Study On Hydrogen Production By Chemical Chain Reforming Of Methane As The Oxygen Carrier Of Magnetite Concentrate

Chemical looping reforming of methane is a novel technology for co-generation of syngas and hydrogen.One of the most important issues for chemical looping technology is to find low-cost oxygen carriers.In the present work,we use magnetite concentrate ore as a low-cost oxygen carrier for chemical looping reforming of methane.The main active component of oxygen carrier of magnetite concentrate ore is Fe₃O₄.The possibility of chemical looping reforming of methane using magnetite concentrate as oxygen carrier was investigated.The changes of chemical reactions and component contents with temperature during the cycle were described.The results showed that higher temperature had a greater influence on the reduction reaction of Fe₂O₃ with methane than the formation of carbon deposition.Methane can be obtained a higher conversion rate with an ideal ratio of syngas and inhibition of carbon deposition can be obtained at a range of reaction temperature from 700 to 800℃.The negative influence of C and Fe₃C formed in the reduction process on the quality of produced hydrogen can be inhibited by controlling the water vapor reaction temperature.The FeTiO₃,FeTi₂O₅ and Fe₂TiO₅ achieved regeneration by participating in water vapor reactions.But FeAl₂O₄ and MgFe₂O₄ are irreversible,resulting in the loss of reducible iron species.The thermodynamic calculation are in agreement with the experimental results,indicating that using magnetite concentrate as the oxygen carrier of the CLRM system is theoretically feasible,in addition,the chemical thermodynamics analysis method can be used as a guiding method for the reaction characteristics studies of chemical looping reforming of methane using magnetite concentrate as oxygen carrier for hydrogen production.The reactivity for coproduction of syngas and hydrogen was tested by an isothermal redox experiment using methane as a reducing fuel and steam as an oxidizing gas at the temperature of950℃.It is observed that the ore reaches a stable state after three cycles,the produced hydrogen and syngas in a H₂/CO molar ratio of 2.0 can be stably obtained with high selectivity,the syngas with a yield of 10.29 mmol/gand purity of 95.11%and the hydrogen with a yield of 4.94 mmol/g and purity of 96.22%are obtained.The calcinated magnetite oxygen carrier produces syngas with a yield of 10.64 mmol/g and purity of 96.30%and hydrogen with a yield of 5.25 mmol/g and purity of 96.52%.This work gives full evidence to the feasibility of using magnetite concentrates as low-cost oxygen carrier for the CLRM system.At the same time,the micro-morphology and phase evolution were analyzed to explain the factors of the performance improvement after calcinated.The kinetics study was performed on magnetite oxygen carriers.It is found that the reduction of original and recycled magnetite to wu¨stite is well represented by the phase boundary-controlled（contracting cylinder）mechanism,and the 1-D nuclei nucleation and growth integrated with diffusion mechanism can be successfully applied to describe the reduction of calcined magnetite.The activation energy for the reduction of original magnetite is93.02 kJ/mol,which slightly decreases to 86.90 kJ/mol after successive cycling due to the phase structure of the oxygen carrier tends to be stable.After ultrasonic treatment,the syngas yield increase to 13.15 mmol/g and hydrogen with a yield of 5.43 mmol/g and purity of 98.90%.In this case,physical or chemical modification on structures of the ore oxygen suggested to improving the activity of magnetite oxygen carrier for further investigation.