Phase equilibria and characterization of CO 2 and SF 6 binary hydrates for CO 2 sequestration

Both CO 2 and SF 6 are potent greenhouse gases responsible for global warming and associated environmental issues. Hydrate-based separation and capture of these gases from gas mixtures produced by industry have been proposed, and improving the commercial viability of these processes is crucial. Here, we report the phase equilibria and characterization of binary hydrates containing CO 2 and SF 6 . The introduction of SF 6 considerably lowered the formation pressure of CO 2 hydrates by readily occupying the structure II hydrate cages and hence altering the crystal structure. Hydrate phases with different crystalline structures were found to coexist as a result of competition in occupying different hydrate cages. The structural instability caused by the coexistence of structure I and II hydrates was observed, and this feature would be important to understand the mixed gas hydrate systems. The ability of SF 6 to significantly reduce the formation pressure of hydrates suggests that it has a potential to serve as a hydrate promoter. This feature of SF 6 combined with its non-toxic and non-flammable properties would be efficient for practical applications such as CO 2 sequestration using hydrates.