Optimisation de la gestion des solvants pour réduire l'empreinte environnementale du processus de capture du CO2 – SolveMORE

Solvent-based CO2 capture (absorption) is currently the leading technology for CO2 capture, with most vendors offering solvent technology primarily based on amines. However, an inherent challenge with amine solvents, being organic molecules, is their susceptibility to degradation during the capture process. When the solvent degrades, it loses its capacity to capture CO2, necessitating the addition of make-up solvent. For the CESAR1 solvent, this corresponds to approximately 0.6 kg of amine per ton of CO2 captured, adding a cost of about 10-20 €/tCO2. The degradation process also produces compounds that have unfavorable properties, which increases safety and environmental risks during operation.

As a result, there is considerable interest in improved solvent management technologies designed to extend the solvent's lifetime, ensure smooth and risk-free operations, reduce costly maintenance, and increase plant availability. The term “solvent management” encompasses any strategy aimed at prolonging solvent life and minimizing operational risks and costs by maintaining the solvent over extended periods of operation.

However, solvent management is not yet fully explored and understood for post-combustion capture (PCC) processes involving liquid amine solvents. Many of the techniques currently used in the PCC context are adapted from the natural gas processing industry, which operates under significantly different conditions. There is a lack of understanding of how various solvent management strategies, such as the common practice of thermal reclaiming, affect solvent chemistry and, consequently, the rate of solvent degradation and the quality of the CO2 product. Additionally, solvent management operations, like reclamation, often lead to significant losses of amine solvent, generating large amounts of unnecessary solvent waste.

Advancements in this area will help lower the costs associated with CO2 capture deployment. Developing sound recommendations for solvent management strategies will diminish the uncertainties linked to operational costs, including waste stream treatment. A more stable solvent with reduced degradation will also decrease the risk of harmful and unwanted emissions, thus minimizing the environmental impact of the capture process.

A unique 34,000-hour test campaign examining the degradation behavior of the CESAR1 solvent and the effect of solvent management technologies at the capture pilot plant in Niederaussem has revealed that a common hypothesis about amine degradation is incorrect. Specifically, this finding challenges the traditional mantra of “keeping the solvent clean” to minimize solvent consumption. Recent research, including the article "Degradation Behaviour of Fresh and Pre-Used Ethanolamine" by Buvik et al. (2023), aligns with earlier studies at both laboratory and pilot scales on the benchmark solvent, monoethanolamine (MEA), confirming that a slightly degraded solvent can be more stable than a fresh one.

An important takeaway from this research is that aging the solvent may positively affect its stability, suggesting that some compounds that accumulate during operation could enhance solvent lifetime and should not necessarily be removed. This finding contradicts established solvent management strategies that typically aim to eliminate any contaminants from the solution. Tests involving solvent treatment with anionic and cationic exchange resins have demonstrated that metal ions, which can catalyze solvent degradation, are partially complexed by anions. Depending on the bond strength between the ligands in the solvent matrix and the metal cations, their catalytic activity for solvent degradation is influenced. Accordingly, SolveMORE aims to further reduce the formation and accumulation of degradation products by maximizing and utilizing self-protecting mechanisms against degradation while minimizing the effort required for solvent management.