Dispersion of supercritical carbon dioxide to [Emim][BF₄] with a T-junction tubing connector

The two-phase mixtures organized by ionic liquids (ILs) and carbon dioxide (CO₂) are green systems for creation and purification of fine chemicals and natural products. Owing to the very low vapor pressure of ILs, the mixture of supercritical CO₂ (ScCO₂) and IL has asymmetrical solubility, which is special for engineering application. However, due to the high viscosity of IL and the large density difference between IL and ScCO₂, they are difficult to well mix in common chemical engineering equipment. To intensify the contact of ScCO₂ and IL, we proposed a micromixing technique to disperse ScCO₂ into a representative IL, 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF₄]) as sub-millimeter scaled bubbles. The results showed that 0.3–1.2 mm average diameter's ScCO₂ bubbles were cut ruptured by the continuous [Emim][BF₄] phase in a 0.75 mm inner diameter T-junction connector. To further investigate the bubble generation law, the viscosity of CO₂ saturated [Emim][BF₄] was determined at different temperatures and pressures. The trend of size variation exhibited that the bubbles were generated from dripping flow at Ca < 0.05, but from jetting flow at Ca > 0.05. In addition, the normalized bubble diameters fit well with the two-phase microflow models obtained at atmosphere pressure.