Hydrocarbon Renewable and Synthetic Diesel Fuel Blendstocks: Composition and Properties

We examined the chemical composition and properties of several diesel fuels and blendstocks derived from Fischer-Tropsch (FT) synthesis, hydroisomerization of lipids, and fermentation of sugar via the terpenoid metabolic pathway. Comprehensive two-dimensional gas chromatographic analysis with nonpolar and polar columns, C-13 NMR, GC-MS, and elemental analysis were used to assess fuel chemistry. Performance properties included density, heat of combustion, cetane number, and cloud point, as well as other properties. The fuels consisted almost entirely of normal and iso-paraffins. Three samples contained residual oxygen below 0.1 mass %. All of the renewable and synthetic diesel fuels have significantly lower density than is typical for a petroleum-derived diesel fuel. As a result, they have slightly higher net heat of combustion on a mass basis (2%-3% higher), but lower heat of combustion on a volume basis (3%-7% lower). Two critical diesel performance properties, cetane number and cloud point, were correlated with iso-paraffin content and chain length. The results confirm that properties of hydroisomerized fats and oils, as well as FT diesel, can be tuned by increasing the degree of isomerization to lower cloud point which also lowers the cetane number. In spite of this trade-off between cloud point, and cetane number, the cetane numbers were still over 70 for fuels with cloud points as low as -27 degrees C. The terpenoid biofuel exhibited a cloud point below -70 degrees C and a cetane number of 58.