Development of simple and transferable molecular models for biodiesel production with the soft-SAFT equation of state

The knowledge of fatty acid esters/biodiesels thermodynamic properties is crucial not only for developing optimal biodiesel production and purification processes, but also for enhancing biodiesels performance in engines. This work is intended to apply a simple but reliable theoretically based sound model, the soft-SAFT EoS, as a tool for the development, design, scale-up, and optimization of biodiesels production and purification processes. A molecular model within the soft-SAFT EoS framework is proposed for the fatty acid esters, and the Density Gradient Theory approach is coupled into soft-SAFT for the description of interfacial properties, while the Free-Volume Theory is used for the calculation of viscosities, in an integrated model. For pressures up to 150 MPa, and in the temperature range 288.15-423.15 K, density, surface tension, viscosity and speed of sound data for fatty acid methyl and ethyl esters, ranging from C_8:0 to C_24:0, with up to three unsaturated bonds, are described with deviations inferior to 5%. Finally, in order to validate the predictive ability of the model to be applied in the biodiesel groundwork, the high pressure densities and viscosities for 8 biodiesels were predicted with the soft-SAFT EoS, reinforcing the validity of the approach to obtain reliable predictions for engineering purposes.