Fundamental studies of carbon capture at the molecular scale

Despite its necessity for terrestrial life, CO₂ or rather the quantity of atmospheric CO₂ has received considerable attention over recent years and not for positive reasons. Elevated atmospheric CO₂ levels are responsible for climate change, with most people now firmly aware that the hazards and consequences posed by climate change can no longer be ignored. Whilst a global switch to renewable energy generation is an essential pillar for sustainable development, it is not possible to undertake this switch within the current timescale required. The use of carbon capture and storage technologies facilitates this energy-switch by reducing CO₂ emissions from both power generation and manufacturing processes. Beginning with a review of the more fundamental chemistry of CO₂ followed by outlining the chemical process underlying carbon capture techniques provides a suitable foundation to present the research documented within this thesis. Solvent dependent pKa values are first examined with a method to measure pKa in mixed aqueous organic solvent systems initially presented with this technique herein utilised to measure some pKa values of carbon capture-relevant acids in a variety of solvent systems. Following this, a thermodynamic model is presented in an attempt to understand the curious trends in how pKa varies with solvent composition observed in this work. A full derivation of a solvation model is presented alongside an experimental outline of how this model may be empirically confirmed. It is shown that the inflection point of a pKa vs. solvent composition plot sits at the same position of the maximum of a preferential solvation vs. solvent composition plot, indicating an intimate link between solvation and pKa. Determining the total CO₂ loading of a carbon capture solution at a given point is an essential metric in understanding the performance of said solution. To this end, a novel technique using fluorescence spectroscopy was proposed. This involved the synthesis of a number of fluorescent compounds, some of which have not been reported in the wider literature, and subsequently testing their fluorescence response to CO₂ loading in a model carbon capture solvent – with promising results. Finally, solutions of sodium and potassium glycinate were probed using neutron diffraction techniques to understand how the molecular geometry and association of the constituent components of carbon capture solutions change upon absorbing CO₂. The results and enthalpic values obtained are then used to understand solution-state behaviour of capture solutions on a molecular level. The conclusions and understandings derived from this work have significant implications for the intelligent design and implementation of carbon capture and storage technologies.