Experimental study on gas holdup and bubble behavior in carbon capture systems with ionic liquid

Ionic liquids (ILs) have been widely considered as potential green solvents for CO2 capture, and many promising ionic liquids have been synthesized and reported. However, knowledge related to the hydrodynamics of CO2 absorption with ionic liquids especially the bubble behavior is still scarce compared with the conventional molecular solvents. In this study, it is the first time to discuss the multi-bubble behavior in a carbon capture system with ionic liquid by using a high speed image pick-up system. The bubble behavior, such as bubble size distribution, total gas holdup, Sauter diameter and interfacial area at different operating conditions are investigated. The experimental results show that the bubble diameter of CO2–[bmim][BF4] system is smaller than that of N2–[bmim][BF4] system. The bubble diameter increases as the gas superficial velocity increases and the height along the axis of the column rises, but decreases with the increase of the temperature. The total gas holdup in [bmim][BF4] increases with the increase of the system temperature due to the decrease of the ionic liquid viscosity. In addition, the gas superficial velocity improves the total gas holdup due to the higher gas momentum favors the formation of small bubbles. A new correlation based on the experimental data is proposed for the prediction of Sauter diameter in gas–ionic liquid systems. The prediction results calculated by the new correlation are in good agreement with the experimental data with a relative error less than 6%.

► Multi-bubble behavior in CO2/N2–ionic liquid system was investigated by high speed image pick-up system.
► CO2 and N2 bubble behaviors in ionic liquid system were analyzed and compared.
► The effects of varied operating conditions on bubble behavior were studied.
► A new empirical correlation to predict Sauter diameter in ionic liquid system was presented.
► The prediction of the proposed correlation agrees well with the experimental data.