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 ) aqueous solutions at two mole fractions, 0.037 and 0.030, corresponding to the stoichiometric composition for TBANO "26H O and TBANO "32H O, respectively. The experiments for this three-component TBANO + 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 ·26H O + H is more stable than that of TBANO ·32H O + H , 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-TBANO ·26H O and hydrogen-TBANO ·32H O clathrate hydrate systems were 322.53 kJ·mol and 340.23 kJ·mol , respectively