14C polyaromatics as radio isotope tracers for grafting analysis during heavy oil pyrolysis

Abstract

Labelled polyaromatics, such as 14C chrysene and 14C acenaphthylene, have been used as tracers during pyrolysis of a heavy oil residue. Prior to this approach the thermal behaviour of 1:1 mixtures of chrysene and Safaniya vacuum residue (VR) were examined using mass spectrometry and ultraviolet (u.v.) analysis. Chrysene was found to be highly reactive, producing dimers and alkylated chrysene materials. From feedstocks with 14C chrysene and 14C acenaphthylene as radio tracers, the distribution of polyaromatics in the pyrolysed heavy oil fractions were determined. In this series, acenaphthylene was found to be more reactive than chrysene in grafting reactions on heavy oil components. The radical quenching propensity of polyaromatic additives towards small radicals has been confirmed, supporting their anticoke effect when used at high concentration. Interestingly, the diluted polyaromatic tracers did not accumulate in the coke fractions. This result points to weak and reversible bonding reactions of the polyaromatic additives onto the heavy oil components.