Abstract
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 mol %) and stoichiometric (5.56 mol %) initial THF aqueous concentrations, are consistent with observed phase behavior, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80-90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures of >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 that suggest a maximum of ~1 mass % H2, this contradicting values of up to 4 mass % previously claimed for comparable conditions.
Original language | English |
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Pages (from-to) | 3440-3444 |
Number of pages | 5 |
Journal | Langmuir |
Volume | 23 |
Issue number | 6 |
DOIs | |
Publication status | Published - 1 Mar 2007 |