Setting the foundations for a highly selective fractional crystallization scheme to capture carbon dioxide from coal-fired boiler emissions

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In this application, I am proposing to lay the theoretical and experimental foundations that will eventually lead to a less costly technique to remove CO2 from either the pre- or post-combustion gas stream of a coal-fired power plant. Semi-clathrates are a crystalline material that form when gases such as CO2 are contacted with an aqueous solution of a salt such as Tetra-n-butyl ammonium bromide (TBAB) under the appropriate set of temperature and pressure conditions. Semi-clathrates have many similarities to gas-hydrates. Like gas hydrates, semi-clathrates provide a molecular cage of water molecules that are capable of selectively trapping molecules such as CO2. However, semi-clathrates formed in aqueous solutions of TBAB form at substantially lower pressures, at a given temperature, than gas-hydrates. In spite of the recent gains which have been made in understanding semi-clathraes, there are still two fundamental pieces missing before one can begin to design an industrial scale process to remove CO2 via fractional crystallization with TBAB semi-clathrates. The first missing piece is a thermodynamic model to compute the chemical potential of water in the solid semi-clathrate phase. Since TBAB molecules directly incorporate themselves into the network of water molecules in a semi-clathrate, the thermodynamic model that describes gas hydrates is not valid. Secondly, there are no experimental data available on the kinetics of semi-clathrate formation and this is required for the detailed design of process equipment in which semi-clathrates would be formed. Thus, the scope of this proposal is twofold; to develop and test a thermodynamic model for computing the thermodynamic properties of semi-clathrates and secondly, to obtain experimental data on the kinetics of semi-clathrate formation and decomposition. It should be noted that these studies have not been undertaken in any form and their successful completion will be a contribution that puts Canada at the forefront of semi-clathrate research.