Excess molar enthalpies of (methanol–carbon dioxide)(g) from 448.2 to 548.2 K at pressures up to 15 MPa

Flow calorimetric measurements of the excess molar enthaply, HEm, of [0.5CH3OH–0.5CO2](g) are reported. The measurements extend over the temperature range 448.2 to 548.2 K and at pressures up to 15 MPa. A modification of the equation of state proposed by Kubic was used to fit the measurements. This equation was previously used successfully to fit HEm measurements on methanol–alkane mixtures but when used for methanol–carbon dioxide mixtures the calculated values of HEm were too large. The difference between the calculated and experimental values was attributed to a weak specific interaction between methanol and carbon dioxide. Analysis of the measurements using a further modification of the Kubic equation which includes terms to account for the methanol–carbon dioxide association yields a value of the equilibrium constant, K12(298.15 K)= 0.056 MPa–1, and a value of the enthalpy of association, ΔH12=–13.9 kJ mol–1. These values are similar to those found previously for the water–carbon dioxide interaction.