(623g) Study on CO Conversion from CO2 By Chemical Looping Process

Currently, in order to reduce CO₂ emissions in the worid, research and development of more efficient power generation technologies and renewable energy technologies that do not emit CO₂ are being conducted. The research and development of high efficiency power generation technology conducts improving the performance of turbines used in thermal power plants, and the research and development of renewable energy technology conducts photovoltaic power generation, wind power generation, and biomass power generation. Particularly, research on renewable energy technology has been carried out actively, and the development of virtual power plants (VPP) for electricity exchange has been carried out. In the future, thermal power generation is expected to be replaced by renewable energy sources as the main source of electricity supply, and power generation plants using fossil fuel are expected to decrease. However, since renewable energy converts energy such as sunlight into electricity, the renewable energy itself has only value as electricity. On the other hand, fossil fuels are not only used as a fuel source for thermal power generation, but also in the manufacturing industry, with the steel industry as a typical destination. In the steel industry, fossil fuels are used as blast furnace fuel and in blast furnace as coke feedstock which is an iron ore reducing material. As can be seen from the fact that fossil fuels are coke feedstock, fossil fuel contains carbon atoms that can be converted from gasification reactions to syngas and converted into chemical products, and thus have value not only as a fuel but also as a raw material for chemical products. The demand for fossil fuels in the manufacturing industry will not disappear even if CO₂ emission free power generation is achieved through the advancement of renewable energy technologies. On the contrary, the demand for fossil fuels is expected to increase with the economic development of developing countries. As the global CO₂ emissions are expected to increase, not only renewable energy technologies to reduce CO₂ emissions in the power generation sector, but also carbon dioxide capture and storage (CCS) and carbon dioxide capture and utilization (CCU) technologies to reduce CO₂ emissions are attracting attention. CCS is a technology to separate and store high concentrations of CO₂ emitted from thermal power plants in the ground, but it will take more than 10 years to determine if the area is capable of storage, and it is estimated that it will be difficult to secure storage capacity. Therefore, CCU designed for effective utilization of CO₂ are more important than CCS that only store CO₂. CCU are currently being studied for biofuel production by microalgae and natural gas reforming, which can produce CO from fossil fuels. CO can be converted into not only a fuel but also a chemical product by the conversion process. CCU has received a lot of attention, but there are still challenges. Biofuel production by microalgae has not been put to practical use on a scale that can significantly reduce CO₂ emissions due to its slow CO₂ conversion rate. Although natural gas reforming is a thermochemical reforming process and therefore has a faster CO₂ conversion rate than biofuel production by microalgae, it is essential to combine natural gas reforming with unused waste heat, such as industrial waste heat, because of the need for an energy source. Water gas reverse shift reaction is one of the existing technologies for CO production using CO₂. Since water gas reverse shift reaction is an equilibrium reaction, the removal of compounds other than CO is necessary, and it remains a problem as a CO production process. Water gas reverse shift reaction chemical looping process (RWGS-CLP) has been developed while the CO₂ based CO production technology still has some problems. RWGS-CLP is a process to produce CO by transferring oxygen between H₂ and CO₂ using an oxygen carrier, instead of reacting H₂ and CO₂ at the same time, as in water gas reverse shift reaction. In RWGS-CLP, it is a process to produce CO by reduction the oxygen carrier with H₂ and then oxidization oxygen carrier with CO₂, and since the redox reaction is separated, CO can be produced at high concentrations with few impurities in the production gas. In previous studies, iron-based composite oxides containing La and Sr have been used as oxygen carriers, but La and Sr are not economical due to their high cost. In this presentation, RWGS-CLP was performed using iron-based composite oxides containing inexpensive Ca and Zn as oxygen carriers, and CO₂ was reduced to CO. The iron-based composite oxide containing Ca is called calcium ferrite and is used for chemical looping combustions, and it is reported to have high oxygen transfer rate. Although it has been reported that iron-based composite oxides containing Zn were capable of redox at 573 K, there is no report of their application in RWGS-CLP. In this presentation, the reaction behavior of these oxygen carriers in the redox reaction with H₂ and CO₂ and their physical properties after redox are evaluated, and the performance of the various oxygen carriers in RWGS-CLP is reported. In the experiments, thermogravimetric analysis and GC analysis using fixed bed reactor were carried out. In thermogravimetric analysis, the oxygen carrier was set in the thermogravimetric analysis device, and it was evaluated reaction rate under isothermal conditions. In GC analysis using fixed bed reactor, the redox reaction was carried out under isothermal conditions, and the gas composition of the production gas was analyzed by GC.