https://doi.org/10.1016/j.petlm.2016.11.002
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Absorption rate and absorption capacity are desired properties of an optimized blended aqueous amine solution. Absorption rate determines the amount of absorbed CO2 per liter of amine solution per unit time (mol CO2/l-amine solution/min), while the absorption capacity quantifies the maximum capacity of the amine solution per unit volume (mol CO2/l-amine solution). Nwaoha et al. defined absorption capacity as the equilibrium CO2 (αCO2, mol CO2/mol amine) multiplied by the amine concentration (Camine, mol/L) as seen in Eq. (8) [111]. This will enable a fair comparison between amine solutions of different concentrations. When amine solutions of same concentration are compared, the equilibrium CO2 loading can be used as a comparison criterion.(8)AC =αCO2×Camine
Some researchers have used the term initial absorption rate to quantify how fast amine solutions can absorb CO2 [57], [69], [111], [149]. This involves plotting the CO2 absorption capacity against time. The slope calculated from the plot’s initial straight line portion before the amine reaches equilibrium is taken as the initial absorption rate. Typical plots of CO2 absorption capacity and time are shown in Fig. 12. The CO2 absorption capacity can be taken within any short time interval (e.g. 5–20 min) during the experimental run. Therefore, higher slope translates to higher initial absorption rate. Based on the purpose of any study, the initial absorption rate can be the slope of the straight line at a particular time. For instance, from Fig. 12, the initial absorption rate of Amine A can be compared to that of Amine B based on the first 60 min. Alternatively, both amines can be compared based on the slope of their straight lines (absorption capacity vs time plot) before it starts leveling off (equilibrium). This means that for Amine A only the slope of the first 60 min will be considered while that of Amine B will be the slope of the first 80 min. Any method used should be consistent with all the studied amine solutions for fair comparison. It is also important to state that the time interval when taking the absorption capacity should also be consistent with all investigated amine solutions.
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