Carbon Dioxide Capture by Recovered Calcium Oxide from Waste Oyster Shells via Microwave Calcination

Calcium looping cycle, post-combustion is an emerging, energy-efficient, low cost, technology which used CaO as regenerable sorbents of CO2 capturing through the carbonation/calcination reaction cycles. The cost, stability and sustainability of the sorbent are important in the design of these systems. In this study, waste oyster shell was used as raw material for calcium-based sorbent and microwave thermal treatment was applied to the calcination process. The simulated sintering conditions of sorbent occurred in the calcination reaction process and the higher heating temperature resulted in more particle expansion and sintering. Microwave irradiation heating of sorbent was proposed to lower the operating temperature of the calcination and aimed to prevent the absorbent from sintering. The sorbents were characterized using thermogravimetric analysis (TGA), X-Ray diffraction (XRD), scanning electron microscopy (SEM), and tested in the carbonation-calcination cycles. In comparison to the conventional calcination, microwave thermal treated sorbents showed better conversions after a longer series of capturing CO2 cycles and more efficient approach to reduce the electric energy consumption and process time. CO2 capture using oyster shell powder as a sorbent was investigated during the cyclic calcination/carbonation process. Oyster shell powder have higher carbonation conversions than commercial CaCO3 after third calcium looping cycle at the same reaction conditions. Impurity can improve the carbonation conversion of calcium-based sorbents, and this may be a factor contributing to the shells demonstrating a better cyclic CO2 capture performance.