Molecular characterization of vitrinite maturation as revealed by flash pyrolysis methods

Abstract

Curie-point pyrolysis - gas chromatography analyses were performed on four vitrinite concentrates of maturity levels from 0.96 %Rmax to 1.93 %Rmax. Analyses were carried out on "thermal extracts" obtained at a Curie-temperature of 358 °C and on pyrolysates obtained at a Curie-temperature of 770 °C. The relative concentrations of alkylphenols and alkylnaphthalenes decrease with increasing maturity. Alkylbenzenes are prominent pyrolysis products throughout the maturity interval investigated. A significant increase in the relative concentration of alkylphenanthrenes and alkylbiphenyls with increasing maturity is noted. There is a substantial similarity between the compositions of "thermal extracts" and pyrolysates. This indicates that the trends observed are mainly due to changes in frequency distributions of extractable compounds. Vitrinite reflectance measurements carried out on the unextracted and extracted concentrates revealed no significant differences with one exception. For one sample, with a maturity approximately at the transition from the "oil window" to the "gas window", solvent extraction resulted in a significantly higher reflectance value of the residue. This sample was rich in extractable n-alkanes.