Atmospheric chemical reactions of monoethanolamine initiated by OH radical: Mechanistic and kinetic study

Monoethanolamine (MEA) is a benchmark and widely utilized solvent in amine-based postcombustion CO₂ capture (PCCC), a leading technology for reducing CO₂ emission from fossil fuel power plants. The large-scale implementation of PCCC would lead to inevitable discharges of amines to the atmosphere. Therefore, understanding the kinetics and mechanisms of the transformation of representative amine MEA in the atmosphere is of great significance for risk assessment of the amine-based PCCC. In this study, the H-abstraction reaction of MEA with ·OH, and ensuing reactions of produced MEA-radicals, including isomerization, dissociation, and bimolecular reaction MEA-radicals+O₂, were investigated by quantum chemical calculation [M06-2X/aug-cc-pVTZ//M06-2X/6-311++G(d,p)] and kinetic modeling. The calculated overall rate constant [(7.27 × 10^-11) cm³ molecule^-1 s^-1] for H-abstraction is in excellent agreement with the experimental value [(7.02 ± 0.46) × 10 ^-11 cm³ molecule^-1 s^-1]. The results show that the product branching ratio of NH₂CH₂· CHOH (MEA-β) (43%) is higher than that of NH₂·CHCH ₂OH (MEA-α) (39%), clarifying that MEA-α is not an exclusive product. On the basis of the unveiled reaction mechanisms of MEA-radicals + O₂, the proton transfer reaction mass spectrometry signal (m/z 60.044), not recognized in the experiment, was identified.