The Experimental Studt On Chemical Looping Water Splitting Coupled With Glycerol Oxidation Reforming Using Iron-Based Oxygen Carriers

New energy technology is one of the key technology for the sustainable development of human economy and society.In new energy field,hydrogen energy technology helps to achieve the goals of carbon peaking and carbon neutrality.The production and use of hydrogen energy not only has the advantage of zero carbon emission,but also can be regenerated by wind power,photoelectric combined with water electrolysis technology.It has high value of scientific exploration and research,and is praised as the final solution of energy utilization by the research academic community.The hydrogen energy field is subdivided into hydrogen production,hydrogen storage and hydrogen usage.In terms of hydrogen production technology,the traditional methane steam reforming hydrogen production method has perfect industry and mature process.The prepared hydrogen production meets the needs of most hydrogen currently,accounting for more than 90%of the national hydrogen energy preparation.There are still other hydrogen production methods,such as water electrolysis hydrogen production,coal gasification hydrogen production and industrial by-product hydrogen production.Due to their own limitations,these methods have not yet developed into a mature large-scale hydrogen production system.In terms of hydrogen storage and transportation,the existing high-pressure gaseous hydrogen storage,liquid hydrogen storage,metal hydride hydrogen storage and adsorption hydrogen storage,high-pressure gaseous hydrogen storage is still the mainstream of commercial operation.Methane steam reforming hydrogen production technology（MSR）has the advantages of simple preparation process,continuous production capacity,large hydrogen output,mature technology,stable and safe production process.However,this method also has its weakness.For example,low hydrogen production purity,and pressure swing adsorption（PSA）is required for impurity removal in subsequent treatment.The whole process depends on the cooperation of many equipment,and its by-products CO and CO₂ are easy to cause environmental pollution.Based on metal oxide as oxygen carrier（OCs）,chemical looping water splitting coupled with glycerol oxidation reforming hydrogen production（LCWS-GOR）has attracted the interest of researchers by its remarkable advantages of direct hydrogen production.The process of chemical looping hydrogen production is divided into two stages:fuel stage and steam stage.In the fuel stage,glycerol is injected into fix bed using the peristaltic pump.The glycerol is pyrolyzed after high-temperature gasification,and catalytic pyrolysis and oxidation reforming reaction occurs with the OCs to generate syngas mainly composed of H₂ and CO and take away the lattice oxygen.After that,stop entering glycerol and purge with nitrogen and inject steam.And the reduced OCs react with it makes the lattice oxygen recovers,and the steam is partially converted into hydrogen.Finally,nitrogen is injected before the next cycle.In this paper,It was studied that the preparation method and experimental parameters of the OCs in chemical looping water splitting coupled with glycerol oxidation reforming（CLWS-GOR）and the microreaction mechanism of the experiment.Based on the literature and the actual experimental conditions,the performance experiment were carried out about Fe-Ce based OCs by sol-gel method,Fe-Ce-Ni based OCs prepared by sol-gel method,Ce-Ni modified Fe-based OCs prepared by sol-gel method combined with impregnation method.The experiment included three cycle stability experiments in the long-term fuel stage,seven and fifteen cycle experiments in the short-term fuel stage and the experiment of introducing steam reforming according to water-gas shift enhancement.These samples were characterized by BET,XRD TEM and EDS before and after the experiment.The experimental and characterization results show that the Fe-Ce based OCs without Ni has higher syngas and hydrogen production than the pure Fe-based sample,which verifies the role of Ce in promoting oxygen migration described in the references.but the multi-cycle performance of the OCs gradually decreases,and the hydrogen production after multiple cycles drops to the similar yield of the pure Fe-based sample.Fe-Ce-Ni based OCs shows excellent redox performance and plays an important catalytic role in the partial oxidation and decomposition of glycerol at 750℃.The OCs with100:10:3 of Fe-Ce-Ni molar ratio showed the best oxygen transmission capacity and the highest hydrogen and syngas production.The average hydrogen production of water splitting per cycle was 11.79 mmol/g,and maintained the high conversion of glycerol and the selectivity of syngas.The amount of hydrogen produced in the steam stage of Ce-Ni modified Fe-based OCs is between 12.49-12.96 mmol.However,the performance of samples with different proportions in fuel stage is:With the increase of Ce and Ni doping,the generation of hydrogen and CO in the fuel stage increases,and the possibility of pure hydrogen pollution caused by carbon deposits released in the subsequent steam stage also increases.Simultaneously,the sample was subjected to water-gas shift（WGS）experiment with chemical looping steam reforming（CLSR）.The H₂/CO ratio in the product can be easily adjusted by the molar ratio of steam to carbon（S/C）,but the subsequent activity of OCs deteriorates gradually in multiple cycles because of the influence of steam introduction.In general,the OCs F_C52 sample prepared by the combination of metal chelating sol-gel and isometric impregnation has the best comprehensive performance in the CLWS-GOR process.