25th International Meeting on Organic Geochemistry IMOG 2011

P-034
Chemical structure of kerogen before and after hydrous
pyrolysis
Nadezhda Burdelnaya 1 , Dmitry Bushnev 1 , Maxim Mokeev 2 , Alexsander Gribanov 2
1 Insitute of Geology of Komi SC of RAS, Syktyvkar, Russian Federation, 2 Institute of Macromolecular
Compounds of RAS, Saint-Petersburg, Russian Federation (corresponding
author:burdelnaya@geo.komisc.ru)
The natural organic matter (OM) maturation is a
long process inaccessible to direct observation. In
laboratory conditions at stage-by-stage growth of
temperature it is possible to simulate the process of
artificial OM maturation and to track changes in the
structure of kerogen.
To carry out the hydrous pyrolysis experiments we
chose samples of different type of kerogen (I, II, II-S
and III). The samples were Estonian kukersite (type I);
the Upper Jurassic oil shales from the Sysolsky shale
area (type II and II-S); Oxford and Domanik
carbonaceous shales (type II); coal of the Nechensky
deposit (type III). Pieces of rocks (by 25 g) were put in
autoclave, and 20 ml of distilled water was added.
The thermolysis was performed by 24 h at
temperature 300 о С. The bitumen was extracted by
chloroform, then kerogen was isolated from the rock.
The of bitumen content, Corg, elemental composition
of kerogen were determined before and after hydrous
pyrolysis. NMR high resolution spectra was received
at spectrometer BRUKER AVANCE II-500 (frequency
at 13 С – 125.77 MHz).
All types of kerogen lost hydrogen and oxygen that
is expressed in decrease in H/C and O/C ratios.
Kerogen types II and II-S are characterized by
sharper decrease of Corg and loss of aliphatic
structures (H/C sharply drops). The maximum yield of
bitumen was received in the Volga shales with high
content of sulfur organic structures in kerogen
(kerogen type II-S).
According to solid state 13 С NMR spectroscopy
significant changes in kerogen structure after the
experiment were observed in Jurassic samples (type
II and II-S). The most intensive signal in 13 С NMR
spectrum of all samples is in area 10 - 45 ppm, which
corresponds to absorption of carbon of methyl,
methylene groups, and also tertiary and quaternary
atom of carbon. The highest concentration of aliphatic
carbon is related to kerogen of kukersite with
prevalence of methylene carbon of n-alkyl chain. After
heat treatment the structure of aliphatic chains does
not change practically. Considering spectra of
kerogen type II С-6/9, М-1/2, D-1/30 it is possible to
testify the results in favor of the relation of spectral
pattern of their aliphatic and aromatic structural units.
After autoclaving significant changes in transformation
of chemical structure of kerogen in these samples are
observed, but these changes proceed in one
direction, and it is connected to the increasing
concentration of aromatic nuclea in geopolymer. It is
expressed in increasing signal intensity in band 100 -
160 ppm, a special signal at 127 ppm, corresponding
to chemical shift of protonated carbon in aromatic
rings. The Caliph/Carom ratio in the specified samples -
М-1/2, С-6/9, D-1/30 and V-1/5 tends to one. In the
spectrum of coal kerogen before heat treatment three
intensive signals in band from 100 to 160 ppm are
determined, which are characteristic for carbon in
aromatic structures. After hydrous pyrolysis of rocks
the signal sharply increases at 127 ppm, which
intensity is more than 50% from intensity of other
signals. Probably, there is a rearrangement of mono-,
bycyclic systems into a more compact condensed
polyaromatic structure, which is simultaneously
accompanied by aromatization of acyclic and cyclic
methylene chains and loss of methyl groups.
Nevertheless, the Caliph/Carom ratio, which is less than
one after hydrous thermolysis, changes insignificantly.
Strong changes in the ratio of aliphatic and aromatic
groups were determined in kerogen of type II-S. If the
considered ratio before heat treatment was 3.9, then
after aqueous thermolysis we observed sharp loss of
aliphatic units and aromatization of chemical structure
of kerogen.
The available data confirms non-uniform thermal
influence on structural change of the organic matter
characterized by various types of kerogen. Direct
studying of kerogen structure by solid state 13 С NMR
spectroscopy showed that aqueous thermolysis at
300 о С equally influences on the change of chemical
structure of OM types II and II-S. These changes are
not as noticeable for types I and III due to features of
their chemical structure of kerogen.
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