Equilibrium Phase Relations and Dissociation Enthalpies of Tri-n-butylalkenylphosphonium Bromide Semiclathrate Hydrates

Abstract

Semiclathrate hydrates (SCHs) have received attention as thermal storage materials because of their equilibrium temperature and relatively large dissociation enthalpy. The alkyl length of quaternary onium cations significantly affects the equilibrium temperature and dissociation enthalpy of quaternary onium salt SCHs. To investigate the effects of the double bond introduced in onium cations, in the present study, the thermodynamic stability of tri-n-butylalkenylphosphonium bromide (P444­(alkenyl)-Br: alkenyl = 3-butenyl (31) or 4-pentenyl (41)) SCH was investigated. The equilibrium temperatures and the dissociation enthalpies were determined to be (277.5 ± 0.1) K and (199 ± 2) J/g for P444(31)-Br SCH, and (274.8 ± 0.1) K and (188 ± 2) J/g for P444(41)-Br SCH. The equilibrium temperatures of P444(31)-Br SCH and P444(41)-Br SCH were lower than those of the corresponding normal alkyl SCHs (P4444-Br and P4445-Br), although the equilibrium temperature of tri-n-butylallylphosphonium bromide SCH was higher than that of the P4443-Br SCH.

Effect of introducing a cyclobutylmethyl group into an onium cation on the thermodynamic properties of ionic clathrate hydrates

“…The D d H app value has a maximum at the stoichiometric composition because the excess amount of water or phosphonium salt remains at a composition except for the stoichiometric composition. 6,19,43 The crystal structure of the P444(1c4)-Br ICH was analysed using powder X-ray diffraction (PXRD). The PXRD patterns were measured at 150 K and atmospheric pressure using a diffractometer (PANalytical, X'Pert-MPD) with a cold stage (Anton Paar, TTK450) and a Cu Ka X-ray (45 kV, 40 mA) source.…”

“…[8][9][10][11][12] ICHs have equilibrium temperatures around 270-300 K, with the dissociation enthalpies around 200 J g À1 . [6][7][8][9][10][13][14][15][16][17][18][19][20][21][22] Their thermodynamic properties, including the equilibrium temperature and dissociation enthalpy, can be adjusted by choosing an appropriate guest species. For example, the tetra-nbutylammonium bromide (TBAB, N4444-Br) ICH has an equilibrium temperature located around 284.8-286.1 K, and a dissociation enthalpy of about 188.8-197.3 J g À1 .…”

“…In addition, several researchers have focused on the differences between the center atoms of the cations, that is, the differences between tetra-n-butylammonium and tetra-nbutylphosphonium cations. 15,16,22,[39][40][41] Recently, we reported the effects of alkyl and alkenyl groups in tri-n-butylalkylphosphonium bromide (P444R-Br) 17 and tri-n-butylalkenylphosphonium bromide (P444(R 1 QR 2 )-Br) 19 on the thermodynamic stabilities of ICHs. The size and shape of the alkyl and alkenyl groups significantly affect the thermodynamic properties of ICHs.…”

Designing the structure and relevant properties of semiclathrate hydrates by partly asymmetric alkylammonium salts

“…36 Recently, the thermodynamic properties of semiclathrate hydrates formed by asymmetric quaternary phosphonium salts whose one side chain was substituted from tetra-nbutylphosphonium (denoted as P 4444 ) by some alkyl and aryl chains, i.e., P 444R , were investigated. 38,39 It was found that the melting temperatures and fusion heats of the quaternary phosphonium salt hydrates were also affected by the side chains.…”

“…, P 444R , were investigated. 38,39 It was found that the melting temperatures and fusion heats of the quaternary phosphonium salt hydrates were also affected by the side chains.…”