Kinetic Study of CO₂ Absorption in Aqueous Benzylamine Solvent Using a Stirred Cell Reaction Calorimeter

In the literature, aqueous amine absorbents are widely used for post-combustion CO₂ capture. Recently, benzylamine (BZA) aqueous solutions have been identified as promising solvents for CO₂ capture. In this work, the kinetics of CO₂ absorption in aqueous BZA, containing a primary amino group, has been studied using a stirred cell reactor with a horizontal gas liquid interface in a reaction calorimeter. Experiments were performed over a temperature range from 303.15 K to 333.15 K and the amine concentration ranging from 5 mass % to 30 mass %. Absorption rate experiments were performed in the pseudo-first-order regime to determine the overall kinetic rate constant using a fall-in-pressure technique. Both the zwitterion and termolecular mechanisms were applied to model the kinetic data and to estimate the individual reaction rate constants from experimental overall pseudo-first-order rate constants, <i>k</i>_OV. The experimental kinetic data are better correlated by a termolecular mechanism (AAD 14.7%) compared to a zwitterion mechanism (AAD 38.02%). The density and viscosity of pure and aqueous binary mixtures of BZA are also measured over experimental temperature and concentration ranges. Empirical models are proposed to predict pure component density and viscosity data with AAD of 0.006% and 1.16% respectively. A Redlich–Kister type equation in terms of molar fraction is fitted to experimental density data, and the viscosity data for binary mixtures are correlated with Grunberg–Nissan model with AAD of 0.02% and 5.05% respectively. The reaction activation energy (<i>E</i>_a) calculated from the Arrhenius power law model are 25.82 and 25.98 kJ/mol for zwitterion and termolecular mechanisms respectively, which indicates a lower energy barrier (∼26 kJ/mol) for the BZA–H₂O–CO₂ reaction system