Search

Phase equilibrium conditions for tetrabutylphosphonium chloride (TBPC) + CH4 double semiclathrate hydrates (SCHs) were determined to evaluate the stabilization effect of TBPC for potential applications of hydrate-based gas separation and storage. The equilibrium data revealed that TBPC strongly enhances the stability of CH4 hydrates by increasing the equilibrium temperature at a given pressure, and the system showed the strongest stabilization effect at a TBPC mass fraction of 0.30. The dissociation enthalpies of (TBPC + CH4) SCHs were calculated from the experimental data obtained in this work using the Clausius-Clapeyron equation and the Peng-Robinson equation of state. It was found that the mean dissociation enthalpies for (TBPC + CH4) SCHs with TBPC mass fractions of 0.05 to 0.50 were (135.49 to 158.32) kJ·(mol of CH4)-1, which were much higher than that of the pure CH4 hydrate. In addition, to identify the molecular behavior and hydrate structure, Raman spectroscopy measurements were conducted at 203 K. The spectra demonstrated that (TBPC+ CH4) SCHs were formed in tetragonal structure I with small 512 cages trapping CH4 molecules. [ABSTRACT FROM AUTHOR] more...

Dissociation temperatures of mixed tetrabutylammonium bromide (TBAB) + tetrabutylammonium chloride (TBAC) semiclathrate hydrates were determined by using the DSC technique. The system was measured in five groups with a fixed total mole fraction (x = 0.0100, 0.0200, and 0.0337), TBAB mole fraction (xTBAB = 0.0370) or TBAC mole fraction (xTBAC = 0.0337). The obtained results demonstrated that at a given x, the dissociation temperatures of mixed (TBAB + TBAC) semiclathrate hydrates were all higher than that of pure TBAB hydrate, and the maximum dissociation temperature appeared at xTBAB/x = 0.25 instead of xTBAB/x = 0 or 1 (corresponding to pure TBAC or TBAB hydrate). In addition, for systems with fixed xTBAB or xTBAC, TBAC gained the control of forming TBAC semiclathrate hydrate preferentially. [ABSTRACT FROM AUTHOR] more...

Dissociation data for the semiclathratehydrates formed with tetraamylammoniumbromide (TAAB: C20H44NBr) + CH4,+ CO2, or + N2were measured in the pressurerange of (1.33 to 20.37) MPa and temperature range of (279.8 to 291.9)K at (0.050 and 0.100) mass fraction of TAAB. The experimental datawere obtained by employing an isochoric pressure-search method. Theresults showed that at a given pressure, the temperature requiredto form double TAAB + CH4, + CO2, or + N2hydrates was higher than that required for the correspondingpure CH4, CO2, or N2hydrates, andas the TAAB concentration increased, its effect of enlarging the hydratestability zone was strengthened. However, the experimental dissociationtemperatures for double semiclathrate hydrates were lower than thosefor TAAB hydrates formed without guest gases. In addition, the datafor double semiclathrate hydrates formed from TAAB generated in thiswork were compared with those formed from some other semiclathratehydrate formers (such as tetrabutylammonium bromide, tetrabutylammoniumchloride, and tetrabutylammonium fluoride) reported in literature. [ABSTRACT FROM AUTHOR] more...