Bubble Behavior Plays a Large Role in CO2 Capture
As an emerging technology, 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, the lack of knowledge related to the hydrodynamics of CO2 absorption with ionic liquids, especially the multi-bubble behavior has become a bottleneck in developing a new CO2 capture process.
Researchers with Institute of Process Engineering (IPE) discussed the multi-bubble behavior in a carbon capture system with ionic liquid by using a high speed image pick-up system for the first time. The bubble size, the gas holdup and the interfacial area in a bubble column with CO2/N2–[bmim][BF4] systems were studied at different gas superficial velocities, liquid phase temperatures and axial positions by using a high speed image pick-up system.
The results showed that an increase in gas flow rate increases the bubble collision probability, which resulted in forming large bubbles. A decrease in liquid temperature contributes to forming larger bubble. Considering the effects of both viscosity and surface tension on the bubble size in ionic liquid, the viscosity played a leading role while the surface tension seems to have much less impact on the bubble size.
The total gas holdup in [bmim][BF4] increased with the increase of the system temperature due to the decrease of the ionic liquid viscosity. In addition, the gas superficial velocity improved the total gas holdup due to the higher gas momentum favors the formation of small bubbles. This was ascribed to the fact that less small bubbles are formed at lower liquid phase temperature. The gas-liquid interfacial area in the bubble column was highly influenced by the gas flow rate and the liquid temperature. Both the gas flow rate and the liquid temperature had a positive effect on the gas-ionic liquid interfacial area.
A new correlation based on the experimental data was proposed for the prediction of Sauter diameter in gas-ionic liquid systems. The prediction results calculated by the new correlation were in good agreement with the experimental data with a relative error less than 6 percent.
The paper was published in Chemical Engineering Journal.