Alpha effect-driven enhancement of CO2 capture kinetics and size-controlled NaHCO3 crystals: Promoter-added NaOH absorbent study

In this study, the kinetics of the transition of Na2CO3 to NaHCO3 were enhanced based on the alpha effect by adding rate promoters to NaOH-based absorbents. Because the α-effect shows strong correlation with the electronegativity of the α-atom, to analyze their kinetic improvement, H2O2, NaOCl, and H3BO3 were selected as rate promoters. The promoters were chosen based on compounds with an O− or OH– group that can act as a Lewis base when CO2 acts as a Lewis acid or a structure that is easily accessible to CO2 molecules. Each promoter was added at different concentrations (0.05, 0.1, and 0.2 M), and the reaction rates of the absorbent solutions were experimentally evaluated. Among selected promoters, H2O2 exhibits the greatest effect, achieved the highest conversion efficiency, which showed an approximately 45-fold increase in reaction rate compared to the promoter-free NaOH solution. Furthermore, the enhancement in reaction rate allows the particle size to be controlled and precipitated with different crystalline structure. Therefore, the introduction of a promoter based on the α-effect not only significantly improves the reaction rate leading to NaHCO3 formation but also allows control of the crystal size and shape. This breakthrough can be a promising solution to address the limitations of conventional NaOH absorbents.