Phase Equilibria of Semiclathrate Hydrate for Nitrogen in the Presence of Tetra-n-butylammonium Bromide and Fluoride

Semiclathrate hydrate phase equilibria for N2 + TBAB (tetra-n-butylammonium bromide) + water mixtures were measured in the temperature range of (280 to 290) K and in the pressure range of (4.0 to 9.2) MPa at TBAB, w (weight fraction) = 0.05, 0.20, 0.40, and 0.60. Also, semiclathrate hydrate phase equilibria for N2 + TBAF (tetra-n-butylammonium fluoride) + water mixtures were measured in the temperature range of (293 to 302) K and in the pressure range of (2.0 to 9.7) MPa at TBAF, w = 0.10, 0.20, 0.34, and 0.45. The equilibrium dissociation temperatures for each pure TBAB and TBAF semiclathrate were also measured at the same concentrations under atmospheric conditions. The presence of TBAB or TBAF remarkably shifted the equilibrium conditions of the double semiclathrates to higher temperature and lower pressure regions when compared with those of the pure N2 hydrate. The highest stabilization effect was observed at the stoichiometric concentrations of each semiclathrate (TBAB, w = 0.40; TBAF, w = 0.34).