Pure SF6 and SF6−N2 Mixture Gas Hydrates Equilibrium and Kinetic Characteristics

Sulfur hexafluoride (SF6), whether pure or mixed with inexpensive inert gas, has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate and/or collect it from waste gas streams. In this study, we investigated the pure SF6 and SF6−N2 mixture gas hydrates formation equilibrium as well as the gas separation efficiency in the hydrate process. The equilibrium pressure of SF6−N2 mixture gas was higher than that of pure SF6 gas. Phase equilibrium data of SF6−N2 mixture gas was similar to SF6 rather than N2. The kinetics of SF6−N2 mixture gas was controlled by the amount of SF6 at the initial gas composition as well as N2 gas incorporation into the S-cage of structure-II hydrate preformed by the SF6 gas. Raman analysis confirmed the N2 gas incorporation into the S-cage of structure-II hydrate. The compositions in the hydrate phase were found to be 71, 79, 80, and 81% of SF6 when the feed gas compositions were 40, 65, 70, and 73% of SF6, respectively. The present study provides basic information for the separation and purification of SF6 from mixed SF6 gas containing inert gases.