Calorimetric and PXRD studies of ionic clathrate hydrates of tetrabutylammonium carboxylates in binary (C4H9)4NCnH2n+1CO2–H2O (n = 0–3) systems

Abstract

The crystal structure of the ionic clathrate hydrates of peralkylonium salts consists of hydrogen-bonded water molecules and anions forming host cage-like water-anion lattice, while peralkylonium cations are included into the cages of the lattice as guests. The ionic clathrate hydrates of some peralkylonium salts are considered as potentially applicable in various fields including gas separation, gas storage and transportation, cold storage and transportation. In this work, we report a synthesis and experimental measurements of compositions, melting points, enthalpies of fusion, as well as the results of the PXRD studies of eight ionic clathrate hydrates of tetrabutylammonium carboxylates formed in (C4H9)4NCnH2n+1CO2–H2O (n = 0–3) binary systems. The enthalpies of fusion values of these hydrates are measured for the first time. Three structural types were observed in the studied systems: on the base of tetragonal structure-I, cubic structure-I, and hexagonal structure-I. The data on thermal properties of studied ionic clathrate hydrates indicate that they are promising as phase change materials for cold storage and air-conditioning systems.