The influence of pure compounds’ parameters on the phase behaviour of carbon dioxide + 1-hexanol binary system

New vapour–liquid–liquid and vapour–liquid equilibrium data to complement the existing ones are measured at six temperatures (308.15 K to 383.15 K) and at pressures up to 182.9 K using an analytic-static method with phases sampling via special valves (“AnTVisVarCap”, as defined by Prof. Ralf Dohrn and co-workers) for the carbon dioxide (1) + 1-hexanol (2) binary system. Four out of the six isotherm reported here are measured for the first time. The main component of the high-pressure setup is a 60 cm³ visual cell.

The new isotherms are compared with the available literature which is also reviewed and analysed. It should be noted that among the data already published, only one other research group reported the compositions of both phases at equilibrium, as we did previously by using another experimental method. The new and literature data were modelled with Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state based on a semi-predictive procedure to reproduce as well as possible the minimum and the maximum of the critical curve(s) using one set of binary interaction parameters. The influence of critical data and acentric factors of pure components on the phase behaviour of their binary system is discussed. Although the values of the critical pressures and acentric factors of pure substances are not very different in the database we used, the models predict type III or IV phase behaviour with the same set of binary interaction parameters. This sensitivity, which was not observed for other systems we studied, could be explained by the alcohol structure and high asymmetry of the system. Therefore, we analysed in more depth the influence of the critical temperatures and pressures, as well as the acentric factors of carbon dioxide and 1-hexanol and exemplified for one temperature located above the system UCEP's temperature.