Thermodynamic Stability of H₂ + Tetrahydrofuran Mixed Gas Hydrate in Nonstoichiometric Aqueous Solutions

Abstract

Phase equilibria (pressure−temperature relations) of the H2 + tetrahydrofuran mixed gas hydrate system have been measured for various concentrations of tetrahydrofuran aqueous solutions. The three-phase equilibrium lines obtained in the present study are shifted to the low-temperature or high-pressure side from that of the stoichiometric THF solution. Each three-phase equilibrium line of H2 + tetrahydrofuran hydrate converges at the three-phase equilibrium line of the pure tetrahydrofuran hydrate. At the cross point on the lines, the tetrahydrofuran concentration of mother aqueous solution agrees with each other. The Raman spectra of H2 and tetrahydrofuran for the H2 + tetrahydrofuran mixed gas hydrate do not change with the variation of tetrahydrofuran mole fraction from 0.010 to 0.130 in the aqueous solution.

Hydrogen Storage Capacity of Tetrahydrofuran and Tetra-N-Butylammonium Bromide Hydrates Under Favorable Thermodynamic Conditions

“…Results from a series of calorimetry experiments suggested that THF forms a binary hydrate with H 2 ; results for TBAB were not definitive. The measured THF+H 2 hydrate stability data agreed well with the results of Hashimoto et al [26] and Anderson et al [27]. To confirm that binary THF + H 2 hydrates had formed in the calorimetry experiments, Raman spectra were taken at different points of the hydrate synthesis process using a separate facility.…”

“…Calorimetry results for binary hydrate formed from aqueous solutions of TBAB are shown in Figures 14 and 15. TBAB has been proposed to reduce the formation pressure of H2 hydrate [6,21,22]. TBAB is known to form semi-clathrate hydrate in which the water cage is broken to accommodate the large TBAB molecule [23].…”

“…In order to reduce the prohibitively high pressure requirement, H 2 mixed gas hydrates have been investigated [1][2][3][4][5]. Hashimoto et al [6] demonstrated that adding small amounts of tetra-n-butylammonium bromide (TBAB; C 16 H 36 NBr) to water reduced the hydrogen hydrate formation pressure from 350 MPa to~1 MPa at 280 K. TBAB is a salt that forms a semi-clathrate hydrate crystal (C 16 H 36 N + ·Br − ·38H 2 O) at atmospheric pressure and near room temperature with a unit-cell composed of 16 small (S)-cages and eight large (L)-cages. The bromide anion forms cage structures with water molecules while the cation occupies empty L-cages [7].…”

Cage Occupancy of Hydrogen in Carbon Dioxide, Ethane, Cyclopropane, and Propane Hydrates

“…(6b). This Raman shift agrees with that of H 2 encaged in the S-cage of s-II hydrate [6,7]. That is, H 2 can selectively occupy the S-cage of s-II hydrate generated from H 2 + propane + water mixture, while propane occupies the L-cage entirely.…”

“…The mixed-gas hydrate systems containing H 2 and suitable additives enable us to perform the H 2 storage at much lower pressure conditions than the pure H 2 hydrate. Tetrahydrofuran (hereafter, THF) is the most familiar of such additives [3][4][5][6][7][8]. In addition, quaternary ammonium salts [6,[9][10][11][12], cyclic hydrocarbons [13] and so on have been reported.…”