Generation of adamantanes and diamantanes by thermal cracking of high-molecular-mass saturated fractions of crude oils of different genotypes

The thermal cracking of high-molecular-mass paraffin-cycloparaffin fractions (bp above 350 degrees C) of oils of different genotypes was carried out. Although the >350 degrees C fraction contains neither adamantanes C-10-C-14 nor diamantanes C-14-C-16, which boil in the range 190-286 degrees C, they are generated again during the thermal cracking of high-molecular-mass paraffin-cycloparaffin fractions. Thus, it was first shown that hydrocarbons with the adamantane and diamantane moieties are present in the >350 degrees C fraction. The distribution of C-10-C-13 adamantanes in crude oils correlates well with that in the products of the thermal cracking of high-molecular-mass (>350 degrees C) saturated fractions, thus indicating a relation between the high-molecular-mass hydrocarbon portion containing the adamantane moiety and C-10-C-13 adamantanes in the oils. There is no such correlation for the distribution of diamantane hydrocarbons of the C-14-C-16 series.