Methane semi-clathrate hydrate phase equilibria with tetraisopentylammonium fluoride

Thomas J. Hughes, Kenneth N. Marsh

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Semiclathrate hydrates (SCH), containing organic salts, typically tetraalkylammonium based, have vacant cages that can be occupied by gas molecules, and some exhibit melting temperatures at atmospheric pressure of greater than 300 K. The aim of this work was to investigate the p, T phase equilibria of the SCH former tetraisopentylammonium fluoride, specifically at a composition of (i-C 5H 11) 4NF·38H 2O, in the presence of methane. Dissociation temperatures were measured at pressures from (0.57 to 26.7) MPa. At 26.7 MPa the dissociation temperature of the SCH increased to about 320 K about 15 K higher than the melting point observed by McMullan and Jeffrey (J. Chem. Phys. 1959, 31, 1231-1234) at atmospheric pressure. We also observed that at atmospheric pressure the SCH can enclathrate methane up to its melting point, this being over 110 K higher than the equilibrium dissociation temperature of methane hydrate at the same pressure. At 10 MPa the SCH dissociation temperature was about 29 K higher than the methane hydrate dissociation temperature. The transport of natural gas over maritime distances greater than 1000 km is most often achieved by cryogenic liquefaction to produce liquefied natural gas (LNG) for tanker shipment. Natural gas hydrates have been suggested as an alternative storage method to LNG tanker transportation by Berner (The Marine Transport of Natural Gas In Hydrate Form. Proceedings of the Second International Offshore and Polar Engineering Conference, San Francisco, CA, June 14-19, 1992; pp 636-643) and Gudmundsson and Børrehaug (Petrol. Rev. 1996, 50, 232-235). At atmospheric pressure natural gas hydrates are stable only at low temperature, less than 240 K. Semiclathrate hydrates are a possible methane storage alternative to natural gas hydrates.

Original languageEnglish
Pages (from-to)4597-4603
Number of pages7
JournalJournal of Chemical and Engineering Data
Issue number12
Publication statusPublished - 8 Dec 2011
Externally publishedYes

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