https://doi.org/10.1021/acs.energyfuels.0c00880
“The integral heat of absorption of NMP + DEEA 10 wt % at 40 °C shown in Figure 7 is also comparable to that of physical solvents (ΔH ≈ 15 kJ·mol CO2–1).”
“Figure 7. Integral heat of absorption data for solvents containing 10 wt % N,N-diethylethanolamine.”
“On the other hand, MEG + DEEA 10 wt % again shows a typical chemical absorption profile at both 40 and 80 °C, and its heat of absorption shown in Figure 7 supports the assumption of a reactive fixation of CO2 (ΔH ≈ 58–60 kJ·mol CO2–1, typical of tertiary amines (48)).
“It has been a point of contention in the last decades whether chemical absorption of CO2 can happen with tertiary amines in nonaqueous solvents or not. While many authors support that there is no direct reaction between the amine and CO2 itself and suggest that water is needed for the conversion to take place, (56−58) others propose an alkylcarbonate mechanism where the tertiary amine can react with CO2 even in the absence of water. (6,59) In recent years, NMR spectroscopy has shown that alkylcarbonates are indeed formed upon absorption with tertiary amines, validating the latter point of view. (60,61) Still, the depression of the reactive absorption of CO2 when shifting from aqueous to nonaqueous tertiary amine solvents has been experimentally observed to be strong enough to support both viewpoints. Conversely, to the best of our knowledge, the absorption profiles shown in Figure 6 are the strongest VLE examples of a tertiary amine behaving in a nonaqueous solvent as closely as it would in pure water, with a singularly small loss of capacity compared to aqueous DEEA.