Influence of Dissolved Metals and Oxidative Degradation Inhibitors on the Oxidative and Thermal Degradation of Monoethanolamine in Postcombustion CO2 Capture

In the present work, the influence of metal ions and oxidative degradation inhibitors on the stability of monoethanolamine solvents (MEA) is studied. Solvent degradation induces additional costs and impacts the environmental balance of the CO2 capture process as well as its efficiency. The two main degradation pathways of MEA are studied under accelerated conditions: oxidative degradation with continuous gas feed and thermal degradation in batch reactors. It is confirmed that metal ions (resulting from solvent impurities and wall leaching) enhance the oxidative degradation of MEA, while they do not impact its thermal degradation. Moreover, different oxidative degradation inhibitors are tested with varying results according to the inhibitor. It appears that at the selected concentration, radical scavengers like Inhibitor A and DMTD (2,5-dimercapto-1,3,4-thiadiazole) are more efficient than chelating agents like HEDP (1-hydroxyethylidene diphosphonic acid) at inhibiting oxidative degradation. Furthermore, attention must be paid to the influence of oxidative degradation inhibitors on the thermal degradation of MEA. Indeed, some inhibitors like DMTD, DTPA (diethylenetriaminepentaacetic acid), and DTDP (3,3'-dithiodipropionic acid) appeared to decrease the MEA thermal stability, which cannot be accepted in industrial applications. Finally, a further drawback of DTPA is its high affinity for metal ions, leading to a more corrosive solution, so its use is not recommended for CO2 capture applications.