Carbon capture is a key yet cost-intensive technology for the fight against climate change. Among carbon capture processes, we are encouraged by the single-component water-lean solvent, N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA, E), as it has the highest solvent energy efficiency (2.0 GJ/tonne CO₂) and lowest costs of capture ($39/tonne CO₂) of any CO₂ capture technology in the literature. But it is not clear how these performance metrics arise. Here, we detail a combined experimental and modelling study of to learn the molecular-level underpinnings of EEMPA, specifically on learning how its molecular-level properties impact macroscale phenomena. In this study we present evidence that CO₂ capture by EEMPA is accompanied by a self-assembly of reverse micelle-like tetrameric clusters in solution. This results into stepwise negatively cooperative capture with highly contrasting kinetic and thermodynamic features that were previously thought implausible in liquid sorbents. The tetrameric clusters act like nano-sized micelles that solvate CO₂-containing ions within the core, enabling a tetrameric binding mechanism of CO₂ fixation. This unusual charge solvation explains EEMPA’s low viscosity and poor conductivity but also contradicts our previous efforts to design a water-lean solvent yielding intramolecularly H-bonded carbamic acid upon capture. We also detail how these well-defined supramolecular architectures display an internal core that is reminiscent of enzymatic active sites, which provide a unique hydrogen-bonding environment promoting formation and stabilization of CO₂-containing molecular species such as carbamates, carbamic acid, and unprecedented carbamic-anhydrides, a species with two CO_z molecules bound in linear fashion. In this talk, we detail the discovery and thermodynamics of this tetrameric binding mechanism, supported by detailed experimental measurements. Theoretical calculations confirm our model and illustrate the dynamic changes of these tetrameric clusters during binding and release of CO₂. We conclude with discussions of how these newly discovered structures enable the design of future solvents that could exhibit cooperative binding like hemoglobin. Similarly, we detail how the active-sites discovered here provide a roadmap for how amine-based materials could be designed to double their CO₂ storage capacity by activating carbamates and CO₂ within, enabling oligomerization or polymerization of CO₂in the future.

Marc Hennebelle

Appearances