Reaction Products from the Oxidative Degradation of Monoethanolamine

Abstract

Aqueous monoethanolamine (MEA) at concentrations of 5 and 7 M was degraded with 100 mL/min of 98% O2/2% CO2 (98 mL/min O2), 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% N2/15% O2/2% CO2 (1125 mL/min O2) 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 (C2O4 2−), oxamide (C2H4N2O2), glycolate (HOCH2COO−), acetate (CH3COO−), carbon monoxide (CO), ethylene (C2H4), formaldehyde (CH2O), and acetaldehyde (CH3CHO) are oxidation products in lower concentrations. Ammonia (NH3), 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 (NO2 −/NO3 −). 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 O2/mol of MEA degraded.

Oxidative degradation of 2-ethanolamine: The effect of oxygen concentration and temperature on product formation

“…At 55 o C there seems to be an almost linear relationship between oxygen content ( Figure 14) and HEI formation whereas at 75 o C the curve seems to follow the behaviour of HEPO, a steeper slope the first 12 days and then levelling off (see Figure 12). All of the compounds which Ben (Ben 2005) used to synthesise HEI have been reported as degradation compounds from MEA by several research groups (Gouedard et al, 2012;Sexton and Rochelle, 2011). Literature also reports that the syntheses of different imidazoles take place around 60 or 70-90 °C (Ben, 2005;Prasanthi et al, 2007).…”

“…Lately there has been increased focus on the effect of temperature swing under industrial operation and an integrated solvent degradation apparatus (ISDA) was developed where the solvent is exposed to both oxidative and thermal degradation conditions in a single system (Closmann and Rochelle, 2011). Over the years several oxidative degradation experiments were performed by researchers studying different aspects of degradation like overall degradation rate (Blachly and Ravner, 1966;Chi and Rochelle, 2002), degradation products formed (da Silva et al, 2012;Lepaumier et al, 2009;Sexton and Rochelle, 2011;Supap et al, 2006), stability of the amines (Kohl and Nielsen, 1997;Lepaumier et al, 2009;Rooney et al, 1998) and the effects of oxidation catalyst (Goff and Rochelle, 2006), CO2 loading (Bello and Idem, 2006;Chi and Rochelle, 2002;Lawal et al, 2005;Rooney et al, 1998;Supap et al, 2009;Uyanga and Idem, 2007), inhibitors (Chi and Rochelle, 2002;Goff and Rochelle, 2006), amine and oxygen concentration (Bello and Idem, 2006;Goff and Rochelle, 2004;Supap et al, 2009;Uyanga and Idem, 2007), agitation rate (Goff and Rochelle, 2004), temperature (Bello and Idem, 2006;Lawal et al, 2005;Supap et al, 2009;Supap et al, 2001). The overall degradation rate was often determined by monitoring the evolution of NH3 (Chi and Rochelle, 2002) or a combination of NH3 and peroxide (Blachly and Ravner, 1966).…”

Oxidative degradation of amines using a closed batch system

“…Using Sexton's (Sexton and Rochelle, 2011) suggested oxygen stoichiometry, as explained earlier, for formic acid, HEI, HEF HNO2, oxalic acid and HNO3 would consume about 97 mmoles of O2 for the first MEA experiment in the closed setup. Calculating O2 present for the system resulted in 30 mmoles O2 available at start-up (gas volume 4L).…”

“…In the cases where there is oxygen consumption by degradation, the partial pressures of oxygen can be explained by the combination of re-entry of oxygen due to diffusion and consumption through the degradation reactions. This latter contribution can be calculated according to Sexton (Sexton and Rochelle, 2011) where oxygen consumption was estimated from the reaction between MEA and oxygen resulting in ammonia and the chosen degradation compounds. When both mechanisms are taken into consideration, it is possible to show that the oxygen consumption prediction is in reasonable agreement with the observed profiles.…”

“…Increased attention on oxidative degradation was seen after pilot plant samples showed high degree of similarity to degradation compounds found in oxidative degradation experiments (da Silva et al, 2012;Lepaumier et al, 2011a;Strazisar et al, 2003). The oxidative degradation experiments reported have been performed in variations of two setups, either in a closed-batch reactor at elevated temperature and oxygen pressure (Lepaumier et al, 2009b;Supap et al, 2001;Wang and Jens, 2011) or in an open-batch reactor at 55 °C, where the solution would be sparged with a wet gas blend of CO2 and O2/air (da Silva et al, 2012;Goff and Rochelle, 2004;Lepaumier et al, 2011b;Sexton and Rochelle, 2011). Lately, also the temperature swing The present paper describes results from oxidative degradation experiments on five amines and two amino acids in a laboratory scale closed setup at atmospheric pressure.…”