Experimental study of the isochoric heat capacity and liquid–gas coexistence-curve properties of sec-butanol in the near- and supercritical regions

One- and two-phase isochoric heat capacities (CV) and saturated liquid and vapor properties (TS,ρ′S,ρ″S)(TS,ρ′S,ρ″S) of sec-butanol in the wide temperature and density ranges including near- and supercritical conditions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 307 K to 551 K for 22 liquid and vapor isochores from 76.44 kg m−3 to 794.06 kg m−3. The isochoric heat capacity jump (quasi-static thermograms) technique have been used to accurately measure of the phase transition parameters (TS, ρS) near the critical point. The total experimental uncertainty of density (ρ), temperature (T), and isochoric heat capacity (CV) measurements at the 95% confidence level with a coverage factor of k = 2 were estimated to be 0.06%, 15 mK, and 2–3%, respectively. The critical temperature (TC = 535.95 ± 0.02 K) and the critical density (ρC = 276.40 ± 2 kg m−3) for sec-butanol were determined from the measured saturated properties (CVS,TS, ρS) near the critical point. The values of the asymptotical critical amplitude of the two-phase CV along the critical isochore A¯0−=37.95) and saturated density (B0 = 1.7441) near the critical point have been calculate using the measured isochoric heat capacity data. The measured two-phase liquid and vapor isochoric heat capacities at saturation and saturation liquid and vapor specific volumes (V′, V″) were used to calculate the values of second temperature derivatives of the vapor pressure and chemical potential near the critical point. The values of asymmetry parameters a3 = −0.3664 and b2 = −0.2527 of the coexistence curve diameter for sec-butanol were determined from the measured heat capacity and saturated density data near the critical point. A new technique of the Yang-Yang anomaly strength parameter (Rμ) determination from the direct simultaneously two-phase isochoric heat capacity (C″V2,C′V2)(C″V2,C′V2) and specific volumes (V″, V′) measurements at saturation have been proposed. The value of Yang-Yang anomaly strength parameter (Rμ = −0.59) for sec-butanol has been determined using the new technique.