Oxidative degradation experiments using MEA

“2.2.1. Setup 1 (three parallel reactors)

Oxidative degradation experiments were performed at absorber conditions in custom made open, water bath-heated, double-jacketed glass reactors (approximately 250 mL) as shown in Fig. 1. The reactor temperature was maintained at 60 °C and the water bath-cooled Graham condensers at 5 °C. Each reactor was filled with 200 mL of the gravimetrically prepared solvent mixture, which was pre-loaded to 0.4 mol of CO2 per mol MEA and contained 0.5 mM iron sulfate (FeSO4·7H2O). A mixture of 98% oxygen (O2) and 2% carbon dioxide (CO2) gas was sparged through the solutions at a rate of 60 mL min−1 from Alicat mass flow controllers and through Pyrex® glass gas distribution tubes of porosity grade 1, under constant magnetic stirring for the total experimental time of three-six weeks. Empty gas wash bottles were used as safety solvent traps between the mass flow controllers and the gas distribution tubes in case of power outage. Sampling was performed on days 3, 7, 10, 14 and 17 (as well as 21, 28 and 35 for the six-week experiment), through a septum on top of each reactor. Each experiment was performed in two or three parallels, and the data presented in this work is given as the average values, with the standard deviation of the sample average as uncertainty. Experiments were primarily conducted in Setup 1, but validation was done with Setup 2, against published data for MEA stability.”


Fig. 1. Schematic of oxidative degradation Setup 1.”

“2.2.2. Setup 2 (single reactor)

1 L 30 %wt. MEA (aq.) with 2.0 %wt. KI, preloaded with 0.4 molCO2 molMEA−1 and FeSO4 (1 mM), was added to an open batch setup described in Vevelstad et al. (2016). The setup belongs to SINTEF Industry and consists of a double-jacketed, water-bath heated glass reactor, kept at 55 °C, with a double water-cooled Graham condenser, continuous magnetic stirring and sparging with water-saturated gas (98% O2; 0.350 L min-1 and 2% CO2; 7.5 mL min-1). A recycle gas stream (50 L h-1) is bubbled through the solution for increased mass transfer from gas to liquid phase. This is precisely the same apparatus employed by Vevelstad et al. (2016). The experiment was performed for three weeks with regular sampling and the results were compared to that of 30 %wt MEA without addition of iron as given in Vevelstad et al. (2016).

2.2.3. Thermal degradation experiments

Thermal degradation experiments were performed in accordance with Eide-Haugmo et al. (2011) in stainless steel 316 cylinders with diameters of 0.5 in. and volumes of approximately 11 mL equipped with Swagelok® end caps. The cylinders were filled with 8 mL of the solution, which was pre-loaded to 0.4 molCO2 molMEA−1 and kept at 135 °C for up to five weeks. Each sampling involved the removal of two metal cylinders per experiment and the analyses of their contents, meaning that the sample taken after three weeks was kept uninterruptedly at 135 °C for three weeks, etc. The cylinders were weighed on a Mettler-Toledo ME204 analytical scale (taring range 0–220 g and readability 0.0001 g) prior to the filling with solution, as well as after the sample was removed, before and after the cylinders were washed with sulfuric acid (H2SO4, 0.1 M) to remove iron carbamate (FeCO3) and other corrosion products from the stainless steel surface. The solutions were analyzed for amine concentration by titration, and CO2 loading was verified by TIC procedures and sent for ICP-MS analysis.”

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