2021 Volume 54 Issue 10 Pages 541-548
A recirculation microreactor system for gas–liquid reactions has been developed, in which gas is continuously introduced into liquid, in order to effectively perform reactions with longer reaction times under slug flow at the desired volume ratio between gas and liquid. The slug flow was produced in a T-shaped mixer with an inner diameter (ID) of 0.5 mm and the obtained solution collected into a 20-mL (2.0×10−5 m3) vessel through a tube with an ID of 1 mm was introduced into the mixer again. This system was evaluated by the absorption of carbon dioxide into water. At first, this absorption with the conventional batch method was performed. It was clarified that pH decreased with time by introducing carbon dioxide. Then, the recirculation microreactor system was applied to this absorption. The solubility of carbon dioxide into water reached above the solubility equilibrium of 1.67×10−5 mol/L (1.67×10−5 kmol/m3) with both this system and the conventional batch method. However, the solubility with this system increased faster than that with the conventional batch method. The absorption rate with this system was improved by over three times compared to that with the conventional batch method. This tendency with this system and the conventional batch method was in good agreement with the reported tendencies. Furthermore, a mass transfer capacity coefficient, KLa had a peak at the flow rate of the aqueous solution of around 2.5 mL/min (2.5×10−6 m3/min), which was closer to that of carbon dioxide of 1.8 mL/min (1.8×10−6 m3/min). It would be better to perform this absorption under slug flow at a smaller volume ratio regardless of the total volume ratio between carbon dioxide and water. It was concluded that our recirculation microreactor system could effectively perform gas–liquid reactions with appropriate reaction times under slug flow at the desired volume ratio between gas and liquid.
