Preparation and Characterisation of Ionic Liquids and Investigations into their Potential use in the Absorption and Sequestration of Carbon Dioxide

The first area of the research presented in this thesis pertains to the synthesis and characterisation of novel ionic liquids. Three distinct categories of ionic liquids were synthesised, two of which are imidazolium based, with the latter category based on the phosphonium cations. The first category consist of cations which contain two N-heterocyclic rings and these are combined with a range of conventional anions such as bis(triflimide) and dicyanamide. The second category utilise the same cations but have amino acids as the anion in their carboxylate form, introducing NH2 functionality into the ionic liquids and as such can be used in CO2 absorption investigations. The last category of ionic liquids, are those which contain a phosphonium cation (trioctyl) quaternised with a number of groups containing different functionalities for different potential applications. In particular a pyrrole functionalised quaternary phosphonium salt was successfully polymerised. The novel ionic liquids were employed in two main areas of investigation. Imidazolium ionic liquids containing conventional anions were immobilised onto a polymeric support, after which gases which are found in flue gas systems such as CO2 and N2, are passed through the membrane. The gases pass through at different rates due to the differing affinity of the liquids for the individual gases and as such separation of the gases is possible. These preliminary comparative permeability studies were confined to the first category of ionic liquids due to their lower viscosity and previous literature precedent of these anion types being used for these systems. Both single and binary ionic liquid systems were examined throughout the course of the investigation with the binary systems exhibiting some benefits in CO2/N2 selectivity. Amino acid ionic liquids were immobilised onto a mesoporous silica (MCM-41) and their CO2 absorption capability was investigated. These contained NH2 functionality and as such are capable of CO2 absorption through the formation of a carbamate species. The low volatility of the ionic liquids compared to amines, such as monoethanolamine (MEA), which are currently used in CO2 gas capture technologies, make them an attractive area of research. A preliminary operational evaluation was conducted to examine anionic and cationic effects, as well as temperature and ionic liquid content of the impregnated MCM-41 silica