Gas-Liquid Two-Phase Flow and Mass Transfer of CO2 Absorption into Amino Acids Sodium Aqueous Solution in Microchannel

Carbon dioxide (CO₂) is a typical greenhouse gas and the primary contributor to the global warming and climate change. It is imperative to remove huge amounts of CO₂ from the exhaust gases in many industrial processes. The amino acid salt solutions is a new type of CO₂ absorbent with advantages such as low volatility, low toxicity, antioxidant degradation and good absorption performance, which accordingly have received increasing attention. The gas-liquid two-phase flow and absorption performance of CO₂ into sodium glycinate, sodium L-alaninate, sodium L-valinate and sodium L-threoninate were investigated by a high-speed camera in a microreactor. Under Taylor-bubbly and Taylor flows, the CO₂ absorbed molar amount of four kinds of sodium amino acids at same condition decrease in the order: n(sodium glycinate) > n(sodium L-alaninate) > n(sodium L-valinate) > n(sodium L-threoninate). Furthermore, the mass transfer characteristics of CO₂ absorption into sodium glycinate aqueous solution were also investigated experimentally. The effects of gas phase flow rate, liquid phase flow rate and liquid phase concentration on specific surface area (a), liquid-side volumetric mass transfer coefficient (k_La) and liquid-side mass transfer coefficient (k_L) were studied. The results show that the larger gas phase flow rate, the smaller liquid phase flow rate and liquid phase concentration could lead to larger specific surface area. The liquid side volumetric mass transfer coefficient (k_La) increases with increasing the gas phase flow rate, liquid phase flow rate or concentration of sodium glycinate solution. The liquid side mass transfer coefficient (k_L) decreases slightly with rising gas phase flow rate, while increases with increasing the liquid phase flow rate and liquid phase concentration of sodium amino acids. A dimensionless empirical correlation was proposed to predict liquid side volumetric mass transfer coefficient considering the enhancement of chemical reaction on mass transfer.