Examination of the Sooting Tendency of Three-Ring Aromatic Hydrocarbons and Their Saturated Counterparts

Abstract

Hydrotreating of a 1:1 blend of coal-derived refined chemical oil (RCO), with petroleum-derived light cycle oil (LCO), has been identified as a strategy for the production of an advanced coal-based jet fuel, JP-900. The conversion of the jet fuel section of a conventional refinery for the production of coal-based JP-900 would impact the quantity and quality of the other refinery products, such as diesel. The physical and chemical properties of refinery streams may be perturbed by the introduction of coal components into the refinery, including the sooting tendency. A coal-derived diesel cut was chemically analyzed via gas chromatography−mass spectrometry (GC−MS). The results showed that two- and three-ring aromatics and their hydrogenated derivatives comprised the bulk of the cut. Phenanthrene and its hydrogenated derivatives were chosen as representative compounds of this cut. Existing sooting tendency correlations and soot formation indicators in the literature apply to some two-ring aromatic compounds, but little or no information is available about how to predict the sooting tendency of aromatics with three or more rings. The present study provides an analysis of the effects of three-ring aromatic hydrocarbons on soot formation and evaluated how their saturated counterparts contribute to the reduction of the sooting tendency. This research also generated a consistent set of data for smoke point and threshold sooting index (TSI), a parameter proposed for evaluating the onset of soot formation, for three-ring compounds, which have not been reported previously. It was found that the sooting tendency of aromatics is more accurately estimated by investigating their effect on hydrocarbon mixtures rather than as pure compounds. When adding aromatic compounds with the same number of carbon atoms to a reference mixture of 35% (v/v) toluene and 65% (v/v) n-heptane, the most saturated compounds showed the lowest sooting tendency. At small concentrations, three-ring saturated hydrocarbons in fuel blends did not improve the sooting tendency, in contrast to two-ring saturated compounds, which are good hydrogen donors and have low sooting tendency. Finally, the calculated TSI of the mixtures was used to estimate the TSI and smoke points of the individual three-ring compounds contained in the blend using mixing rules.