Thermodynamic phase equilibria of binary SF6–N2O hydrates and their structural analysis for the hydrate-based greenhouse gas capture

The increasing greenhouse gas (GHG) emissions from industrial activities have driven the development of efficient and environmentally safe GHG capture technologies. Clathrate hydrates, primarily composed of water, have attracted significant attention for their potential in GHG capture due to their ability to manage large emissions and their environmental advantages over materials like amine-based sorbents and metal-organic frameworks. This study investigates the hydrate-based capture of SF₆ and N₂O, two potent GHGs, to develop an effective GHG capture process. Phase equilibrium measurements demonstrate that binary SF₆-N₂O hydrates can form under moderate thermodynamic conditions, even with a small proportion of SF₆, highlighting the feasibility of using hydrate-based methods to capture GHG mixtures. Furthermore, the formation of binary SF₆-N₂O hydrates enhances GHG volumetric storage capacity compared to pure SF₆ hydrates. The guest compositions calculated for each binary SF₆-N₂O hydrate phase, along with spectroscopic analyses (Powder X-Ray Diffraction and Raman spectroscopy), confirm that the high GHG uptake in binary hydrates results from N₂O molecules occupying the small cages of structure II hydrates, which are inaccessible to the larger SF₆ molecules. These findings suggest that both the small and large cages of sII hydrates can be practically utilized for efficient capture of GHG mixture (SF₆ and N₂O) under mild conditions, thereby increasing the storage density of GHGs within the hydrate structure.