Modeling of Biodiesel Multicomponent Systems with the Cubic-Plus-Association (CPA) Equation of State

To supply biodiesel with the quality levels required by the standards for alternative fuels, the separation and purification units are extremely important in the biodiesel production plants. The correct knowledge and description of the phase equilibria in systems composed by transesterification products is essential for a correct operation and optimization of the purification process. For that purpose, the cubic-plus-association equation of state (CPA EoS) was here applied to model the phase equilibria of multicomponent systems common to biodiesel production and purification processes. It is shown that the CPA EoS can provide a good description of the liquid-liquid equilibria of multicomponent mixtures containing alcohols, glycerol, and fatty acid esters in the temperature range of operation of the separation units in biodiesel plants. As the liquid-liquid phase equilibrium description depends on the EoS parameters, a discussion is also presented about the best set of parameters and the method to estimate them.