Enhanced CO2 selective absorption by opposing ionic liquid electrospray

Abstract

Ionic liquids (ILs) are ambient-temperature molten salts that exhibit excellent CO₂ absorption properties. Because ILs are composed of anions and cations, they have high conductivity. Electrospray is one of the key atomization techniques used to enhance the CO₂ absorption performance of ILs by increasing the specific surface area of IL nanodroplets. To improve CO₂ absorption performance further, in this study, a novel opposing-electrospray configuration was developed, in which two nozzles are placed facing each other so that the IL sprays from both nozzles interfere with each other. The effects of opposing electrospray were clarified through spray visualization, droplet diameter measurements, and CO₂ absorption performance in a flow reactor. Spray visualization shows that the opposing-electrospray configuration generates a radially wider spray owing to electric field variation and Coulomb repulsion between positively charged droplets. In addition, the enhanced atomization of the IL for the opposing-electrospray configuration was confirmed through droplet size distribution measurements. Consequently, the opposing electrospray of the IL clearly improves the CO₂ absorption amount and loading rate (the ratio of molar amount of absorbed CO₂ to that of supplied IL) owing to the enhanced atomization with a more widely spreading spray. However, when the distance between the facing nozzles is increased, the spray interference is suppressed, leading to no significant change in the droplet diameter distribution and less improvement of CO₂ absorption performance. These findings suggest that the opposing-electrospray configuration induces spray interference, which in turn enhances the CO₂ absorption by promoting radially wider spray and atomization.