Equilibrium temperature and dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate as a medium for the hydrate-based thermal energy storage system

The hydrate-based thermal energy storage system is one of the most effective supplemental technologies to stabilize the energy supply for renewable energies. The system is expected to solve the global energy-management issues related to energy-demand increase and energy supply chain. In fact, this eco-friendly technology requires prospective hydrate candidates for the thermal energy storage media, followed by the extensive investigation of the thermophysical properties of the selected hydrates. In this study, to satisfy these requirements, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate were studied. It was found that the highest equilibrium temperature was 14.4 °C at the mass fractions from 0.37 to 0.40. It was also found that the largest dissociation heat was (210.4 ± 5.3) kJ kg⁻¹ at the mass fraction 0.39. These values indicate that TBPAc hydrate could be a new promising thermal-storage medium for the general or data-centre air-conditioning systems. The experimental results of this study also revealed an underlying tendency between the thermophysical properties of the tetrabutylphosphonium (TBP) + carboxylate salt hydrates and the molar mass of the guest anion in salt.