Towards the integration of direct air capture and CO2 mineralisation processes employing potassium glycinate, and α- and β- alaninate

In the present work, three potassium salts of glycine, α-alanine and β-alanine were studied for an integrated direct air capture (DAC) – CO 2 mineralisation process. The influence of steric hindrance in amino acid (AA) salt solutions on mineralisation of absorbed CO 2 was investigated by employing CaO and MgO as the CO 2 mineralising agents. The overall mass transfer coefficients (K ov ) for DAC concentrations (200 – 800 ppm) of CO 2 were measured using a wetted wall column (WWC) with partial regeneration of the absorbents observed after mineralisation with MgO. An improved mineralisation was evidenced by the formation of bicarbonate species in CO 2 -loaded AA salt solutions, supported by nuclear magnetic resonance (NMR) analysis. When CaO was used as the mineralising agent, the sterically hindered potassium salt of α-alanine solution resulted in the highest CO 2 removal (approximately 60%) after 50 min of reaction and filtration. Solid products of mineralisation reactions were analysed using powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). High purity calcite (CaCO 3 ) was obtained for the solutions stored for 7 days after the mineralisation reaction.