The. CO <sub> 2 </ Sub> And Methanol Direct Synthesis Of Dimethyl Carbonate Studies

In recent years,much attention has been paid to dimethyl carbonate(DMC),because DMC is one of the fastest growing environmentally benign chemical products.DMC has many potential applications:first,its versatility as a reagent and a solvent.It can be used as a chemical intermediate, such as a non-toxic carbonylaring and methylating agent.Second,it is non-toxicity for human health and environment.It can also be used as a potential gasoline fuel additive which has about three times higher in oxygen content than that of methyl tert-butyl ether(MTBE).Several reaction routes have been reported for DMC synthesis so far.Among the investigated methods,the direct synthesis of DMC from CO₂ and CH₃OH is the more preferred route as it matches the view of the so-called "Sustainable Society" and "Green Chemistry".Moreover,conversion of carbon dioxide to useful industrial compounds has attracted much attention because of its environmentally benign nature (nontoxic,noncorrosive,and nonflammable) and also a greenhouse gase and a major emission product.The direct synthesis of DMC from CO₂ and CH₃OH has been attempted to match the view of the so-called "Sustainable Society" and "Green Chemistry".The activation of CO₂ is the key problem in its conversion process.Some effective catalysts,such as organometallic compounds, carbonate salts and oxides have been reported for the rifled reaction.The Ce_xZr_1-xO₂ solid solutions showed potentially higher catalytic performance.In order to further explore the relationships between the structure and the catalytic activities of Ce_xZr_1-xO₂ solid solutions as catalysts for synthesis of dimethyl carbonate direct from carbon dioxide and methanol,the fellowing work has been done in this dissertation.1.A thermodynamic analysis of the synthesis processes is carried out with the emphasis on the calculations of the effect of the addition of the 1,1,1-trimethoxy methane(TMM),trimethoxy ethane(TME),2,2-dimethoxy propane(DMP) and 2,2-dimethoxy methane(DMM) at different temperatures and pressures.Optimum reaction conditions for DMC synthesis were investigated in this work,which will provide the thermodynamic basis for designing DMC synthesis process and developing catalysts for this process.2.The Ce_0.5Zr_0.5O₂ solid solutions were prepared by a complex-decomposition method using salicylic acid,tartaric acid,adipic acid,and citric acid as complexants and cerium and zirconium nitrides as precursors,respectively.These solid solutions can be used in dimethyl carbonate(DMC) synthesis from methanol and CO₂.Combined with the characterization results by means of X-ray diffraction(XRD),Raman,SEM,N₂ adsorption-desorption isotherms,H₂-TPR and CO₂ pulse chemisorption,we discussed the relationships between the catalytic activities and catalytic properties. Results indicated that crystal structure of Ce_0.5Zr_0.5O₂ was the key factor in determining the catalytic activity for DMC synthesis.The solid solution prepared by salicylic acid as complexants and calcined at 1273 K showed a good catalytic activity for the selective DMC synthesis from CH₃OH and CO₂.Moreover,the catalytic activity of the Ce_0.5Zr_0.5O₂ was significantly decreased when phase separation as a result of the enrichment either of Ce or Zr was occurred.3.The solid solutions of Ce_xZr_1-xO₂ with various x values were synthesized by complex-decomposition and used as catalysts for the titled reaction.Combined with the characterization results by means of X-ray diffraction(XRD),Raman,SEM,mercury porosimetry, N₂ adsorption-desorption isotherms,H₂-TPR and CO₂ pulse chemisorption,we discussed the relationships between the catalytic activities and catalytic properties.Results indicated that Ce_0.5Zr_0.5O₂ with tetragonal phase exhibited very effective in methanol conversion.In order to increase the methanol conversion and the selectivity to DMC,the method of removing H₂O was used with an additive of TMM.Results indicated that,the addition of TMM was very effective for the increase of the methanol conversion.The methanol conversion increased from 1.8%to 7.9%at the same reaction conditions over Ce_0.5Zr_0.5O₂.The methanol conversion reached about 10.4%using TMM as dehydrating reagent at 423 K and 12 MPa after 34 h reaction.The combination of this selective bimodal porous catalyst with an effective H₂O removal system can provide a novel process of selective DMC production starting from CO₂ with a dramatic efficiency. The elucidation of the mechanism of the activity enhancement enables catalyst design for much higher performance.4.In order to enhance the catalytic activity,the methods of modifying the solid solutions of Ce_xZr_1-xO₂ were used.These solid solutions modified can be used in dimethyl carbonate(DMC) synthesis from methanol and CO₂.(1) The method of doping Y on Ce_xZr_1-xO₂ was used.The solid solutions of Ce_xZr_1-x-0.1Y_0.1O₂ with various x values were prepared by complex-decomposition method,and applied for the direct synthesis of dimethyl carbonate in a batch reactor under 20 MPa.The performance of Ce_xZr_1-x-0.1Y_0.1O₂ for the titled reaction strongly depends on x values and calcination temperatures, and the Ce_0.5Zr_0.4Y_0.1O₂ calcined at 1073 K showed the optimal performance.However,the catalytic activity of Ce_0.5Zr_0.4Y_0.1O₂ calcined at 1073 K was lower than the Ce_0.5Zr_0.5O₂ solid solution calcined at 1273 K. (2) The method of loading ionic liquid(ILs) on the solid solutions was used.The [emim]Br/Ce_0.5Zr_0.5O₂ catalysts were prepared by impregnation method and applied for the direct synthesis of dimethyl carbonate.The results indicated that the[emim]Br contents of [emim]Br/Ce_0.5Zr_0.5O₂ catalysts influenced the DMC formation.Moreover,the catalytic performance was higher for the solid solution loaded ILs with the[emim]Br:Ce_0.5Zr_0.5O₂=1:2 as catalyst.It may be that the synergistic effect of ILs and the solid solution improves the catalytic performance for the titled reaction.It is very interesting that the catalytic activity of the ionic liquid loaded solid solution catalyst is higher than the Ce_0.5Zr_0.5O₂ solid solution calcined at 1273 K.