Vanadyl porphyrins were isolated from Yakutiya oil shale bitumens and also from kerogen and bitumen pyrolysates. They were analysed by mass spectrometry, HPLC and 1H NMR. The oil shales investigated were all from the same formation (Cambrian) but from samples containing different kerogen types. Samples ranged in maturity from Ro = 0.5 to 0.7. Bitumens extracted from the shales, with a value of Ro = 0.5 contained mainly DPEP porphyrins, that is chlorophyll α (C31D and C32D) and chlorophyll c (C30D) derivatives. Shales containing different kerogen types gave different DPEP/ETIO,C1 30E/C2 30E and C30D/C32D ratios. As pyrolysis temperatures were increased to 370°C, the difference between the released products disappeared. Heating bitumens isolated from oil shales with Ro values = 0.5 resulted in a decrease in the total porphyrin yield and in the DPEP/ETIO ratio. Also, heating at relatively low temperatures (270°C) leads to alkylation of the pigments, whereas heating at higher temperatures (370°C) causes dealkylation of the porphyrins. The composition of the vanadyl porphyrins in the extracted bitumens of oil shale with an Ro value of 0.70 are identical to those observed in the products of bitumen (Ro = 0.5) thermolysis at 370°C.
ASJC Scopus subject areas
- Geochemistry and Petrology