Benchmark properties of biphenyl as a liquid organic hydrogen carrier: Evaluation of thermochemical data with complementary experimental and computational methods

Vapor pressures of highly pure biphenyl were measured by the transpiration method over a broad temperature range that included both the crystalline and the liquid phases. The standard molar enthalpies of sublimation/vaporization of biphenyl were derived from the vapor pressure temperature dependences. Thermodynamic data on sublimation/vaporization processes available in the literature were collected, evaluated, and combined with our experimental results. Additional combustion experiment on the highly pure biphenyl helped to resolve an ambiguity on the crystalline phase enthalpy of formation of biphenyl. We recommend the set of sublimation/vaporization and formation enthalpies for biphenyl at 298.15 K (in kJ·mol−1): ΔcrgHmo=(81.8±0.2), ΔlgHmo=(65.8±0.2), ΔfHmo(cr)=(97.9±1.1), and ΔfHmo(g)=(179.7±1.1), as the reliable benchmark properties for further thermochemical calculations. Gas phase molar enthalpies of formation of biphenyl, calculated by high-level quantum-chemical method G3MP2, were found in excellent agreement with the recommended experimental data. The standard molar entropy of formation and the standard molar Gibbs function of formation of biphenyl were estimated. The hydrogenation/dehydrogenation reaction enthalpy was calculated and compared with the data for other liquid organic hydrogen carriers.