Direct CO2 capture from ambient air using K2CO3/Y2O3 composite sorbent

Carbonate–bicarbonate looping was tested for direct CO2 capture from air using a composite sorbent K2CO3/Y2O3. The phase composition, the porous structure and the texture of the composite sorbent were characterized by means of X-ray diffraction, mercury intrusion and scanning electron microscopy methods. The thermal properties of the sorbent were additionally studied by X-ray diffraction in situ and thermogravimetry methods. CO2 absorption from air and desorption experiments were performed in a continuous-flow system. The effect of regeneration temperature on CO2 uptake was investigated. It was shown that CO2 absorption uptake from air is about 28 mg (CO2)/g in temperature swing absorption cycles within regeneration temperature range of 150–250 °C. However, the increase of the regeneration temperature up to 300 °C results in gradual decrease of the absorption uptake down to 10 mg (CO2)/g. The XRD pattern of the cycled sample contains a set of reflections that cannot be assigned to any known potassium- or yttrium-containing crystalline phase. The new phase, which is thermally stable up to 460 °C, accumulates potassium ions and is, probably, responsible for the sorbent capacity decay.