Thermodynamic and Structural Investigation of Xe and Kr Hydrates Containing Tetrahydrofuran for Applications in Gas Capture and Storage

Abstract

Noble gases, such as xenon (Xe) and krypton (Kr), can be captured in hydrate cages, and thus, gas hydrates can be used as capture and storage media for these gases. This study examined the phase equilibria, crystal structure, and guest distributions of Xe and Kr hydrates in the presence of tetrahydrofuran (THF). The three-phase [hydrate (H)–liquid (L)–vapor (V)] equilibria of the Xe + THF + water and Kr + THF + water systems were measured at two different concentrations of THF (1.0 and 5.6 mol %) to examine the thermodynamic promotion effect of THF on Xe and Kr hydrates. The inclusion of THF in the hydrate cages led to significant shifts in the equilibrium curves of the Xe and Kr hydrates to lower pressure and higher temperature regions. The powder X-ray diffraction patterns and the 129Xe and 13C nuclear magnetic resonance spectra revealed that THF was enclathrated in the large (51264) cages of structure II hydrates and that the small (512) cages were occupied by Xe (or Kr). In particular, at 1.0 mol % THF, the large 51264 cages were partly occupied by Xe (or Kr) as a result of tuning behavior. The experimental results expand the basic understanding of hydrate-based gas capture and storage for Xe and Kr.

Abnormal structural transformation of tetra-n-butyl ammonium chloride + Xe clathrates and its significance for clathrate-based Xe capture and storage

“…129 Xe NMR is a useful method to examine the structure and guest distributions of gas hydrates enclosing Xe by detecting cage-specific chemical shifts of enclathrated Xe molecules. 6 In this study, 129 Xe NMR spectra were measured to cross-check the formation of cubic sI and to examine the Xe inclusion behavior in the TBAC + Xe + water systems. Fig.…”

“…1,2 Because clathrate hydrates can selectively capture gas molecules such as CH 4 , CO 2 , and Xe and can store a large amount of gas in a unit volume, they can be applied to gas capture and storage applications. [3][4][5][6] The noble gas Xe exists in trace amounts in Earth's atmosphere and is generally unreactive. Because Xe is useful in various industrial applications, the separation and capture of Xe have been pursued for various commercial purposes.…”

“…1,2 Because clathrate hydrates can selectively capture gas molecules such as CH 4 , CO 2 , and Xe and can store a large amount of gas in a unit volume, they can be applied to gas capture and storage applications. 3–6…”

2022 Pioneers in Energy Research: John Ripmeester

“…THF was selected as a thermodynamic hydrate promoter, which exhibits an effective "tuning effect" for better separation of these gases. 47 Quantitative evaluation of clathrate hydrates of different guests coexisting with ice were measured using Xray imaging by comparing their absorption contrast; through this technique, CO 2 hydrates could be differentiated in a mixture with CH 4 hydrates and ice. 48 Generalized phase diagrams were theoretically calculated for the Frank−Kasper clathrate compounds of group 14 elements.…”

“…PXRD and NMR measurements were carried out to study the fractionation of Xe and Kr gas mixture by hydrates. THF was selected as a thermodynamic hydrate promoter, which exhibits an effective “tuning effect” for better separation of these gases . Quantitative evaluation of clathrate hydrates of different guests coexisting with ice were measured using X-ray imaging by comparing their absorption contrast; through this technique, CO 2 hydrates could be differentiated in a mixture with CH 4 hydrates and ice .…”