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 C8:0 to C24:0, 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.