Study on intermolecular interactions in supercritical fluids by partial molar volume and isothermal compressibility

The apparent densities of H2O–CO2, H2S–CO2, H2–CO2, and CH4–CO2 binary systems were determined at 308.15 K and different pressures. The concentration of the solutes was 0.3 mol%. The partial molar volumes (PMVs) of the solutes and isothermal compressibility of mixed fluids were calculated using the experimental data. The PMVs of the two polar solutes (H2O and H2S) in supercritical CO2 are negative, and a minimum can be observed in each PMV versus pressure curve at the pressure where isothermal compressibility of the fluid is largest. The absolute value of the minimum of H2O is smaller than that of H2S, probably because of the hydrogen bonding between water molecules. However, the PMVs of the two non-polar solutes are positive, and the maximum value of H2 is larger than that of CH4. The effect of molecular size and polarity on the intermolecular interactions between solutes and solvents were discussed.