Thermodynamic properties of tetra-n-butylammonium 2-ethylbutyrate semiclathrate hydrate for latent heat storage

The quaternary onium salt-based semiclathrate hydrates have been investigated in many kinds of fields such as latent heat storage materials and gas separation media. In the present study, equilibrium (temperature composition) relations in the tetra-n-butylammonium 2-ethylbutyrate (TBA-2 EB) semiclathrate hydrate system have been measured. In addition, thermodynamic and spectroscopic properties of TBA-2 EB semiclathrate hydrate were analyzed. The maximal equilibrium temperature and stoichiometric concentration of TBA-2 EB semiclathrate hydrate was 283.22 +/- 0.05 K and x(1) = 0.0281 +/- 0.0007, respectively. The crystal lattice of TBA-2 EB semiclathrate hydrate, determined by the single crystal X-ray diffraction, was tetragonal. Other properties, not only Raman spectrum but also the maximum allowable degree of supercooling, in the TBA-2 EB semiclathrate hydrate system were similar to those in the tetra-n-butylammonium bromide (TBAB) hydrate. The TBA-2EB semiclathrate hydrate would be an alternative to TBAB hydrate as a halogen-free semiclathrate hydrate system. (C) 2019 Elsevier Ltd and IIR. All rights reserved.