Guest distributions and dissociation enthalpy of fluorinated gas (CHF3 or C2F6)+N-2 hydrates for hydrate-based gas separation

Abstract

Fluorinated gases (F-gases), such as CHF3 and C2F6, which are used in the semiconductor industry and have considerable global warming potential, can be recovered after use through a gas hydrate-based separation method to prevent their release into the atmosphere. In this study, the guest distributions and dissociation enthalpy (Delta H-d) of F-gas (CHF3 or C2F6)+N-2 hydrates with different F-gas concentrations (CHF3: 20%, 80%, and 100% and C2F6: 20%, 60%, 80%, and 100%) were experimentally investigated using a powder X-ray diffractometer and a high-pressure micro-differential scanning calorimeter, respectively. At high N-2 concentrations in the feed gas, the occupancy of N-2 in the small (5(12)) cages of the F-gas+N-2 hydrates increased significantly. As a result, the F-gas+N-2 hydrates exhibited reduced hydration numbers at high N-2 concentration. The Delta H-d values (in kJ/mol gas) of the F-gas (CHF3 or C2F6)+N-2 hydrates decreased with increased N-2 concentration. The overall experimental results provide useful insights into the design and operation of gas hydrate-based F-gas separation processes.