Phase equilibria, dissociation enthalpies, and Raman spectroscopic analyses of N2 + tetra-n-butyl ammonium chloride (TBAC) semiclathrates

Abstract

The thermodynamic phase behaviors, dissociation enthalpies, and Raman spectra of N2 + tetra-n-butyl ammonium chloride (TBAC) + water systems were measured in order to investigate the enclathration of N2 in TBAC semiclathrates. The three-phase (H-Lw-V) equilibria of the N2 + TBAC (1.0, 3.3, and 5.0 mol%) semiclathrates measured using a high pressure vessel as well as a high pressure micro-differential scanning calorimeter (HP μ-DSC) indicated that the N2 + TBAC semiclathrates have significant stability in the thermodynamic equilibrium compared with the N2 gas hydrate and that they also exhibit maximum thermodynamic stability at 3.3 mol%, which corresponds to the stoichiometric concentration of TBAC·29.7H2O. The dissociation enthalpies of the N2 + TBAC semiclathrates were determined from the endothermic dissociation thermograms of a HP μ-DSC under pressure. The Raman spectroscopic results clearly demonstrated that N2 molecules are enclathrated in the cages of the TBAC semiclathrate. From the overall experimental results, TBAC is expected to be an effective semiclathrate former that can reduce the equilibrium dissociation pressure or enhance the equilibrium dissociation temperature for enclosing N2 molecules as a guest in the vacant cages of TBAC semiclathrates.