Phase Equilibria and Thermodynamic Properties of Some Branched Alkyl Ethers

Abstract

The low-temperature heat capacity and thermodynamic properties of the solid-to-solid transition and fusion of di-isobutyl ether (DIBE) were determined by adiabatic calorimetry in the temperature range from (8 to 373) K. The saturation vapor pressure of DIBE was determined by a comparative ebulliometry over the moderate pressure range from (10.8 to 99.6) kPa. A density of liquid DIBE was measured in the temperature interval from (298 to 313) K using a quartz pycnometer. The normal boiling temperature, Tn.b., the enthalpy of vaporization at T = 298.15 K and Tn.b., and the ideal gas thermodynamic functions (changes of the entropy, enthalpy, and Gibbs energy) at T = 298.15 K were derived. Appropriate thermodynamic functions over a wide temperature range from (150 to 1000) K and the standard enthalpy of formation at T = 298.15 K were computed by the methods of statistical thermodynamics (ST) and the density functional theory (DFT) on the level B3LYP/6-31G(d,p). The experimental data on the vapor pressure of DIBE were extended to the entire range of liquid phase from the triple to the critical temperatures by the corresponding states law and combined treatment of the pT-parameters and the low-temperature differences between the heat capacities of the ideal gas and liquid. The data on thermodynamic properties of some branched ethers, C5 to C9, studied earlier and in this work were critically analyzed for verification of their reliability and mutual consistency.