Synthesis,Characterization And Methanation Performance Of Nickel-based Catalysts

With the improvement of people's living standards and the rapid development of industrialization,the consumption of natural gas showed an upward trend.However,there were some troubles for traditional coal chemical technologies such as low energy utilization rate and serious environmental pollution.As we know,the Synthetic Natural Gas Technology?SNG?is a process for preparing natural gas by coal,in which the products can not only solve the problems that the natural gas shortage,but also have an important meaning to Chinese resources,energy conservation,emission reduction and full utilization of green chemicals.At present,the SNG technology is not fully mastered by enterprise in China,because that the technology remains in the development of low-temperature methanation.Therefore,the development of methanation-based catalysts with high-performance and high-temperature characteristics is extremely urgent.In this thesis,two aspects have been explored:firstly the nickel-based catalyst carrier was prepared by co-precipitation method,then with different masses of metal oxides such as Mg O,La₂O₃ and Ce O₂ were loaded on the catalysts.The mechanical strength and other properties of the Ni catalyst was characterized by the S_BET,H₂-TPR,NH₃-TPD,TG,XRD,SEM and XPS.And the catalytic performances was evaluated in a fixed bed reactor by orthogonal test.The results showed that the optimum ratio of conversion and selectivity was:5%Mg O,1%La₂O₃,4%Ce O₂;the conversion rate of CO was 98.4%,and the selectivity of CH₄was 96.9%.The addition of Mg O made the Mg Al₂O₄ spinel under high temperature calcination,which reduced the possibility of sintering of the catalyst.The addition of La₂O₃ contributed to the reduction,weakened the acidity,and prevented the carbon deposition of the catalyst.Additionally,the addition of Ce O₂increased the pore size of the catalyst and increased the conversion rate of CO.The electron effect generated by Ce O₂ increased the reducing ability of the Ni species and also reduced the probability of carbon deposition in the catalyst.On the other hand,the reaction conditions of the nickel-based catalyst were optimized and screened by a control experiment.It was found that the suitable reduction temperature of the sample catalytic reaction was 500°C,the reduction pressure was 2MPa,the reduction space velocity was 2000h^-1.The suitable reaction temperature for the sample catalytic reaction was 450°C,the reaction pressure was 2MPa,the reaction gas space velocity was 6000h^-1,and the suitable hydrogen-carbon ratio in the catalytic reaction raw material process gas was 3:1.Under this condition,the catalyst with high selectivity of CH₄.Based on the experimental results,the equilibrium constant and equilibrium conversion of methanation was calculated by thermodynamics,high catalytic performance of nickel-based catalysts compared with experimental results.Finally,a 72 hours stability test was performed on the selected catalyst sample,and it was found that the conversion rate of CO and CH₄ selectivity were small,which indicated the feasibility of the catalyst under the operating conditions.