Fluidized bed chemical looping for CO2 capture and catalytic methanation using dual function materials

CO2 capture from combustion flue gas combined to its catalytic hydrogenation to synthetic methane is considered as a promising technology in the field of Carbon Capture and Utilization (CCU). In this work, the integrated CO2 capture and methanation process was investigated in an innovative chemical looping configuration using dual function materials (DFMs) recirculated alternately between two interconnected bubbling fluidized bed reactors. By physically separating the CO2 capture step and the catalytic hydrogenation reaction in two coupled fluidized bed reactors it is possible to effectively control and independently optimize the operating temperature of each half cycle while running the process continuously. A high-performing Lithium-Ruthenium/Al2O3 was selected to investigate the effect of the specific temperature level for the CO2 capture and the methanation phases in the range 200 - 400 ◦C, checking the stability and repeatability of the CO2 sorption and catalytic performance over 5 repeated cycles for each operating condition. Subsequently, under the best conditions in terms of methanation performance, a similar Na-promoted dual function material was also tested. The DFMs performance appeared to be quite reproducible over the cycles, but it was subject to kinetic limitations, especially in the case of Na-Ru/Al2O3. Interestingly, the methane yield approached 100 % under the highest tested temperatures for the Li-based DFM. Despite some limitations due to the experimental purge phases of the lab-scale system, the study provides the proof-of-concept of the process which enables the possibility of decoupling the two steps with the aim of a large potential intensification.