Monoethanolamine Degradation Rates in Post-combustion CO2 Capture Plants with the Capture of 100% of the Added CO2

Residual emissions from post-combustion CO2 capture plants must be reduced to zero or recaptured from the atmosphere to be compatible with long-term climate change goals. For amine-based CO2 capture, increasing CO2 capture fractions requires maintaining sufficient driving force of absorption at the top of the absorber column by reducing lean solvent loadings. To produce low lean loadings without excessively increasing the specific thermal energy input, increased operational pressures are required in the CO2 stripper, inevitably leading to higher temperatures, which may increase the specific thermal degradation rate of the solvent. Concurrently, for solvents that react rapidly with dissolved O2, increased residence time in the absorber due to the increased packing heights also associated with high capture fractions may increase the specific oxidative degradation rate as the direct contact with O2 in the flue gas is extended. Through process modeling and the application of a newly developed monoethanolamine (MEA) degradation framework, we investigate the effect on solvent degradation rates of increasing CO2 capture rates up to those that result in no net CO2 addition to the atmosphere. We do this for three key energy-producing processes: a combined cycle gas turbine, an energy from waste facility, and a steam methane reformer. In a first-of-a-kind study, we demonstrate that for a 35 wt % MEA-based solvent under steady-state conditions, solvent degradation is predicted to increase by 24–138% as a result of decreasing lean loadings and increased absorber residence time (process modifications that are thought to be beneficial when increasing CO2 capture fractions) from 53 to 208 gMEA/tCO2 when a 95% CO2 gross capture fraction is achieved to 125–257 gMEA/tCO2 when 99.2–99.8% is achieved (i.e., when 100% of the added CO2 is captured). Further analysis provides evidence that process modifications, such as intercooling of the absorber column and reduced stripper sump residence times, may be useful in reducing the rates of solvent degradation, providing critical insights to future test campaigns and project developments. However, limitations of this study remain; the degradation framework provides the instantaneous predicted MEA consumption rate of the system at a point in time and does not consider the catalytic effects that many impurities present in an operation plant will have on the reactions, potentially impacting degradation rates. Nonetheless, this serves as the first step toward understanding the effect of increasing CO2 capture fractions in post-combustion CO2 capture plants. Long-term tests with appropriate solvent management practices are required to fully quantify solvent degradation rates when operating at 100% added CO2 capture fractions.