CO ₂ absorption performance enhancement by dodecane nanoemulsion absorbents

Among the CO ₂ capture technologies, the physical absorption is one of the most common absorption methods. However, the physical absorption process is operated at extremely low temperature, and therefore huge freezing energy is required. The objective of this study is to develop the nanoemulsion absorbents that can be operated at room temperature. The nanoemulsion absorbents are prepared by the ultrasonication method. Based on the chemical properties, Span 60 and Tween 60 are added to maintain a good dispersion stability. CO ₂ absorption experiments using a porous nozzle absorber are conducted for various dodecane concentration (0.005-0.5 vol%) and CO ₂ flow rate (0.06-0.12 g/s). It is found that the CO ₂ absorption performance of 0.05 vol% nanoemulsion absorbents is 10% higher than that of pure methanol. Through the single CO ₂ bubble absorption visualization experiments, it is confirmed that the nanoemulsion absorbents cause faster bubble absorption than pure methanol does. The turbidity index (Nephelometry turbidity unit) of nanoemulsion absorbents is kept constant for seven days, which means a good dispersion stability. The enhancement mechanism of CO ₂ absorption is explained based on the Einstein-Stokes' equation, cryogenic transmission electron images, and droplet size measurements. The key idea is that nano-sized dodecane (64 nm) absorbs the CO ₂ molecules and transports it to the bulk region by the Brownian diffusion. A random walk model is used to investigate the droplet size prediction and CO ₂ absorption performance enhancement.