Characterization of a Gas Oil Fraction and Its Hydrotreated Products

Abstract

In this work we explore the chemistry of a gas oil fraction in the mid-boiling range (433–483°C) and its products after hydrotreating at 375, 385, and 400°C. Each sample was fractionated by high performance liquid chromatography (HPLC) based on the elution times for saturate, mono-, di-, and poly-aromatic standards. The HPLC saturate fraction is practically free of aromatic components. The nominal mono- and di-aromatics fractions differ in that the former has a higher molecular weight and H/C ratio cbut lower aromaticity and heteroatom content. The H/C atomic ratios, aromaticities, and average structural parameters of the HPLC poly-aromatic subfractions are virtually the same. Regardless of their structural resemblances they differ substantially in their HPLC elution behavior. This can be attributed to the differences in their oxygen and, especially, nitrogen contents. Hydrogenation produced a significantly greater amount of saturate material having a higher H/C ratio than the original feed. A large part of this increase must result from dealkylation, saturation, or opening of aromatic molecules. This mechanism also produced nominally mono-aromatic compounds from the poly-aromatic species originally present. The effect of hydrogenation on heteroatoms was mixed. While the overall amount of nitrogen was reduced, its concentration in the poly-aromatic fractions actually increased. Overall, oxygen concentration in the product was not much affected by hydrogenation, except that its distribution became skewed towards the more easily eluted HPLC front-fractions. Both thiophenic and sulphide sulphur were significantly reduced in all of the separated fractions.