Study On Methane Chemical-looping Reforming Over Cerium-based Oxygen Carrier

A fixed bed reactor under atmosphere pressure has been used to systematically study the chemical-looping reforming reaction of ceria-based oxygen carrier with methane, the conversion of CH₄ and the selectivity of and H₂, CO₂ and CO were investigated, the mechanism of the methane reaction and the effect of ceria-based oxygen carrier on preparation process were discussed by mean of thermodynamic calculation, SEM-EDS, XRD, TP, BET characterization and dynamic analysis and so forth.In order to look into the thermodynamical possibility of reactions and to analyze the effect of feed ratio on the selectivity of hydrocarbon species, the related reaction involving iron oxides and ceria oxides with different valence states in the fuel reactor and air reactor were calculated by HSC thermodynamics software, it was expected to explore theorically the reactional mechanism of oxygen carrier and the optimum feed ratio for further guiding the actual test.Firstly, using citric acid complexing method, ceric oxide was incorporated with transition metals to form an composite oxygen carrier Ce₄M₁O_? ?M= Mn, Fe, Co, Ni, Cu? so as to preliminarily screen oxygen carriers. In the perspective of the selectivity of syngas, the composite oxygen carrier Ce₄M₁O_? has better performance of methane partial oxidation. In order to further study the reaction process on ceria-based oxygen carrier, the performance of the composite oxygen carrier Ce_xFe_10-xO_? ?x= 9,7,5? with different iron contents was evaluated at 850? in an fixed bed, it was found that the methane conversion of composite oxygen carriers which were compared to CeO₂ and Fe₂O₃ increased significantly, they showed good selectivity of syngas. The XRD, BET and other characterization results of composite oxygen carriers suggest that a strong interaction takes place between iron oxides and ceria oxides. According to the evaluation and characterization results above, the mechanism of methane reaction was discusses, it was presumed that the active [C]a?H₂ and CO, which derive from Ce³⁺ and oxygen vacancy, should be responsible for accelerating reduction of the amorphous Fe₂O₃ with high reactivity, consequently, the reduction product Fe* would catalyze pyrolysis of methane, this is the main reason for the rapid increase of methane conversion.Secondly, performance of oxygen carriers after controlling the calcine temperature, altering the preparation methods, mingling with active alumina and doping active component nickel was investigated in a fixed bed, it is found that calcine temperature has a little influence on the performance of oxygen carriers, but the results of preparation method is opposite; An unexpected result was discovered that the Fe₆Al₄ prepared by citric acid complexing method exhibits the highist reactivity both methane conversion and syngas selectivity, but the detailed analysis and research is needed on this oxygen carrier; Nickel oxide was doped in oxygen carrier, reaction temperature of methane is reduced, the reaction activity of methane was increased.Finally, dynamic parameters in hydrogen reduction and methane conversion were calculated respectively by thermo-gravimetric curve and by the method of constant temperature, which provides the basic reference for subsequent researches.