Oxidative stability of monoethanolamine in CO2 capture using dissolved oxygen measurements
Yamid Gomez-Rueda (TNO)
Melvin Kruijne (TNO)
Daphné Cette (TU Delft - RST/Reactor Physics and Nuclear Materials)
Ankit Sinha (Student TU Delft)
Juliana Monteiro (TNO)
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Abstract
Post-combustion carbon capture using amine-based solvents faces challenges like oxidative degradation. O₂ is a ubiquitous component in flue gases and induces irreversible oxidation reactions in the amines, reducing CO₂ capture efficiency and increasing corrosion and maintenance costs. This study proposes monitoring dissolved O₂ (DO) to estimate the solvent oxidation behaviour, avoiding complex chromatographic methods. The approach assumes that oxygen is exclusively consumed by the initial amine during the oxidation process, linking the oxygen depletion kinetics with the amine-oxidation kinetics. DO measurements in monoethanolamine (MEA) reveal significant insights into the kinetics of the oxidative degradation process. CO₂ presence, investigated across different temperatures, accelerates O₂ depletion compared to unloaded samples, though there is no clear correlation between the amount of CO₂ loading and O₂ depletion rates. Making MEA more acidic accelerates oxygen depletion rates; still, the change in pH alone is unable to reproduce the DO rates observed in CO2-loaded MEA. Higher temperatures accelerate the MEA oxidation. Metal contamination through iron sulphate and iron nitrate accelerates O₂ consumption rates, with the amount of iron being more relevant than the oxidation state of the iron in the original salt or the salt counterion. The influence of viscosity and chelators was studied by adding glycerol and chelating agents as additives, but the results were challenging to interpret. Initial measurements of MEA-Water-glycerol and MEA-Fe-chelating agent mixtures unexpectedly accelerate O₂ consumption, challenging assumptions about the glycerol's role as a non-reactive solvent and chelating agents as oxidation inhibitors. It is revealed through blank experiments that glycerol also oxidises in MEA mixtures, breaking the link between DO decay and MEA consumption, while the tested iron complexes act rather as oxidation catalysts.
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