Mass transfer performance enhancement by nanoemulsion absorbents during CO₂ absorption process

In this study, nanoemulsion absorbents (silicone oil/methanol) were manufactured by adding nano-size oil to absorbents for CO₂ absorption performance enhancement. To evaluate the dispersion stability of the nanoemulsion, oil droplet size measurement, turbidity measurement, and Tyndall effect visualization experiments were conducted. The effect of the ratio and concentration of oil and surfactants on the mass transfer enhancement was evaluated through thermal conductivity measurement using the transient hot wire method and the visualization analysis of CO₂ bubble absorption. The oil (silicone) and surfactant ratio of 2:1 was found to be the optimum condition through the results of dispersion stability analysis. In the CO₂ bubble absorption results obtained through the visualization analysis, the nanoemulsion with 0.01 vol% oil concentration showed the most significant absorption performance improvement. It was found that nano-size oil dispersion contributed to mass transfer enhancement, which was caused by the convective motion of nano-size oil droplets, not by enhanced thermal conductivity. Finally, the mechanisms of mass transfer enhancement by nanoemulsions are proposed, and it is concluded that the CO₂ absorption performance is enhanced by the shuttle effect and the hydrodynamic effect by the nanoemulsion absorbents.