Monoethanolamine (MEA) is a benchmark and widely utilized solvent in amine-based post-combustion 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 Cl radicals, and ensuing reactions of produced MEA-radicals, including isomerization, dissociation and bimolecular reaction MEA-radicals+O2/NO, were investigated by quantum chemical calculation and kinetic modeling. For the OH initiated reaction, 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 product branching ratio of NH2CH2CHOH (MEA-β) (43%) is higher than that of NH2CHCH2OH (MEA-α) (39%), clarifying that MEA-α is not an exclusive product. However, the calculated overall rate constant [(3.6×10-10) cm3molecule-1s-1] for H-abstractions initiated by Cl is about 5 times faster than that of corresponding reaction initiated by OH radicals. Importantly, the reaction of MEA+Cl exclusively produces N-center radical (MEA-N), which is different from the reaction initiated by OH. Main products MEA-β and MEA-N finally leads to the formation of amino acetaldehyde and carcinogenic nitrosamine by its further reaction with O2/NO. Based on 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.

Computational study on atmospheric transformation of monoethanolamine

256th National Meeting (2018)

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