https://doi.org/10.1002/ghg.2059
“With CACchem and total absorption time obtained in the two systems, CACchem per unit time, termed as OAR, was calculated and they are shown in Fig. 4.
OAR increased according to Cini in the low-concentration range in the two systems, and its maximum value of the 15 wt% MDEA and TEA solutions was 14.2 and 9.8 mmol CO2·L−1·min−1, respectively. Thereafter, OAR decreased as Cini increased, resulting in a parabolic curve over the full concentration range. The curved variation of OAR occurs because the chemical absorption with tertiary amine is followed by a base-catalyzed mechanism, in which CO2 directly reacts with water to generate HCO3−, and tertiary amine acts as a catalyst in the reaction, as shown in Fig. 1. Therefore, the water concentration in the amine solution is one of the important factors that strongly affect the absorption performance, including OAR, in the two systems. In addition, the OAR of the MDEA system was always higher than that of TEA at all concentrations due to the properties resulting from the structure of the MDEA molecule, which can increase the reactivity of –OH moieties in water for absorption. Based on the parabolic curve of the OAR results, the mass concentration that maximizes OAR is 15.0 wt% in the two systems, which equates to Cini values in the MDEA and TEA systems of 1.3 and 1.0 M, respectively.”
“Figure 4 Overall absorption rate according to initial molar concentration of MDEA and TEA solutions.”