Characterisation and differentiation of kerogens by pyrolytic and chemical degradation techniques

The structural characterization of a set of kerogen concentrates belonging to the three well differentiated conventional main types (I, II, III) has been undertaken by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) both in the absence and presence of tetramethylammonium hydroxide (TMAH). The results obtained have been compared to the structural features as discerned by chemical degradative methods (KMnO4 or RuO4 oxidation, hydrolysis with phase transfer catalyst and transalkylation reactions) and solid state C-13-NMR spectroscopy. The compounds released upon conventional pyrolysis were mainly saturated and olefinic hydrocarbons for the type I and II kerogen samples, whereas aromatic compounds were predominant in the kerogen of type III, in agreement with KMnO4 oxidation data and the NMR spectra. Pyrolysis/TMAH released relatively high amounts of saturated and unsaturated unbranched mono- and dicarboxylic acids (as their methyl esters) from all the samples, as well as minor amounts of aromatic acids (as their methyl esters), which indicates that considerable amounts of functionalized compounds are bound to the macromolecular structure via ester or ether linkages. Overall, Py/TMAH and chemical degradations give complementary results concerning the chemical nature of the released fatty acid series identified. (C) 2001 Elsevier Science B.V. All rights reserved.