Phase Equilibria and Dissociation Enthalpies of Hydrogen Semi-Clathrate Hydrate with Tetrabutyl Ammonium Nitrate

This paper reports the experimentally determined thermodynamic Stability, conditions for the hydrogen semiclathrate hydrate generated from tetrabutyl ammonium nitrate (TBANO(3)) aqueous solutions at two mole fractions, 0.037 and 0.030, corresponding to the stoichiometric composition for TBANO(3)center dot 26H(2)O and TBANO(3)center dot 32H(2)O, respectively. The experiments for this three-component TBANO(3) + water + hydrogen system were performed in the temperature range of (281.9 to 284.9) K and pressure range of (9.09 to 31.98) MPa with using a "full view" sapphire cell. An isochoric equilibrium step-heating pressure search method was employed to determine the phase boundary between hydrate liquid vapor (H-L-V) phases and liquid vapor (L-V) phases. The results showed that the semiclathrate hydrate of TBANO(3)center dot 26H(2)O + H-2 is more stable than that of TBANO(3)center dot 32H(2)O + H-2, with both of these semiclathrate hydrates being much more stable than pure hydrogen hydrate. The obtained phase equilibria data were analyzed using the Clausius-Clapeyron equation to determine the dissociation enthalpy at the pressure range from (9 to :3,2) MPa. It was found that the mean dissociation enthalpies for the hydrogen-TBANO(3)center dot 26H(2)O and hydrogen-TBANO(3)center dot 32H(2)O dathrate hydrate systems were 322.53 kJ.mol(-1) and 340.23 kJ.mol(-1), respectively.