of methyl alcohol synthesis by CO2 hydrogenation. Dynamic analysis of methyl alcohol synthesis by CO2 hydrogenation is made by means of gradientless reactor examination experiments, macrodynamics experiments, dynamics principles and models. The affecting mechanism of gas velocity, reaction pressure and reaction temperature on the catalytic activity is obtained. The faster the velocity of main gas is, the higher rotational speed required by gradientless reactor is; thus the control over raw gas velocity will help to realize the gradientless requirements of reactor. L-H-W absorptive double-speed macrodynamics model is used and support vector machine is adopted to acquire the parameters of macrodynamics model. Meanwhile, the validity of the model is verified. Data of computational dynamics falls in good agreement with the experimental outcomes of optimization and modification of catalysts. Apparent activation energy of CO hydrogenation and CO2 hydrogenation is 3.8872×104J/mol and 4.4156×104J/mol respectively. With the temperature increasing, the production rate of CH3OH and the conversion rate of CO2 increase first and then decrease; while with the increasing reaction pressure, the production rate of CH3OH and the conversion rate of CO2 increase significantly. Therefore, higher reaction pressure is conducive to the improvement of production.