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

Abstract

Flow calorimetric measurements of the excess molar enthaply, H^E_m, 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 H^E_m measurements on methanol–alkane mixtures but when used for methanol–carbon dioxide mixtures the calculated values of H^E_m 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.