Direct and continuous conversion of flue gas CO2 into green fuels using dual function materials in a circulating fluidized bed system.

[Display omitted] • Direct and Continuous CH 4 production from model flue gas CO 2 using circulating fluidized bed. • Circulating fluidized bed enables steady-state cyclic operation of CO 2 capture and hydrogenation. • High-concentration CH 4 (>20 %) was directly produced from low-concentration CO 2 (2 %). • High CO 2 capture efficiency (>88 %) and high CH 4 selectivity (>99 %) were achieved. Carbon capture and utilization (CCU) technologies, such as CO 2 methanation, generally require energy-intensive CO 2 capture and separation processes prior to catalytic CO 2 conversion. In contrast, integrated CO 2 capture and reduction (CCR) technologies that use dual function materials (DFM) can directly convert low-concentration CO 2 in flue gas or atmosphere into high-concentration CH 4 or CO. In this study, we demonstrate a circulating fluidized bed (CFB) approach to enable continuous operation of CCR. In the CFB approach, the DFM (Na/Ni/Al 2 O 3) circulates between two bubbling fluidized beds to enable steady-state cyclic operation of (1) selective capture of CO 2 in flue gas/air and (2) hydrogenation of the captured CO 2. We succeeded in the continuous synthesis of CH 4 with high CO 2 capture efficiency (>88 %) and high H 2 conversion (>85 %) yielding mainly CH 4 (selectivity > 99 %) as the product at high concentration (>20 % CH 4) using 2 % CO 2 /N 2 as the model flue gas. [ABSTRACT FROM AUTHOR]