A study of organic sulphur compounds in the pyrolyzate of the Vrelo kerogen (the Dinarides, Croatia)

Abstract

In order to study organic sulphur compounds in the Vrelo kerogen (Upper Jurassic source rock taken from the Dinarides), “off-line” pyrolysis was applied. For the purpose of identification, the pyrolysis was carried out at 550 °C for 15 min in a stream of nitrogen, and volatile products were obsorbed in n-hexane as well as in decahydronaphhalene, both cooled to −30 °C. The pyrolysis product of kerogen is an extremely complex mixture. It was studied by gas chromatography and gas chromatography/mass spectrometry. Besides saturated hydrocarbons, unsaturated hydrocarbons and aromatics, the following organic sulphur compounds have been determined: thiophene, alkylated thiophenes, alkenylthiophenes, benzothiophene and alkylated benzothiophenes. The alkylated thiophenes are dominated by a limited number of isomers. The identified alkylthiophenes have a low molecular weight. The kerogen type for the Vrelo sample was determined by the thiophene ratio 2,3-dimethylthiophene /( n-non-1-ene + 1,2-dimethylbenzene) and it showed the Vrelo kerogen to be of type II-S, kerogen with a high organic sulphur content which is expected to produce high-sulphur oils. The high organic sulphur content indicates anoxic environment conditions, poor in iron ions, at the time when the related organic facies precursor was deposited.