Physical and reactive absorption of CO2 in capillaries: mass transfer, modelling and produced chemical species

Abstract

In a circular economy and sustainability context, CO2 utilization is key. For photochemical or electrochemical transformations, CO2 absorption in liquids has become crucial and even a limiting step. This work aimed to establish an average mass transport coefficient (kLa) characteristic of the CO2 absorption in water and in alkaline solutions in capillary absorbers (2–4 mm) under Taylor flow and recirculation mode. A correlation among prevailing dimensionless numbers (Sh, Re, Ca and Sc) was also established. To achieve so, the absorption of CO2 was conducted in both, water and NaOH solutions (0.5 mol/dm3), and its concentration was monitored by measuring total inorganic carbon and pH. The gas and liquid flowrates used for the tests were 1.66×10−4 L/s and 2.5×10−4 L/s, respectively. The effect of temperature was investigated in the range of 283 and 308 K. The highest kLa was found to be 12 × 10−2 and 2.1 × 10−2 s−1, for water and NaOH solutions, respectively. The modelling and simulation of the carbon species formation and production was also conducted and a determination coefficient (R2) of 0.99 was found.