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

Abstract

This paper reports the experimentally determined thermodynamic stability conditions for the hydrogen semiclathrate hydrate generated from tetrabutyl ammonium nitrate (TBANO3) aqueous solutions at two mole fractions, 0.037 and 0.030, corresponding to the stoichiometric composition for TBANO3·26H2O and TBANO3·32H2O, respectively. The experiments for this three-component TBANO3 + 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 TBANO3·26H2O + H2 is more stable than that of TBANO3·32H2O + H2, 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 32) MPa. It was found that the mean dissociation enthalpies for the hydrogen–TBANO3·26H2O and hydrogen–TBANO3·32H2O clathrate hydrate systems were 322.53 kJ·mol–1 and 340.23 kJ·mol–1, respectively.