Chemical and Thermophysical Characterization of an Algae-Based Hydrotreated Renewable Diesel Fuel

Second-generation renewable fuels are synthesized through biochemical and thermochemical processes from nonfood biomass feedstock. The resultant fuels are similar to aliphatic synthetic fuels produced through the Fischer–Tropsch process, which contain mainly linear and lightly branched alkanes. We applied the advanced distillation curve method to an algae-based hydrotreated renewable naval distillate fuel (HRD-76) to measure its boiling temperature as a function of distillate volume fraction. Analysis of the bulk fuel sample through nuclear magnetic resonance spectroscopy, gas chromatography, and mass spectrometry showed the principal components to be linear and branched alkanes containing 14–18 carbon atoms. The speed of sound and density of the fuel were estimated from its composition and compared with experimental data measured with a density and sound speed analyzer. The estimates were within 5% of the experimental values. The boiling temperature, density, and composition data were used to estimate the calculated cetane index of the fuel. We also measured the cloud point of the fuel through a constant cooling rate method with optical detection of paraffin wax precipitation. The measured cloud point was consistent with reported values for hydrotreated renewable fuels, which tend to be higher than cloud points of diesel fuels derived from petroleum. The quantitative thermophysical and chemical data can be used to improve combustion modeling of HRD-76 and other second-generation renewable fuels.