Carbon dioxide capture in 2,2'-iminodiethanol aqueous solution from ab initio molecular dynamics simulations.

The reaction of carbon dioxide (CO2 ) with aqueous 2,2'-iminodiethanol (trivial name is diethanolamine: DEA) has been investigated using both blue moon ensemble and metadynamics approaches combined with ab initio molecular dynamics (AIMD) simulations. A spontaneous direct proton transfer from DEA zwitterion (DEAZW) to DEA but not to H2 O has been observed in straightforward AIMD simulation in the time scale of ps. The ab initio free-energy calculations reproduced the overall free-energy difference, predicting the ionic products DEA carbamate ion (DEAC) and the protonated DEA (DEAH). The computed free-energy barrier for the first reaction step, which is the CO2 binding (48 kJ mol-1 ), is found to agree reasonably well with the available experimental data (52-56 kJ mol-1 ). By contrast, the barriers for the next step, the deprotonation of zwitterion realized either via reaction with DEA or H2 O, are underestimated by 25-35 kJ mol-1 compared to the experimental reference. A part of this error is attributed to the neglected reversible work needed to bring two reactants together, which might significantly contribute to the free-energy of activation of bimolecular reactions in a dilute solution. The computed free-energy profile is compared with our results [Y. Kubota et al. , J. Chem. Phys. 146 , 094303 (2017)] for the same reaction in 2-aminoethanol (trivial name is monoethanolamine: MEA).