Determination of constant volume heat capacity of mixed supercritical fluids and study on the intermolecular interaction

The constant volume heat capacities (CV) of CO2, propane-CO2, n-pentane-CO2, n-heptane-CO2, acetone-CO2, and ethanol-CO2 were measured at 308.15 K in the pressure range from 6 to 11 MPa, and the concentration of the solutes was 0.5 mol%. The results show that there is a maximum in each CV versus pressure curve which occurs at the pressure where the isothermal compressibility kT is largest. The peak in the CV curve of propane-CO2 is higher than those of n-pentane-CO2 and n-heptane-CO2 mixtures. For the mixtures with polar solutes, the magnitude of the peaks in CV curves is nearly the same although the structure and polarity of the solutes are different. The intermolecular interaction in the mixtures is discussed on the basis of the CV.