Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 140

Phase Relations and Binary Clathrate Hydrate Formation in the System H2-THF-H2O

Anderson, R., Chapoy, A., and Tohidi, B.

Langmuir, 23, 3440-3444 (2007)

Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a function of aqueous tetrahydrofuran (THF) concentration from 260 to 290 K at pressures up to 45 MPa. Data are consistent with the formation of cubic structure-II (CS-II) binary H2−THF clathrate hydrates with a stoichiometric THF to water ratio of 1:17, which can incorporate modest volumes of molecular hydrogen at elevated pressures. Direct compositional analyses of the clathrate phase, at both low (0.20 mole%) and stoichiometric (5.56 mole%) initial THF aqueous concentrations, are consistent with observed phase behaviour, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80 to 90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures >30 MPa, giving a clathrate formula of (H2)≤2.THF.17H2O. Results should help to resolve the current controversy over binary H2-THF hydrate hydrogen contents; data confirm recent reports which suggest a maximum of ~1 mass% H2 − this contradicting values of up to 4 mass% previously claimed for comparable conditions.

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