Different amine modified MCM-41 for CO2 capture

https://doi.org/10.1093/ce/zkac020

“Fig. 6 shows the breakthrough curve of MCM-41 and amine-modified MCM-41 adsorbents. The C_ou/C_in indicates the continuous increase in the CO₂ concentrations of the effluent, which gradually reaches 1.0 when the adsorbent is saturated with CO₂. The CO₂ adsorption capacity (Q_ads) of the adsorbents was obtained by integrating the area of the breakthrough profile and further calculated using Equations (5) and (6) [76]. As seen in the breakthrough curve of unimpregnated MCM-41, no breakthrough time was observed and the Q_ads was 0.63 mmolCO₂/g, contributing to the physisorption mechanism. When MCM-41 was impregnated with EAE, EDA and TEPA, their breakthrough times were delayed and the total CO₂ uptake was increased. EAE/MCM41 showed breakthrough times of 2.65, 7.72 and 9.85 minutes with Q_ads of 3.34, 3.84 and 4.52 mmolCO₂/g for 30, 50 and 60 wt% EAE. The breakthrough points of EDA/MCM-41 were increased to 0.52, 0.52 and 7.72 minutes for 30, 50 and 60 wt% EDA/MCM-41 with Q_ads of 0.95, 1.23 and 3.20 mmolCO₂/g, respectively. TEPA/MCM-41 showed breakthrough times of 0.52, 5.58 and 5.58 minutes with Q_ads of 0.99, 2.13 and 3.30 mmolCO₂/g for 30, 50 and 60 wt% TEPA/MCM-41, respectively (see Table 2). The Q_ads was enhanced due to the strong chemical interaction between CO₂ and the amine functional group existing in the MCM-41 even though the surface area of the MCM-41 was reduced. It indicated that the strong chemical reaction is more dominant than the physisorption process [32]. The results showed that EAE/MCM-41 had the highest Q_ads among others. EAE is a secondary alkanolamine with one ethyl group and one ethyl alcohol group attached to the nitrogen atom. The presence of the ethyl group increases the basicity of the amine as a property of an electron-donating group that can provide an electron density to the nitrogen [66]. The amines’ basicity was 10.12 for EAE, which was higher than that of EDA (pKa = 9.99) and TEPA (pKa = 8.91). Multi-alkylamines could form intramolecular hydrogen bonding, decreasing their amine groups’ basicity [77]. In addition, the Q_ads was also increased with increasing amine loading. The enhancement of Q_ads as the amine concentration increased was obtained due to the higher affinity of amine sites for CO₂. At lower amine loading, the Q_ads might be obtained from physical and chemical adsorption. When the pore channels of MCM-41 were filled with ~60 wt% loading, the chemisorption became dominant [32].”