Phase equilibria of glycerol containing systems and their description with the Cubic-Plus-Association (CPA) Equation of State

Biodiesel is nowadays in Europe the most used biofuel for road transportation. During its production, different separation and purification processes are required for the glycerol rich streams such as the recovery of the unreacted alcohol and the removal of water. The adequate design of the recovery and purification steps requires the knowledge about the vapour-liquid equilibria data for water + glycerol and alcohol + glycerol systems that are surprisingly scarce. To overcome this lack of information, experimental measurements for 5 alcohol + glycerol systems were performed. These data were used to evaluate the capability of the Cubic-Plus-Association Equation of State (CPA EoS) to model systems containing glycerol. To achieve a good description of the experimental data a new association scheme is proposed for the glycerol molecule. It is shown that a very good description of the VLE data with average deviations inferior to 1% for the bubble point temperatures is obtained. Two different cross-associating combining rules were tested with similar results. Furthermore the predictive performance of the model is evaluated for multicomponent systems. Good liquid-liquid equilibria predictions are obtained for the ternary system methanol + glycerol + methyl oleate at four different temperatures.