Isobaric heat capacity of the binary liquid (water + 1,2–propanediol) mixtures at high-temperatures and high-pressures

Abstract

Isobaric heat capacity, CP, of binary aqueous 1,2 − propanediol solutions have been measured over the temperature range from room temperature 298.15 K to 473.15 K at pressures up to 30 MPa using differential scanning calorimeter (DSC, ITS-400). The measurements were performed for three concentrations of 0.0731, 0.1914, and 0.4153 mol fraction of 1,2 − propanediol. The expanded uncertainty of the heat capacity (CP), pressure (P), temperature (T), and concentration (x) measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 2.4%, 0.05%, 15 mK, and 0.0001, respectively. The measuredCPPTx data have been used to calculate excess molar heat capacities (CPmE) of the mixture. The second temperature derivatives of specific volume or curvature of the Vm-T isobars have been calculated using the pressure dependence measured heat capacities along the isotherms as ∂2Vm/∂T2Px=-T-1∂CPm/∂PTx. Some unusual behaviour of CP in the low concentration range (below 0.2 mol fraction, dilute mixture) along the each measured isotherms-isobars was found.