Hydrogen Storage in Semiclathrate Hydrates of Tetrabutyl Ammonium Chloride and Tetrabutyl Phosphonium Bromide

Original calorimetric and phase equilibrium properties for hydrogen + tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBACl), or tetrabutylphosphonium bromide (TBPB) semiclathrate hydrates were measured using differential scanning calorimetry under pressure. The dissociation temperatures of H(2) + TBACl and H(2) + TBPB semiclathrate hydrates are very close to the ambient temperature at low pressures around 15.0 MPa. H(2) + TBACl and H(2) + TBPB systems therefore exhibit better and comparable stability than the H(2) + TBAB system at equivalent pressure, respectively. The amount of hydrogen stored in H(2) + TBACl and H(2) + TBPB semiclathrate hydrates was estimated in terms of the H(2)-to-water mole ratio (n(H2)/n(H2O)) calculated from disssociation enthalpies and (p, T) equilibrium data. In terms of mass fraction deduced from the ratio (n(H2)/n(H2O)), H(2) + TBACl and H(2) + TBPB semiclathrate hydrates can store 0.12 To and 0.14 To of hydrogen, respectively. Moreover, the quantity of hydrogen stored in these two semiclathrate hydrates is significantly higher than that stored in the H(2) + TBAB system.