Cu–Si–Al Alloy-Based Phase Change Composite for the Chemical-Looping Reverse Water–Gas Shift Process

Using chemical looping for a reverse water–gas shift reaction enables a higher CO₂ conversion than that expected from the thermodynamic equilibrium of the process. In addition, direct mixing of gaseous oxidizing and reducing agents does not occur, thereby facilitating gas separation. However, the CO₂ reduction reaction is exothermic, and a considerable amount of heat is generated with a high CO₂ conversion efficiency. The generated heat causes repeated temperature fluctuations in the reaction system, which are associated with the formation of hot spots. This paper describes a study that demonstrates an efficient chemical-loop CO₂ decomposition system with passive thermal regulation in a packed-bed reactor using Cu–12.8mass% Si–20mass% Al alloy-based microencapsulated phase-change materials (MEPCMs) with a eutectic temperature of about 772 °C as a heat-regulating medium. The prepared MEPCM composites displayed thermal durability of 3000 cycles and redox cycle durability of 6000 cycles. Additionally, the performance of a mixture of oxygen carriers and MEPCM composites was experimentally investigated in a bench-scale packed-bed reactor. A CO₂ conversion of more than 90% was confirmed. Furthermore, the formation of hot spots was prevented, and the packed-bed temperature in the height and radial directions remained constant at approximately the melting point of the MEPCM. These results demonstrate that the combination of the chemical-loop system and the MEPCM provides a new highly efficient CO₂ conversion system with thermal regulation functions.