(156a) CO2 Separation from Fuel Gas by Surfactant-Assisted Gas-Hydrate Process

Separation of methane and CO2 by means of gas hydrates promoted by surfactants is reported. In a surfactant-water-CO2-hydrate system, CO2 enriched the solid hydrate phase during hydrate formation, where thermodynamic system equilibrium ultimately determined CO2 separation extent. Synthetic surfactants and biosurfactants significantly promote gas hydrate formation from nonpolar hydrocarbon gases, but for polar gases, such as CO2, no surfactant to promote CO2 hydrates has previously been reported. In this study, CO2-philic surfactants were developed to selectively promote CO2 hydrate formation and assist separation of a CO2-fuel gas. In the presence of surfactants developed in the study, CO2 was further enriched in the solid hydrate phase compared to hydrate formation from distilled water without surfactant. In the experiments, commercially-available surfactants and laboratory-modified surfactants were screened and tested to selectively promote CO2 hydrates in both quiescent and stirred systems. Separation experiments were conducted on mixtures of 50% CO2 and 50% methane initial gas content. The effects of surfactant concentration, solution pH, pressure, temperature, volume ratio of water to gas, as well as THF additive on the separation are reported. While using laboratory-modified surfactants, gas hydrate formation rates sharply increased when pH values rose to 4.0. The CO2 concentration in the gas phase after hydrate formation with surfactants decreased to as low as 24.53%. From visual observations, surfactants not only increased the formation rate of CO2 hydrate, but also helped accumulate CO2 hydrate on special surfaces and influenced the morphology of the solid hydrates.