Off-gas emission in CO2 capture process using aqueous monoethanolamine solution

A comprehensive study was conducted to evaluate roles of O2, SO2 (i.e. H2SO3), NO2 (i.e. HNO3), CO2 and temperature to off-gas emissions using conditions normally encountered in the CO2 capture process. Two possible pathways of radical induced oxidation of MEA in the presence/absence of H2SO3, HNO3, and CO2 were proposed to explain the release of NH3 as a major VOCs emission. In the presence of H2SO3, HNO3, and CO2, an increase of their concentrations decreased NH3 concentration, while the rest of VOCs (i.e. acetaldehyde, acetone, diethylamine, 2-butanol, methyl dl-lactate, methanol and ethanol) were found to be insignificantly affected. An increase of temperature was found to increase the concentration of all VOCs detected in this study. Based on mechanism analysis, the roles of H2SO3, HNO3, and CO2 were found to be that of cutting down the route to NH3 formation and instead induced the formation of formate and acetate heat stable salts in MEA solution. Additional liquid MEA analysis revealed that most NH3 was actually trapped and turned into NH4+ salts in MEA solution before it could be emitted as NH3 in the off-gas.