Enclathration of CHF 3 and C 2 F 6 molecules in gas hydrates for potential application in fluorinated gas (F-gas) separation

Phase Diagrams and Spectral Characteristics of Hydrofluorocarbon Hydrates: Insights from First-Principles Thermodynamics

“…Takeuchi et al determined the Kihara parameters of difluoromethane and cyclopentane following the phase equilibrium data from hydrate-forming systems containing CH 2 F 2 and cyclopentane, which reproduced the pressure and temperature of the phase equilibrium in a CH 2 F 2 +cyclopentane+H 2 O system. Kim et al measured the phase equilibrium curve of sI CH 3 F hydrate and discovered that it could form under relatively mild conditions. They also reported the three-phase equilibria of a CHF 3 +N 2 +H 2 O system with different concentrations and determined the thermodynamic stability conditions of the CHF 3 +N 2 hydrate .…”

Greenhouse Gas (CHF3) Separation by Gas Hydrate Formation

“…Therefore, the three-phase (H–L W –V) equilibria of the CHF 3 + N 2 + water systems with various CHF 3 concentrations (10%, 20%, 40%, 60%, and 80%) in the temperature range of 275–289 K and pressure range of 0.7–11.5 MPa were measured, and the results are presented in Figure and Table . Also, the H–L W –V equilibrium data of pure CHF 3 hydrate, which were measured in our previous study, and those of pure N 2 hydrate are also presented in Figure to examine the effect of CHF 3 concentrations on the thermodynamic stability of the CHF 3 + N 2 gas hydrates. , As shown in Figure , the H–L W –V equilibrium curves of the CHF 3 + N 2 + water systems were located generally nearer to that of the CHF 3 + water system than that of the N 2 + water system. This is because N 2 forms the sII hydrate at very high pressure conditions, occupying both small (5 12 ) and large (5 12 6 4 ) cages, due to its small molecular size, whereas CHF 3 forms the sI hydrate, primarily occupying large (5 12 6 2 ) cages and partly occupying small (5 12 ) cages. ,− , Therefore, as the CHF 3 concentration in the vapor phase increased, the H–L W –V equilibria of the CHF 3 + N 2 + water systems became thermodynamically more stable as a result of the increased enclathration of a large-sized molecular guest (CHF 3 ).…”

“…The growth process of the CHF 3 + N 2 hydrates formed with deuterium oxide (D 2 O) was monitored using in situ Raman spectroscopy. Because some Raman peaks from CHF 3 molecules overlap with those from H 2 O molecules, D 2 O was used to obtain the precise C–H stretching mode of the CHF 3 molecules enclathrated in the hydrate cages. − The Raman spectra were obtained using a modular Raman spectrometer (SP550, Horiba, France) equipped with a multichannel air cooled CCD detector and a 1800 groove/mm grating. The spectrometer was calibrated with a silicon wafer whose Raman band is at 520.7 cm –1 .…”

“…All the measurements were conducted at least three times, and the average value was taken. More detailed descriptions of the experimental procedure have been provided in our previous studies. − …”

Molecular dynamics simulation of sI methane hydrate under compression and tension

“…When small gas molecules exist, the water molecules bind to each other via hydrogen bond interactions; thereby forming a cage-shaped structure with different shapes and sizes with the gas molecule wrapped in it. Gas and water molecules interact with one another through the van der Waals force, which reduces the energy of the entire structure and achieves a stable state [14,15]. If the polyhedron cage-shaped hydrate lattice formed by the water molecule is not occupied by the guest molecule, then the empty hydrate lattice can be regarded as a special kind of ice, but it is unstable and prone to collapse.…”