Computational and Spectroscopic Studies of Dichlorofluoroethane Hydrate Structure and Stability

Abstract

Clathrate hydrates consisting of HCFC (hydrochlorofluorocarbon) guest molecules within host water cages represent a promising new medium for water desalination. The HCFC used in this study, 1,1-dichloro-1-fluoroethane (R141b), forms a structure II hydrate phase at mild conditions (0 °C, 0 atm). We present a detailed molecular picture of the structure and dynamics of guest R141b molecules within water cages, obtained from ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Such information will be needed to understand and control the nucleation and growth of these hydrates for industrial applications. Density functional theory calculations were used to provide an energetic and molecular orbital description of R141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer, 1,2-dichloro-1-fluoroethane, does not form at ambient conditions due to extensive overlap of electron density between guest and host. Results for the isomer hydr...