Structural Analysis of Petroleum Derived Heavy Oils and Their Cracking Properties.

Abstract

For the purpose to provide some insight into the relationship between structural characteristics of petroleum derived heavy oils and their thermal- and hydro-cracking properties, structural characterization of some deasphalted oil (DAO) and asphaltene (ASP) samples by means of chromatographic separation followed by NMR and elemental analyses, and Curie-point pyrolysis and catalytic hydrotreatment of the oils and their fractions were carried out. The principal results are summarized as follows: (a) In the Curie-point pyrolysis investigation, it was found that a saturates fraction from specific DAO sample, which contained a considerable amount of naphthenic compounds, could suppress coke formation from aromatic and polar compounds fractions of DAO, whereas such an effect was not observed in the case of other saturates fractions consisted mainly of straight paraffins. It was proposed that the effect of naphthenic components was due to their hydrogen donating property. (b) Addition of a light hydrocarbon solvent, such as cyclohexane or benzene, in the hydrotreatment of an asphalt fraction using Ni-Mo/Al 2 O 3 was found to significantly enhance desulfurization as well as cracking of heavier components in the sample. This is thought to be attributable to the supercritical effect of the solvents. (c) Analyses of the oils obtained by individual hydrotreatment of polyaromatics, polar compounds, and asphaltene fractions from a heavy end, indicated that they contained significantly similar saturates, monoaromatics, and diaromatics components, suggesting that the fractions before the treatment have mutually resembling structure moieties. Meanwhile, the conversion of the starting fractions to the less polar and less aromatized fractions normally decreased in the order polyaromatics>polar compounds>asphaltene.