The need to create a new approach to carbon capture processes that are economically viable has led to the design and synthesis of sorbents that selectively capture carbon dioxide by physisorption. Solid Ionic Liquids (SoILs) were targeted because of their tunable properties and solid form under operational conditions. Molecular modelling was used to identify candidate SoILs and a number of materials based on the low cost, environmentally friendly acetate anion were selected. The materials showed excellent selectivity for carbon dioxide over nitrogen and oxygen and moderate sorption capacity. However, the rate of capture was extremely fast, in the order of a few seconds for a complete adsorb–desorb cycle, under pressure swing conditions from 1 to 10 bar. This showed the importance of rate of sorption cycling over capacity and demonstrates that smaller inventories of sorbents and smaller process equipment are required to capture low concentration CO2 streams. Concentrated CO2 was isolated by releasing the pressure back to atmospheric. The low volatility and thermal stability of SoILs mean that both plant costs and materials costs can be reduced and plant size considerably reduced.