Diesel quality and molecular structure of bitumen-derived middle distillates

Abstract

Six to seven narrow fractions from each of six light gas oils obtained from various upgrading processes of Athabasca oilsands bitumen were evaluated as diesel fuels. The relationships among the boiling range, cetane number (CN), and aromatics content were investigated. The correlation between CN and aromatic content of narrow-cut fractions showed three trends; i.e. (1) CN increases as aromatics increase; (2) CN decreases as aromatics increase; and (3) a mixed trend of both. In order to investigate such trends, the narrow-cut samples were separated into saturate and aromatic fractions using HPLC, and analyses of type distribution and average molecular structures were carried out. CN of narrow cuts was estimated from the type distribution and CN data for pure compounds. From the H/C atomic ratio, each narrow-cut sample was represented by six types of compounds, i.e. alkanes, mono- and dicycloalkanes, alkyl and naphthenic benzenes, and diaromatics. The average molecular structures for those types had 4–5 branches. The CN trend of the narrow-cuts were reproducible at a certain assumption from the CN of the average molecule structure by type estimated from the CNs of pure compounds. It was found that for the prediction of CN, not only aromatic content but also hydrocarbon types of saturates are important.