Effect of phase behavior on the constant volume heat capacity of ethane + ethanol and ethane + acetone mixed fluids near the critical region and the intermolecular interaction

The phase behaviors, constant volume heat capacity (Cv), and isothermal compressibility (KT) of ethane+ethanol and ethane+acetone binary mixtures have been measured in supercritical (SC) region and subcritical region near the critical point (CP) of the mixtures at 309.45 K. The experiments have also been carried at the conditions far from the critical point of the mixtures. It is demonstrated that in supercritical region there exists a maximum in Cv versus pressure curve (Cvmax) at fixed composition, which occurs at the pressure where KT is the largest. In subcritical region, Cv and KT increase sharply as pressure approaches the critical point or bubble point (BP), and the Cv at CP or BP can be several times larger than that of the fluids far from the phase separation pressures. On the basis of the experimental results, the intermolecular interaction is discussed.