Some New Halogen-containing Hydrate-formers for Structure I and II Clathrate Hydrates1

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Abstract
The clathrate hydrate-forming capabilities of 15 hydrofluorocarbon (HFC), fluorocarbon (FC), hydrochlorofluorocarbon (HCFC) and chlorofluorocarbon (CFC) guests are reported. These molecules form stable clathrate hydrates at T > 0°C and have been characterized in detail by X-ray powder diffraction and the measurement of the decomposition temperature, T decomp. The clathrate hydrate structure type depends on the size of the guest molecule and is consistent with the known trend: guest r VDW = 4.1–5.9 Å gives structure I, guest d VDW < 4.1 Å or = 5.6–6.9 Å gives structure II. In addition, the phase diagram of the 1,1-dichloro-1-fluoroethane (R-141b) clathrate hydrate system is reported with a quadruple point of T = 8.4°C and P = 415 mbar. A number of guests give hydrates with relatively high decomposition temperatures (T ∼ 10°C) at low vapour pressures (P < 1 bar) that may be suitable for industrial applications.

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