Fundamental Chemistry of Carbon Dioxide Capture

Carbon dioxide capture is an urgently needed pathway to mitigation of climate change, yet the amine-based solvents currently considered the leading industrial technologies suffer from many shortcomings; namely their high operating cost, poor stability and potentially damaging environmental impact from emission of degradation products. This work is a study of possible routes to improved CO2 capture technologies from a fundamental chemistry perspective.
Initial work focused on the development of a straightforward and adaptable protocol for studying the species formed by CO2 capture into amine solvents, using 1H NMR spectroscopy for its combination of speed and accuracy. The applicability of this approach to diverse blended-amine solvents was demonstrated.
This method was then applied to the study of phenoxide as a novel possible capture agent in conjunction with amines. Blends of potassium phenoxide with monoethanolamine were found to have an excellent capture capacity and favourable speciation that suggests a low energy consumption in practical use. This demonstrates the feasibility of blended solvents with a reduced amine component.
Finally, a possible amine-free route to CO2 capture, exploiting the high susceptibility of carboxylate acidity to solvation, was explored. The first systematic study of the pKa of CO2 in mixtures of organic solvent and water was carried out, finding that this value is relatively insensitive to the makeup of the solvent and therefore in organic-rich solutions, carboxylate salts can be used as a CO2-absorbing base. CO2 capture using a system developed along these principles was demonstrated, and the possible basis for the observed insensitivity was discussed with particular emphasis given to the thermodynamics of the process.