Phase equilibrium temperature and dissociation heat of ionic semiclathrate hydrate formed with tetrabutylammonium butyrate

Thermophysical Property Measurements of Tetrabutylphosphonium Oxalate (TBPOx) Ionic Semiclathrate Hydrate as a Media for the Thermal Energy Storage System

“…In the previous studies of ionic semiclathrate hydrates, similar tendencies of temperature increase and decrease with mass fraction in solution were reported (Yamauchi et al, 2017a , b ; Arai et al, 2018 , 2019 ; Shimada et al, 2018 , 2019 ). From the low mass fraction to a specific mass fraction for each ionic semiclathrate hydrate, the phase equilibrium temperature tended to rise with the increase of the mass fraction.…”

“…After keeping at −20 • C for 10 min to complete the formation of the hydrate crystals, the system temperature was increased from −20 • C to 20 • C under a heating rate of 2 • C min −1 to dissociate the hydrate crystals. The reliability of the higher heating rate of 2 • C min −1 used in this process in determining the dissociation temperature was shown in previous studies (Yamauchi et al, 2017a;Arai et al, 2018;Shimada et al, 2018).…”

“…Three different samples prepared from three different TBPOx aqueous solutions were measured for a given mass fraction. The visual observations with the similar apparatus and method were performed in the previous studies (Yamauchi et al, 2017a , b ; Arai et al, 2018 , 2019 ; Shimada et al, 2018 ; Koyama et al, 2019 ). These studies supported the reliability of the equilibrium temperature obtained in this study.…”

“…Clathrate hydrates are crystalline compounds consisting of the space-filling cages of water molecules and other molecules called guest compounds enclosed within the cages. They show various physical properties depending on the type of guest compounds contained (Nakayama and Hashimoto, 1980 ; Nakayama et al, 1983 ; Mayoufi et al, 2011 ; Sakamoto et al, 2011 ; Sato et al, 2013 ; Yamauchi et al, 2017a , b ; Arai et al, 2018 ; Shimada et al, 2018 , 2019 ). Ionic semiclathrate hydrates have unique structures.…”

“…The semiclathrate hydrates composed with anions with carboxylic acid anions in the guest compounds have been previously investigated (Nakayama and Torigata, 1984 ; Yamauchi et al, 2017a , b ; Arai et al, 2018 ; Shimada et al, 2018 , 2019 ). Carboxylic acid anion containing compounds are more environmentally benign, unlike those which incorporate halide anions.…”