Effect of organic matters on three phase equilibrium of carbon dioxide hydrate in clay mineral suspensions

Abstract

In this research, phase equilibrium of gas hydrates under diverse marine sediment conditions were in-vestigated to provide a fundamental knowledge to deliver new insights for the successful CO2 sequestration in the near future. In the first chapter, effect of organic matters on CH4 and CO2 hydrate phase equilibrium and the CH4-CO2 replacement kinetics were experimentally investigated. Representative sediment organic matters (glycine, glucose, urea) were selected and it was shown that the addition of organic matters affects CH4 and CO2 hydrate equilibrium conditions that the higher pressure and lower temperature are needed to be stabilized as gas hydrates. Association of organic matters with water molecules led to the decrease of water activity which made the water molecules hard to nucleate and form the crystalline structure to be hydrates. Solvation free energies of each organic matters were measured using computational calculation and compared with the experimental results. Based on the phase equilibrium conditions of CH4-CO2 hydrate, replacement kinetics were measured at different temperature and pressure conditions. The data showed that the replacement ki-netic of CH4-CO2 hydrate decreased in the presence of organic matters compared to Deionized water (DIW). As calculated solvation free energy indicated, organic matters with higher solvation free energy leaded to the slower replacement kinetics. In the second chapter, the effect of phyllosilicate clays on CO2 hydrate phase equilibrium condition with and without organic matter were investigated. Three phyllosilicate minerals (Na-montmorillonite (Na-MMT), kaolinite, illite) were selected as representative clay minerals in marine sedi-ments. Non-expansible clays such as kaolinite and illite did not affect the phase equilibrium of CO2 hydrate while an expansible clay, Na-MMT inhibited the CO2 hydrate phase equilibrium conditions because of the high amount of interlayer cation in the inner space of Na-MMT. By a...