Fluid flow and mass transfer characteristics of enhanced CO₂ capture in a minichannel reactor

CO₂ absorption using amine solvents can be significantly enhanced by the use of microscale reactors having high surface area to volume ratio. The present paper reports an experimental investigation of the fluid flow and mass transfer characteristics during reactive gas-liquid absorption in a minichannel reactor. Absorption of CO₂ mixed with N₂ into aqueous diethanolamine was studied in a channel having hydraulic diameter of 762μm and a circular cross-sectional geometry. High-speed imaging of the two-phase flow was conducted to visualize the flow regimes. Image-processing analysis of the acquired flow patterns was performed to determine the interfacial area. The performance of the reactor was studied with respect to the absorption efficiency, pressure drop, mass transfer coefficient, interfacial area, enhancement factor, and Sherwood number. Parametric studies investigating the effects of phase superficial velocity, liquid reactant concentration, and CO₂ concentration in the gas phase were performed and are discussed. High levels of absorption efficiency, close to 100%, were observed under certain operating conditions. An empirical model for the Sherwood number was developed and compared against experimental data. The mass transfer coefficient was found to be higher at reduced channel lengths, which was attributed to improved utilization of the absorption capacity of the amine solution for a given reactor volume. The presently achieved values of mass transfer coefficient and specific interfacial area are between 1 and 4 orders of magnitude higher than those reported for most conventional absorption systems.