Phase Equilibria and13C NMR Analysis of the Double Semi-Clathrates Containing TBAB

TBAB (tetra-n-butyl ammonium bromide) forms a semi-clathrate with water under atmospheric pressure conditions and recently has attracted great attention due to its usage as a thermodynamic promoter in gas storage and separation process using gas hydrate formation. In this study, we measured the three-phase (hydrate (H) - liquid water ()-vapor (V)) equilibria of the ternary +TBAB+water and +TBAB+water mixtures at the TBAB concentrations of 5 and 32 wt% to investigate promoting characteristics of TBAB. The greater promotion effect of TBAB was observed at 32 wt% than at 5 wt%. This result was in good agreement with that from pure TBAB semi-clathrate phase diagram under atmospheric pressure conditions. Through NMR analysis of the +TBAB semi-clathrate, it was found that molecules are enclathrated in the cages of the double semi-clathrate and the position of resonance peak from encaged molocules in the double semi-clathrate is the same as that from encaged molocules in the pure hydrate of structure I.