This thesis proposes a potentially new approach to seawater desalination using CO2 and nucleophilic diamines, as opposed to conventional membrane-based desalination technologies (which enable potable drinking water via a size-based salt rejection approach). Here salt removal will be realized by exploiting the ion-ion interactions between salts and CO2-responsive diamines. The thesis describes the salt removal process based on 1) the synthesis of insoluble diamines, 2) the development of an experimental set-up for seawater desalination, 3) the commercial viability of the desalination technology, and 4) the energy consumption of the process.

Chapter 1 discusses the CO2-induced bicarbonate-carbonate buffer system in water. It describes the change in the thermodynamic equilibrium between CO2 and water by the addition of base. Base-CO2 adducts in solution result in different CO2-responsive aqueous systems. The structureproperty relationship of CO2-responsive small molecules amines and their polymeric variants contributes to the understanding of their application in post-combustion carbon capture, oil-water separation, and desalination.

Chapter 2 discusses the desalination studies conducted using alkylated diamines. These studies highlight the drawbacks of using small molecule diamines, hence insoluble polyamines were synthesized and tested for desalination of model and real seawater. The experimental data shows chloride removal via CO2-mediated ion exchange with the polyamines, in the aqueous phase. Further, the chloride removal efficiency, the regeneration capability of polyamines, and their chloride removal capacity after multiple regeneration cycles will be discussed.

Chapter 3 discusses the structural changes within polyamines. The influence of alkylation on polymer insolubility is investigated using differential scanning calorimetry and powder X-ray diffraction. NMR-spectroscopic studies showed changes in the chemical structure due to CO2induced protonation. The chloride removal from the aqueous solution was concluded with the analysis of the desalinated solution (filtrate), while the impact of CO2 responsiveness and the presence of chloride within the polymer was examined via thermogravimetric analysis. The thermal profile revealed the presence of protonated and deprotonated regions within polyamines.

Chapter 4 describes the development of a continuous flow system for the proposed desalination technology to test the commercial viability of the process. Alkylation of polyamines, although induced insolubility, exhibited slower CO2 responsive behavior and poor water permeability resulting in longer desalination run-time. The continuous flow system was therefore packed with diamine functionalized porous polymer. This operational and material optimization resulted in a 5-fold reduction in desalination run-time with better chloride removal efficiency. Further discussion on energy consumption using the optimized desalination setup will be demonstrated.