Clathrate formation in the Bu4NCl NH4Cl H2O system

Thermal and Crystallographic Properties of Tetra-n-butylammonium Bromide + Tetra-n-butylammonium Chloride Mixed Semiclathrate Hydrates

“…Figure and Table present the phase equilibrium conditions of the hydrate samples for each composition, and show the dependence of equilibrium temperature on (a) x guest and (b) x TBAB . The equilibrium temperatures of the pure TBAB and TBAC hydrates are consistent with the data from previous studies. ,− Comparing these data to those reported by Shi et al reveals that there are differences between the values for similar compositions; however, the overall trends for the dependence of equilibrium temperatures on x guest are similar. It is possible that the mismatching data are due to differences in the measurement procedures and/or methods employed in the two studies.…”

“…The hydration numbers of TBAB and TBAC hydrates increase with decreasing x guest , and the hydration number of tetragonal TBA salt hydrates without crystal distortion is n = 32. However, hydrate crystals exhibiting significant distortion (i.e., lower hydration numbers) form as the most stable system at higher concentrations. ,,,,,, It has been reported that the structural transition point between the tetragonal TBAB hydrate with n = 26 and the orthorhombic hydrate with n = 38 is located around x guest = 0.014, − thus the results shown in Figures a and a agree well with the previous studies. − Furthermore, a computational study by Fukumoto et al predicted that TBAC hydrates with n = 32 would be formed as the most stable crystal below x guest = 0.0124. This indicates that the tetragonal TBAC hydrates without crystal distortion are formed by the saturation of the hydration number below x guest = 0.012.…”

“…Latent heat storage systems using semiclathrate hydrates as phase-change materials (PCMs) are efficient systems for thermal and cold energy storage, as has been reported by several research groups. − Liquid–solid (hydrate) transitions of TBA and TBP salt hydrates occur at relatively high latent heats in (273–301) K. The maximum equilibrium temperatures are (300.6–300.8) K for TBA fluoride (TBAF) hydrates, − (288.2–288.3) K for TBA chloride (TBAC) hydrates, − (285.2–285.9) K for TBA bromide (TBAB) hydrates, − and (281.5–282.4) K for TBP bromide (TBPB) hydrates. − The dissociation enthalpies of those hydrates are ca. 240 J·g –1 at hydration number n = 32 and ca.…”

“…The equilibrium temperatures of TBA and TBP salt hydrates vary with the concentration of the aqueous solutions in which they are prepared. − ,− ,, The dissociation enthalpies of TBA salt hydrates increase with increasing hydration number, ,,,,, and this hydration number increases with decreasing concentration of the solution in which the hydrate crystals are formed. ,,− ,− ,,, TBAB hydrates form tetragonal or orthorhombic crystal systems with different hydration numbers. Tetragonal TBAB hydrates with n = (24 or 26) form predominantly when x guest is above ca.…”

“…The equilibrium temperatures of TBA and TBP salt hydrates vary with the concentration of the aqueous solutions in which they are prepared. [9][10][11][12][14][15][16][17][18][19]31,32 The dissociation enthalpies of TBA salt hydrates increase with increasing hydration number, 7,10,14,16,32,33 and this hydration number increases with decreasing concentration of the solution in which the hydrate crystals are formed. 5,6,[8][9][10][12][13][14]16,31,32 below ca.…”