Methanol: Association behaviour, third-law entropy analysis and determination of the enthalpy of formation

Chemical equilibrium constants for the methanol from CO/H 2 reaction calculated from literature ther- modynamic parameters are too high as compared to experimental results. Therefore, both the entropy value and the enthalpy of formation value of methanol were reviewed. A rigorous analysis of the associa- tion behaviour of methanol vapour confirms that dimers and cyclic tetramers play an important role, but physical non-ideal gas behaviour must also be taken into account. Accurate relationships for the asso- ciation equilibrium constants and the physical contribution to the second virial coefficient were derived with the use of a combined fit of multiple experimental data sources including heat capacity, speed of sound, thermal conductivity, excess molar enthalpy of methanol and nitrogen and heat of vaporization. Additionally, high temperature second virial coefficients and measures for the consistent temperature de- pendencies of the entropy and enthalpy of formation were included in the parameter optimization to support the accuracy of the model. All experimental results and supporting data were taken or derived from the literature. The resulting virial equation of state was used to calculate new ideal-gas entropy and enthalpy of formation values of methanol, which now turn out to be consistent with values derived from experimental chemical equilibrium data. Furthermore, the new third-law entropy value turns out to be consistent with the current literature value. A new enthalpy of formation value is recommended and an improved chemical equilibrium relationship for the methanol from CO/H 2 reaction is presented.