Phase equilibria and characterization of CO2 and SF6 binary hydrates for CO2 sequestration

Both CO2 and SF6 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 CO2 and SF6. The introduction of SF6 considerably lowered the formation pressure of CO2 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 SF6 to significantly reduce the formation pressure of hydrates suggests that it has a potential to serve as a hydrate promoter. This feature of SF6 combined with its non-toxic and non-flammable properties would be efficient for practical applications such as CO2 sequestration using hydrates. (C) 2017 Elsevier Ltd. All rights reserved.