Oxidative degradation of aqueous monoethanolamine in carbon dioxide capture processes: Iron and copper catalysis, inhibition, and oxygen mass transfer

Oxidative degradation of monoethanolamine (MEA) was quantified by measuring NH3 evolution using FT-IR analysis. This study used a sparged and an agitated reactor, controlled to within +/-1°C. The rate of NH 3 evolution was quantified at 55°C, representative of absorber conditions in a typical MEA absorption stripping process for CO2 removal from flue gas. The effect of important process parameters, Fe/Cu/MEA/O2 concentrations, CO2 loading, pH, and agitation was studied. NH 3 evolution rates ranged from 0.15--8.7 x 10-3 mo/L-hr.; Under significant experimental and industrial conditions, the rate of NH3 evolution is controlled by the rate of O2 absorption. Under some experimental conditions the rate of NH3 evolution depends only on kinetics, and under other conditions the rate depends on both kinetics and O2 mass transfer. NH3 evolution rates increased with agitation and increased linearly with O2 concentration. With low catalyst (below 0.5 mM Fe/Cu) and MEA (less than 2.0 molal), NH3 evolution was controlled by kinetics. With high catalyst (above 0.5 mM Fe/Cu) and MEA (above 7.0 molal), NH3 evolution was controlled by the rate of O2 mass transfer. Solutions between 2.0 and 7.0 m MEA showed effects of both O2 mass transfer and degradation kinetics.; Previously reported degradation studies reported lower degradation rates under lower O2 mass transfer conditions, indicating that these studies were also O2 mass transfer limited. Industrial degradation rates were predicted for CO2 capture from flue gas assuming degradation was limited by the rate of O2 absorption. Results under-predict rates reported in the literature, indicating that in industrial applications oxidative degradation of MEA is likely controlled by the rate of O2 absorption.; Chelating agents, stable salts, O2 scavengers and reaction inhibitors, were tested as possible inhibitors. Only O2 scavengers and reaction inhibitors show enough reduction in NH3 evolution rates to be considered viable additives in an industrial application. Inhibitor A, a reaction inhibitor, is a stable inorganic compound. Na2SO 3 and formaldehyde are both O2 scavengers and are consumed stoichiometrically at the rate of O2 mass transfer. All three inhibitors are more effective at reducing Cu catalyzed degradation and effectively reduce oxidative degradation at concentrations of approximately 100 to 250 mM.