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Aqueous monoethanolamine (MEA) at concentrations of 5 and 7 M was degraded with 100 mL/min of 98% O 2 /2% CO 2 (98 mL/min O 2 ), with oxygen mass transfer achieved by vortexing in a low-gas-flow degradation apparatus. Degraded samples were analyzed by ion chromatography (IC) and high-pressure liquid chromatography (HPLC) with evaporative light scattering detection (ELSD) for oxidative degradation products. In a high-gas-flow apparatus, 7.5 L/min of 83% N 2 /15% O 2 /2% CO 2 (1125 mL/min O 2 ) was sparged through a mechanically agitated 5 M MEA solution. A Fourier transform infrared (FTIR) analyzer collected continuous gas-phase data. Formate (HCOO − ), hydroxyethyl formamide (HEF), and hydroxyethyl imidazole (HEI) account for 92% of degraded carbon at low-gas-flow conditions and 18−59% of degraded carbon at high-gas-flow conditions. Oxalate (C 2 O 4 2− ), oxamide (C 2 H 4 N 2 O 2 ), glycolate (HOCH 2 COO − ), acetate (CH 3 COO − ), carbon monoxide (CO), ethylene (C 2 H 4 ), formaldehyde (CH 2 O), and acetaldehyde (CH 3 CHO) are oxidation products in lower concentrations. Ammonia (NH 3 ), HEF, and HEI account for 84% of degraded nitrogen at low-gas-flow conditions and 83−92% at high-gas-flow conditions. Nitrogen oxides (NO x ), present in lower concentrations, are stripped from solution at high-gas-flow conditions and retained in the degraded solution at low-gas-flow conditions and oxidized to nitrite/nitrate (NO 2 − /NO 3 − ). A comparison of product rates to MEA losses shows that 25−50% of products remain unaccounted for in unknown HPLC peaks. Oxygen consumption rates vary from 1 to 2 mM/h, whereas the overall oxygen stoichiometry is 0.75 mol of O 2 /mol of MEA degraded.
Sexton et al. (Tue,) studied this question.