Steered rare event and classical MD combined with quantum DFT for multiscale mechanistic modeling of CO2 capture by amine-based solvents

SF Rafie and M Tamtaji and M Rahimi and PRT Nunna and N Abu-Zahra, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 13, 119470 (2025).

DOI: 10.1016/j.jece.2025.119470

A three-tier multiscale model combining density functional theory (DFT), classical molecular dynamics (MD), and steered rare-event sampling (COLVARS) is presented to investigate CO2 capture in 26 wt% aqueous monoethanolamine (MEA) at 327.15 K, linking electronic interactions with molecular transport. Classical MD reveals a two-stage capture pathway, beginning with rapid interfacial accomodation followed by slower absorption and diffusion into the bulk. The bulk translational self- diffusion coefficient of CO2 is 2.62 x 10-9 m2/s. Structural and energetic analyses show that CO2 preferentially associates with amine groups. In contrast, steered rare-event MD resolves the orientation- dependent approach of CO2 to MEA along a single collective coordinate and yields an effective one-dimensional diffusivity of 8.46 x 10-11 m2/s, which is two orders of magnitude lower than the bulk value. This lower value reflects the constrained, energetically hindered association step, not the free diffusion in solution, and reveals a kinetic bottleneck before chemical binding. Complementary DFT-D3 calculations confirm stronger binding to the NH2 group (-0.37 eV) than to the OH group (-0.25 eV), with proton-transfer intermediates reaching-0.67 eV. Applying a 0.1 eV external electric field weakens the interaction and reduces charge transfer from 0.49 e to 0.41 e, suggesting a strategy for lowering the energy required for solvent regeneration. By combining classical MD, biased dynamics, and electronic-structure calculations, this multiscale framework offers a clear picture of how solvent organization and molecular mobility work together to drive CO2 capture in MEA-water solutions.

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