ISSN 0965-5441, Petroleum Chemistry, 2016, Vol. 56, No. 8, pp. 672–676. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © G.N. Gordadze, M.V. Giruts, A.R. Poshibaeva, V.N. Koshelev, 2016, published in Neftekhimiya, 2016, Vol. 56, No. 5, pp. 443–447.
The Formation Features of C10–C20 Regular Petroleum Isoprenanes
G. N. Gordadze*, M. V. Giruts, A. R. Poshibaeva, and V. N. Koshelev
Gubkin Russian State University of Oil and Gas (National Research University), Moscow, Russia
*e-mail: gordadze@rambler.ru
Received March 24, 2016
Abstract—To model the formation processes of C10–C20 petroleum isoprenanes, thermolysis of regular and
irregular C20–C40 isoprenanes (phytane, crocetane, squalane, and lycopane) and the suggested precursors of
regular petroleum isoprenanes (phytol and isophytol) has been conducted. It has been shown that the ther-
molysis of these compounds results in the formation of regular, irregular, and pseudoregular isoprenanes; the
trends in their distribution have been revealed; and the retention indices have been determined. It has been
assumed that the pristane/phytane ratio, which is used in petroleum geochemistry, should be treated with
caution.
Keywords: regular, irregular, and pseudoregular petroleum isoprenanes, thermolysis
DOI: 10.1134/S0965544116080077
Aliphatic petroleum isoprenanes have regular, prenoid acids, such as farnezanic and phytanic acids,
irregular, and pseudoregular carbon chains with which are found in a large amount in a variety of par-
the number of carbon atoms of 9 to 45 [1–5]. Iso- affinic oils [10]. The process of formation of iso-
prenanes are known to consist of isoprene (2-methyl- prenoid alkanes from isoprenoid acids is apparently
the same as the process of conversion of fatty acids
into n-alkanes. Isoprenanes are also formed by the
thermolysis of kerogen, petroleum asphaltenes and
resins, and rock organic matter [11, 12]. Recently, we
have found that bacterial metabolites contain regular
C17 isoprenane along with other regular isoprenanes
and suggested that it could be formed from squalene,
which has also been found in the soluble part of the
bacterial biomass [13, 14].
We are aware that the identification of the forma-
tion routes of petroleum hydrocarbons (HCs), in par-
ticular, isoprenanes is a very complicated process. The
difficulty is due both to the composition and structure
of the original OM and to various geochemical envi-
ronments of OM transformation to hydrocarbons.
However, it is obvious that regular C10–C20 petroleum
isoprenanes (including pristane and phytane, the ratio
of which is considered a genetic indicator) can be gen-
erated not only from the fatty (lipid) material (acids,
esters of saturated and unsaturated fatty acids) occur-
ring in marine and/or continental sediments, but also
from the high-molecular-mass hydrocarbons regular
and irregular isoprenanes as a result of their thermal
transformations.
butadiene-1,3) units, which can be connected in the
“head-to-tail” mode called regular or in the “tail-to-
head” and “tail-to-tail” modes in one molecule to
make it named irregular. Pseudoregular isoprenanes
are formed from irregular ones in the case if the C–C
bond breaking site is in the region of the irregular unit.
As a rule, regular isoprenanes prevail in crude oils,
condensates, coals, and dispersed organic matter
(OM) of rocks. Note that all caustobioliths contain the
homologous series of regular isoprenanes to C20 and
do not contain C12 and C17 isoprenanes. It is believed
that regular isoprenanes in crude oils were derived
from phytol (unsaturated C20 alcohol with the regular
isoprenane structure as a side chain of chlorophyll)
[4–7] and the absence of C12 and C17 isoprenanes is
due to a low probability of the simultaneous rupture of
two C–C bonds at the tertiary carbon atom. It is also
believed that phytane or 2,6,10,14-tetramethylhexade-
cane is formed if phytol gets into mainly reducing
environment (the number of carbon atoms in the iso-
prenane chain is preserved) and, getting into oxidizing
environment, phytol is oxidized to phytolic acid,
which is subsequently decarboxylated to give the regu-
lar isoprenane pristane (2,6,10,14-tetramethylpenta-
decane) having one carbon atom less. Furthermore,
some scientists associate high concentrations of pris-
tane with the presence of this hydrocarbon in appre-
ciable amounts in biomass of various kinds, in partic-
ular, zooplankton lipids [8, 9]. A certain amount of
isoprenoid structures can be produced from iso-
EXPERIMENTAL
As the initial objects of research we selected the
regular isoprenane C20 phytane (2,6,10,14-tetrameth-
ylhexadecane); the irregular isoprenanes C20 croce-
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