The distribution of sulfur compounds in hydrotreated jet fuels: Implications for obtaining low-sulfur petroleum fractions

Abstract

The mechanism by which jet fuels are hydrotreated to reduce sulfur levels has some important implications in terms of the species and distribution of sulfur compounds remaining in the fuel. The species of sulfur that are most difficult to remove by hydrotreating, such as benzothiophenes and methyl- and dimethyl-benzothiophenes, are concentrated in the higher-boiling fraction of the fuel. Consequently, the lower-boiling fractions of the fuel contain much less sulfur. It may be possible, therefore, to obtain petroleum fractions that contain low levels of sulfur simply by distillation of the jet fuel into low-boiling and high-boiling fractions. A multi-element simulated distillation procedure according to ASTM D-2887, standard test method for boiling range distribution of petroleum fractions by gas chromatography, was coupled with atomic emission detection (GC-AED) and was used to estimate the sulfur concentration in various fractions of jet fuel, namely 20, 50, and 60%. The estimations of sulfur concentration were verified by comparing them to analyzed sulfur concentrations in several fractions of physical distillations of the jet fuels according to a modified ASTM D-86, standard test method for distillation of petroleum products at atmospheric pressure. Sulfur analyses showed that for all fuels analyzed, the initial 20% boiling fraction of the fuel contained no more than approximately 5% of the total sulfur concentration. The initial 50% boiling fraction of the fuel contained no more than 25% of the total sulfur concentration, and in most cases contained significantly less (8–16%). The total concentration of sulfur in the jet fuels tested ranged from 260 to 1380 μg/g, and there did not appear to be a direct relationship between total sulfur concentration and percentage of sulfur in each jet fuel boiling fraction.