Improved Method for Determining the Atmospheric Distillation Curve of Biodiesel Fuels from Reduced Pressure

Vacuum distillation is widely accepted as a useful technique for obtaining the distillation curves of fuels that boil beyond their decomposition temperatures at atmospheric pressure. After their measurement, the obtained curves must be converted to atmospheric-equivalent-temperature curves following the standard method proposed in ASTM D1160. However, this method was originally developed for petroleum-derived hydrocarbons, but not for oxygenated fuels. A specific method to convert reduced-pressure distillation curves of biodiesel fuels to their atmospheric distillation curves is proposed, based on their projection toward a focal point specifically selected for the methyl esters usually composing biodiesel fuels. This projection was made using a generalized Antoine-type equation with Antoine coefficients estimated from a two-parameter correlation as a function of the number of carbon atoms of the original fatty acid and the number of double bonds. The method (named here the Calingaert-like method) is based on the observation that saturation Antonie-type curved lines for pure hydrocarbons converge to a focal point when plotted in the form of log p versus 1/ T and was found to be more accurate than ASTM D1160 method. Another tested method (named here the Cox-like method), based on the convergence of straight lines to a different focal point, was shown to provide intermediate results. Therefore, the Calingaert-like method is proposed as an improved alternative to the ASTM D1160 method for the distillation of biodiesel fuels at reduced pressure.