In the present paper, we investigated CO 2 capture with 24 tertiary amine absorbents, including three synthetic amines, with systematic modification of their chemical structures. Aqueous solutions of the amines (mass fraction 30%) were used to evaluate the performance for CO 2 capture. Gas scrubbing, vapor−liquid equilibrium (VLE), and reaction calorimetry experiments were conducted in the laboratory to obtain the absorption rate, the amount of CO 2 absorbed, cyclic CO 2 capacity, and heat of reaction for each absorbent. The results for these absorbents were compared with the conventional tertiary absorbent N-methyldiethanolamine (MDEA). Seven of the investigated absorbents performed well with high absorption rates and cyclic capacities. Among these absorbents, some showed lower heats of reaction than MDEA. These results provide basic guidelines for discovery of potential tertiary amine-based absorbents that may lead to development of new absorbent systems in the CO 2 capture area.

A conductor-like screening model for real solvents (COSMO-RS) was applied to the study of the amine−H2O−CO2 system. pK a values for 25 amines including a variety of alkanolamines and some cyclic or aromatic amines were calculated by the COSMO-RS method coupled with the density functional theory (DFT). The predictions of pK a values were compared using different DFT levels for geometry optimization and also with those based on another solvation model (SM5.4/A). The DFT-COSMO calculation at the BP/TZVP level has shown a relatively good correlation with experimental values for the 25 amines (R 2 ≅ 0.8) at a low computational cost. With this method, we have developed a calculation model to predict the equilibrium ratio between carbamate and bicarbonate anions in a CO2-loaded aqueous amine solution and have confirmed the validity of the prediction model by 13C NMR spectroscopy.

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