Effect Of The Structure Of Cu/AC Catalyst On Oxidative Carbonylation Of Methanol

Dimethyl Carbonate(DMC),as a green and environment-friendly organic compound,attracts broadly attention in domestic and overseas.It contains many functional groups such as CH3-,CH3O-,CH3OCO-,so it is of good properties and high value.DMC can be used as the substitute of toxic phosgene for the carbonylation reagent in the synthesis of polycarbonate and isocyanic acid ester.Meanwhile,DMC also can be used as gasoline addictive to increase the octane number,for its high content of O and high solubility.In addition,DMC,as a excellent solvent,can be mixed with and dissolve other organic reagents.Besides,DMC is less toxic and a outstanding degreasing agent.Thus,the application of DMC is extensive.At the early stage of DMC synthesis,the homogenous phase catalysts like CuCl or CuCl2 were applied.Though they showed well performance,it was difficult to separate and the loss of anion Cl-caused corrosion of reactor,inactivation of catalyst and other issues,which limits the industrial application of the homogenous catalysts.Afterwards,researchers improved the situation by adding promoters,ligand or other methods,but the results were unsatisfied.Therefore,researchers have turned to the field of catalyst of free chlorine.In our research group,free chlorine copper reagent(like copper acetate)was used as the precursor and activated carbon was used as the supporter in the early time.Catalysts like Cu2O/AC,Cu0/AC,CuO/AC were made through thermal decomposition of copper source and reduction of cupric ion by hydrazine hydrate and polyhydric alcohols,all of which showed high catalytic activities.Compared with the catalysts with chlorine,the catalytic activity of catalysts without chlorine is lower.Therefore,in this dissertation,based on our former researches,the influences of adding sequences and the amount of promoter Zn were studied in the high pressure batch reactor.In addition,the different synthesis pathways of catalysts and the modification of supporter were studied in the bench scale of slurry bed reactor.At the primary reaction time,the catalytic activities varied among different catalysts,while the catalytic activities tended to convergence during the stable reaction time.In order to improve of catalytic activity in the stable reaction time for the further research,the comparison of the structure and appearance of different catalysts in the stable reaction time was made in this dissertation,and the factors that effects catalytic activity in the stable reaction time were analyzed.On the other hand,the effects of varied amount of methanol and water in the feed on the DMC yield were studied as well.The final conclusions are as follows:1.With consecutive impregnation procedure applied to produce the catalyst,it turns out that the active species on the surface of catalysts are not dispersed well,the copper particles are large,and the catalyst shows low catalytic activity.While the catalyst shows high catalytic activity even without the promoter Zn through the co-impregnation procedure,which has a high Cu dispersion and is in small particles.2.Adding appropriate promoter Zn content can help to promote the reduction of CuO into Cu0,and the optimal promoter Zn content is 2%.When the promoter Zn content is 4%,the amount of crystallographic CuO increases,which impedes the reduction of CuO in turn,and it makes amount of Cu0 decrease causing the decline of catalytic activity.At the same time,it also results in combination of crystallographic ZnO and Cu to form larger particles.3.By condensing the concentration of impregnation liquid,the increase amount of Cu results in the improvement of catalytic activity and the optimal concentration of impregnation liquid is 0.16 mol/L.The loaded amount of Cu can be increased by twice impregnation and calcination procedure and equivalent-volume impregnation procedure.But it doesn't contribute to dispersion and reduction of Cu species,which leads to low catalytic activity in the primary reaction time.4.From the analysis of the structure and appearance of pre-reaction and post-reaction catalysts,it suggests that the loss of Cu species ranges from different catalysts during the reaction.However,when the loaded amount of Cu is low,the loss of Cu species is not the main contribution to inactivity of catalyst.The Cu species will be dispersed again in catalyst during the reaction in the slurry bed reactor system.