Reactive Uptake of Monoethanolamine by Sulfuric Acid Particles and Hygroscopicity of Monoethanolaminium Salts

CO₂ capture plants are a significant source of emission of monoethanolamine (MEA) in the atmosphere. As a potential MEA sink, the heterogeneous uptake of MEA by sulfuric acid (SA) particles can form particulate MEA sulfate (MEAS), changing the hygroscopicity of the particles. We determined the hygroscopicities of MEA salts, including MEAS, at different MEA:sulfate molar ratios over a wide range of relative humidity (RH) using an electrodynamic balance (EDB) and a water activity meter. Other salts, including MEA oxalate, nitrate, and chloride, were studied using the water activity meter. Empirical functions were fitted to the experimentally measured hygroscopicity data of MEA salts. We further investigated the reactive uptake of parts per million-level MEA by SA particles in an EDB. The relative mass change of the levitated particles was the combined result of MEA uptake and changes in particle hygroscopicity due to compositional changes. The measured hygroscopicity was used to analyze the particle composition change during MEA uptake and the uptake kinetics. The uptake coefficients (γ_MEA) were estimated to be (3.23 ± 0.64) × 10^-3 and (9.89 ± 2.62) × 10^-4 at 40% and 70% RH, respectively. MEA reactive uptake by acidic particles could be competitive with respect to MEA gas-phase oxidation under high-particle concentration conditions near power plants.