Characterization of asphaltenes by pyrolysis and chromatography

Abstract

Asphaltenes comprise the fraction of crude oil that is insoluble in light saturated hydrocarbons. They are macromolecules consisting of condensed, essentially aromatic, nuclei bearing side-chains of variable lengths and occasionally bridged by heteroatoms. The objective of this work was to study asphaltenes by pyrolysis—chromatographic techniques. The pyrolysis conditions must be adjusted so that they provide the best information on the moieties comprising the asphaltenes. Moreover, the conditions must be such that they limit the recombination of the radicals generated; this presupposes a sufficient dilution and rapid quenching of the products formed during pyrolysis. The first results indicate good reproducibility with respect to both the amounts obtained and the gas chromatographic fingerprints. The pyrograms show that the distribution of n-alkanes obtained by pyrolysis of asphaltenes ranges up to C 30 and is very similar to the n-alkane distributions in the corresponding crude oils. It therefore seems possible to study biodegraded crude oils in which n-alkanes have disappeared by studying asphaltenes using pyrolytic methods.