Properties and Molecular Structures of Fuel Fractions Obtained from Hydrocracking/isomerization of Fischer-Tropsch Waxes

Abstract

Fuel oils were prepared by hydrocracking/isomerization of Fischer-Tropsch waxes followed by fractionation of product oils. The correlation between the operation conditions and the average molecular structures of fuel oils, and the effect of the average molecular structure of the gas oil fraction on the diesel fuel properties were investigated. The iso-/n-paraffin ratio increased with increased 360°C+ conversion in the gas oil and bottom fractions, increased to a lesser extent in the kerosene fraction, and remained almost constant in the naphtha fraction, regardless of the severity of the hydrocracking/isomerization reaction. Average branching numbers of the isoparaffins were determined by 13C-NMR analysis and compared with the severity of the hydrocracking/isomerization reaction. Average branching numbers of the kerosene and gas oil fractions were nearly constant at approximately 1.3 and 2.0 branch/molecule respectively, but were influenced by 360°C+ conversion in the bottom oil fraction. A linear relationship was obtained between average carbon number and average branching number, suggesting that average branching number can be determined by average carbon number regardless of the severity of the hydrocracking/isomerization reaction. Correlation of the molecular structural parameters of the gas oil fraction with fuel properties such as viscosity, ignition property, and cold flow property showed that the molecular structural formula, (average carbon number) × (n-paraffin ratio)A, had a good linear correlation with the kinematic viscosity (30°C), cetane index, and cold flow plugging point for A = 0.0, 0.02, and 0.05. The molecular structure of the naphtha fraction was also investigated to obtain information such as the position of branching.