CO2 capture results using EDA at different CO2 concentrations

Figure 3 shows the characteristic curves obtained during the CO2 capture testing using EDA. Figure 3a depicts the drop in pressure as a function of time. The drop in pressure was proportional to the amine concentration. For the 20 wt.% amine solution, the gas consumption represented a pressure drop of ~50% from the initial pressure. Figure 3b shows the temperature profile in the first 5 min of the CO2 capture process, where a “sudden” temperature increase was observed in the initial moments of the CO2–liquid solution contact. The highest temperature points were reached approximately one minute after the CO2 pressurization, being proportional to the amine concentration. The maximum value reached was ~324 K for the 20 wt.% amine solution, representing a ΔT=21 K. The temperature increments were related to the exothermic reaction between the CO2 and the aqueous EDA solutions. Similar behavior was observed in the absorption processes of CO2 [42] and other gases [43] in aqueous amine solutions. This exothermic phenomenon must be considered in the design of absorption towers for CO2 capture using amines, since “one of the most important considerations involved in designing gas absorption towers is to determine whether temperatures will vary along with the height of the tower due to heat effects; note that the solubility usually depends strongly on temperature” [44]. A more detailed analysis of the exothermicity effect is presented in Section 3.3.”


Figure 3c shows the CO2 removed as a function of time. The amount of CO2 captured was proportional to the concentration of the amine solution due to the EDA–CO2 chemical affinity. Kumar et al. [22] proposed the use of EDA as an activator in the CO2 capture process by increasing the solubility capacity of CO2 in the amine aqueous solutions (chemical solvents). Snapshots of the aqueous amine solutions were taken at the end of the experiments (see Figure 3d). An increase in the intensity of a yellowish-brown color (amber color) could be observed with the naked eye in the aqueous amine solutions. The variability in the color intensity was proportional to the amine concentration, which correlates with the amount of CO2 captured.

Table 2 summarizes the kinetic and thermodynamic data obtained from the CO2 capture testing using EDA. The CO2 capture rate (dn/dt) varied with the EDA concentration, obtaining the highest rate at 10 wt.%. Surprisingly, at the 20 wt.% amine concentration, the CO2 capture rate was the lowest, but the CO2 removed from the gas phase at equilibrium was the highest. A higher amine concentration increases the viscosity of aqueous amine solutions, unfavorably affecting the CO2 mass transfer rates [20,45]. Moreover, at 20 wt.% amine concentration, there was a more significant temperature increase in the liquid solution (see Figure 3b), which might directly affect the CO2 capture kinetics. Fan et al. [46] reported a decrease in the CO2 capture rate using alkanolamine aqueous solutions (e.g., MEA and diethanolamine (DEA)) with temperature increases. In all of the EDA aqueous solutions studied, the t90 parameter was less than 300 min (<5 h). The time required for CO2 capture can be reduced in stirred experimental setups or continuous processes at different scales, i.e., pilot-plant-scale [47,48,49] or large-scale [50,51,52]. The CO2 removed and the CO2 loading were proportional to the amine concentration at equilibrium conditions, so with the increase in the concentration of EDA in the liquid solution, there was a corresponding increase in the CO2 solubility and, subsequently, the EDA–CO2 chemical reaction took place, increasing the CO2 loading.”
Table 2. CO2 capture using EDA: Kinetic and thermodynamic data.
Kinetic Data Thermodynamic Data
EDA Conc. (wt.%) dn/dt
CO2 Removed (mmol) CO2 Loading (*)
(mmol CO2 /mol Liquid)
0 0.654 2.20 23.31 145.30 3007 21.25 12.82
5 0.974 4.35 24.23 155.11 2450 41.63 26.03
10 1.040 5.28 27.28 172.16 2195 51.81 33.66
20 0.859 11.55 44.56 255.91 1640 69.72 49.03
(*) Initial moles of liquid: see Appendix A.

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