Study On Methanation Properties And Mechanism Of Reduction Of Carbonate With Metal Hydride

Since the industrial revolution,the development of the global economy has mainly depended on the burning of fossil fuels,this releases large amounts of carbon dioxide into the atmosphere,adversely affecting the climate and the environment.From an environmental and economic point of view,converting CO2 into methane is realistic and conducive to addressing environmental and energy issues.Methane,as the main component of natural gas,has the advantages of high combustion value and no pollution.Solid CO2(metal carbonates)is abundant,easy to transport and handle.As an excellent solid hydrogen storage material,metal hydride has higher reducibility than hydrogen and is easier to transport.At present,the technology of using metal oxides to absorb carbon dioxide to form carbonates has been gradually mature.Metal carbonates have the potential to become renewable resources for the production of fuels and chemicals,and they can be quickly replenished through the carbonation process.Thermochemical reduction of carbonates with metal hydrides was first investigated,and we successfully prepared H2 and CH4 fuel.On the above basis,the reaction cost was reduced by synthesizing metal hydride,and the methanation performance of the cyclic reaction was further studied.1.Thermochemical reduction of metal carbonates with metal hydrides was first investigated,and we successfully prepared COx-free H2-CH4 mixed fuel with high yields and selectivity.As respects to the metal carbonate-metal hydride systems,the volume energy density can reach as high as 12055.4 kJ/mol,CH4 yield can reach 84.5%with approximate 100%selectivity,and the CH4 content ranging from 8.6%to 88.1%is able to be tuned.It was confirmed that the nature of metal carbonates/hydrides,heating time and temperature,and the composition of the reaction mixture has a significant influence on methane yield and content.These results demonstrate that heat treatment of nanosized metal carbonates and activated metal hydrides is a promising process for in-situ preparation of H2-mixed CH4 fuel and CO2 utilization2.Based on the results of the previous chapter,we investigated metals induced hydrogenation of metal carbonate.The Ca-CaCO3-H2 system can achieve 91.36%CH4 yield with approximate 100%selectivity,at 500℃ under 1.6 MPa H2 after 48 h,In addition,the heating time and temperature,the ratio of reactants and hydrogen pressure has a significant influence on methane yield.This part of the study provided a new idea for carbonate methanation,and a simple and low-cost method to produce methane.3.Finally,we studied the hydrogenation of CO2 induced by hydrogen storage metals and metal oxides.The results show that in the studied reaction system,Li-Li2O/Li2O@C and Ca-CaO/CaO@C can successfully induce the conversion of CO2 to methane.Ca-CaO induce CO2 hydrogenation methanation can achieve 78.6%CH4 yield,100%selectivity,the methanation effect of the cycle experiment is stable.In this chapter,methane is prepared by metal hydride and metal carbonate as mediums,which further reduced the cost of the reaction and provides a new idea for CO2 methanation.