Separation of SF6 from Gas Mixtures Using Gas Hydrate Formation

Abstract

This study aims to examine the thermodynamic feasibility of separating sulfur hexafluoride (SF6), which is widely used in various industrial fields and is one of the most potent greenhouse gases, from gas mixtures using gas hydrate formation. The key process variables of hydrate phase equilibria, pressure-composition diagram, formation kinetics, and structure identification of the mixed gas hydrates, were closely investigated to verify the overall concept of this hydrate-based SF6 separation process. The three-phase equilibria of hydrate (H), liquid water (LW), and vapor (V) for the binary SF6 + water mixture and for the ternary N2 + SF6 + water mixtures with various SF6 vapor compositions (10, 30, 50, and 70%) were experimentally measured to determine the stability regions and formation conditions of pure and mixed hydrates. The pressure-composition diagram at two different temperatures of 276.15 and 281.15 K was obtained to investigate the actual SF6 separation efficiency. The vapor phase composition change was monitored during gas hydrate formation to confirm the formation pattern and time needed to reach a state of equilibrium. Furthermore the structure of the mixed N2 + SF6 hydrate was confirmed to be structure II via Raman spectroscopy. Through close examination of the overall experimental results, it was clearly verified that highly concentrated SF6 can be separated from gas mixtures at mild temperatures and low pressure conditions.