Thermophysical Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylphosphonium Malonate

Ionic semiclathrate hydrate is a crystalline compound mainly composed of water, which can dissociate at ordinary pressure and temperature. Ionic semiclathrate hydrates have been widely studied to develop prospective green and safety phase change materials utilized in a thermal energy storage system to cool batteries, in air conditioning, and in a cold chain system. The thermophysical properties, such as equilibrium temperature and dissociation heat, and the mass fraction dependence of such properties need to be carefully investigated to design such systems. In this study, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium malonate ionic semiclathrate hydrates were experimentally determined at various mass fractions through an established method: the maximum value of the dissociation heat was 179.70 kJ·kg⁻¹ at w = 0.357 and the equilibrium temperature was 8.9 °C at w = 0.357. By comparing tetrabutylphosphonium malonate ionic semiclathrate hydrates with other media in terms of the measured equilibrium temperature and the dissociation heat, the usability of the hydrates as thermal energy storage media for general air conditioning was discussed.