Conversion Of Methane To Syngas And Oxygenated Compounds

Methane conversion can be divided into indirect conversion and direct conversion.Indirect conversion is to convert methane into syngas first,and then to produce basic oxygen-containing compounds through downstream processes,such as,Fischer Tropsch synthesis.The process of direct conversion of methane to oxygen-containing compounds is simpler,but it is more difficult.How to improve the ability of anti-carbon deposition in indirect conversion and the methane conversion in direct conversion is the challenge of current research.Methane chemical looping partial oxidation?CLPO?process uses lattice oxygen in oxygen carrier instead of gas phase oxygen to directly produce syngas with H₂/CO ratio of 2.The key of CLPO is oxygen carrier.Perovskite type oxides have adjustable structures and redox properties,and are excellent candidate materials as oxygen carriers.In this paper,the effects of A-site cation Sr substitution on La Fe_0.8Al_0.2O_3-?perovskite and B-site Sn doping on the microstructure of Ba Fe O_3-?perovskite oxygen carriers were studied respectively,as well as the performance of CLPO to syngas production.Then,inspired by the methane monooxygenase which activates methane in nature,the suitable catalyst was selected for the direct conversion of methane to methanol system,and then the reaction process was deduced.The detailed work is as follows:?)A series of perovskite La_1-xFe_0.8Al_0.2O_3-??x=0.1,0.3 and 0.5?oxygen carriers were prepared and applied in methane chemical looping partial oxidation.It was found that the oxygen storage capacity of the oxygen carriers increased from 1 mmol/g?x=0.1?to 2.7mmol/g?x=0.5?with Sr doping,and the CO selective was over 94%.The characterization results showed that Sr substitution changed the chemical state of Fe,and induced the formation cracking on Fe⁰.Combined with theoretical calculation,it was found that Sr could reduce the formation energy of oxygen vacancy in the oxygen carrier,which was beneficial for improving the mobility of lattice oxygen and the resistance of carbon deposition of oxygen carrier.The reaction performance of Ba Fe_1-xSn_xO_3-?oxygen carrier with B-site modulation in methane chemical looping partial oxidation was also investigated.It was found that the introduction of Sn increased the oxygen storage capacity of oxygen carrier from 2.6 mmol/g?x=0?to about6.5 mmol/g?x?0.6?,the selectivity of syngas from 95%?x=0?to 99%?x?0.6?,and the yield of syngas from 6.7 mmol/g?x=0?to 19.2 mmol/g?x=0.6?.The characterization results showed that Sn doping was helpful to transform reduced Fe⁰ into Fe Sn alloy,preventing CH₄ cracking and carbon deposition on Fe⁰ and thus improving the carbon deposition resistance of oxygen carrier.?)A series of metal supported carbon based catalysts were prepared by saturated impregnation.It was found that the atom dispersed Cu-CN-SAC catalyst could directly oxidize methane to methanol and other oxygen-containing compounds at room temperature when H₂O₂was used as oxidant.The yield could reach up to 43.7 mmol·g_Cu^-1·h^-1,and the turnover frequency?TOF?was as high as 2.77 h^-1.In Combined characterization with experiment,it was found that Cu-CN-SAC catalyst could effectively decompose H₂O₂ into^·OH radicals.CH₄ was activated by coordinated^·OH radicals and catalyst,and the generated^·CH₃ radicals reacted with O₂ and^·OH to form CH₃OOH and CH₃OH,respectively.