Directory UMM :Data Elmu:jurnal:O:Organic Geochemistry:Vol31.Issue12.Dec2000:
Organic Geochemistry 31 (2000) 1783±1795
www.elsevier.nl/locate/orggeochem
CS2/NMP extraction of immature source rock concentrates
Guo Shaohui *, Li Shuyuan, Qin Kuangzong
State Key Lab of Heavy Oil Processing, University of Petroleum, 102200, China
Abstract
Eleven Chinese immature source rock concentrates from the immature oil formations in four dierent depressions
were extracted ultrasonically with a mixture of CS2 and N-methyl-2-pyrrolidinone (CS2/NMP) at room temperature.
The samples were also extracted with CHCl3 and a mixture of methanol/acetone/chloroform (MAC) for comparison.
The solvent system CS2/NMP is very ecient for the extraction of immature source rock concentrates, giving much
higher extraction yields than CHCl3 or MAC. The composition of the extracts using dierent solvent mixtures is also
dierent. Model compound tests indicate that no chemical reactions have taken place between the NMP and the substrates in the extraction. These results suggest that there are abundant non-covalent bond interactions in the organic
matter of the immature source rock concentrates. The fact that CS2/NMP mixed solvent extracts more than MAC and
CHCl3 is not only because it can dissolve higher molecular weight fractions, but also because it has stronger ability to
disrupt the complex interactions existing between the soluble and insoluble fractions. Biomarker distributions in the
saturated hydrocarbon fractions are dierent for dierent solvent systems, suggesting that care should be taken when
comparing the biomarker parameters in source rocks when using dierent solvents for extraction. # 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: Source rock concentrate; Immature source rock; Solvent extraction; CS2/NMP; Methanol/acetone/chloroform; Chloroform
1. Introduction
Although characterization of solvent extracts is a
promising approach to the clari®cation of organic
structure in geological macromolecules, the extraction
yields by conventional solvents under mild conditions is
often too low to get valuable information. It is of great
value to determine the quantity of extractable substances
in source rocks and coals, which is closely related with
the debatable concept of the mobile phase (component)
and rigid phase (network) in coal structures (Derbyshire
et al., 1989). Many studies on solvent extraction have
been reported (Pullen, 1981), but they have been mostly
by Soxhlet extraction carried out using conventional
solvents at temperatures near the boiling point of the
solvent. Chemical reactions such as decomposition and
oxidation, may occur in certain cases, especially for
solvents with high boiling points. A ternary azotrope of
chloroform, methanol, and acetone (MAC, 47:23:30 by
* Corresponding author.
weight, bp 57.5 C) has been used for extracting biological
markers and other soluble materials from coal macerals
and other organic sediments (Allan et al., 1977; Given,
1984). Allan et al. (1977) used this mixture to extract 9±
17% by weight of eight vitrinite concentrates (77±84%
C, daf) and 2% from two vitrinites of high rank coals
(85.5, 86.7% C). The yield of extract from 10 sporinite
concentrates was 4±6%. Solvent extraction under mild
conditions, which causes little chemical change to substrates extracted, provides valuable information on their
structures through characterization of the extract and
residue and clari®cation of the extraction mechanisms.
There are few studies of extraction of source rocks
at room temperature, since it usually gives low
yields. It has been found that a mixed solvent of CS2
and N-methyl-2-pyrrolidinone (CS2/NMP) is a powerful
solvent at room temperature for the extraction of bituminous coals (Iino et al., 1988) to give extracts characteristic
of the original organic macromolecules.
A number of reports indicate that N-methyl-2-pyrrolidinone is chemically inert during extraction and does
not react with the extracted coals (Iino, et al., 1988;
0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0146-6380(00)00126-1
1784
G. Shaohui et al. / Organic Geochemistry 31 (2000) 1783±1795
Seehra et al., 1988; Cagniant et al., 1990; Pajak et al.,
1994; Chervenick and Smart, 1995). Cagniant et al.
(1990) concluded that NMP did not react with extracted
coals, and a series of model compounds, using boiling
NMP (202 C) under a nitrogen atmosphere. These
model compounds are representative of the main compounds containing functional groups in coals: they
include dibenzyl ether, phenyl and benzyl benzoates,
dibenzofuran, diphenyl sul®de, diphenyl methane and
phenol. Alternatively, Cai and Smart (1993) concluded
that NMP is reactive with coal and is responsible for
breaking carbon±oxygen bonds when used at its boiling
point under nitrogen. They also concluded that during
NMP-coal extraction, it may be able to break carbon±
oxygen bonds when used at its boiling point. White et
al. (1997) suspected that a hydroperoxide may be an
intermediate in the reaction of NMP with oxygen to
yield N-methylsuccinimide and that the hydroperoxide
could initiate the oxidation of other substrates during
extraction at the boiling point of NMP. Although it
cannot be stated explicitly that there are no reactions
between NMP and the substrates extracted under certain
extraction conditions, no one has reported, until now,
that chemical reactions occur between NMP and the
organic substrates extracted under room temperature
conditions. Use of this mixed solvent for source rock
and coal extraction thus seems to be an eective means
of increasing the yield without disrupting the chemical
structure of the macromolecules.
This study is concerned with an investigation of the
CHCl3, methanol/acetone/chloroform (MAC, 23:30:47
by weight) and CS2/NMP (1:1 by volume) mixed solvent
extractability, and the solvent-soluble components, of
the organic matter (OM) in Chinese immature source
rocks. As oil exploration continues, more and more
immature oil has been recovered. Currently, immature
oil production accounts for nearly 10% of the total
production in China. Although several mechanisms for
the formation of immature oil have been proposed
(Lane and Jackson, 1980; Snowdon and Powell, 1982;
Orr, 1986; Khorasani, 1987; Khorasani and Michelsen,
1991; Snowdon, 1991), there are still many questions to
be answered. Therefore, only immature source rocks were
studied in this work. Extraction of model compounds with
NMP was also carried out to test if chemical reactions
take place.
2. Experimental
2.1. Materials and pretreatment
Eleven Chinese immature source rock samples were
selected from immature oil formations in four dierent
depressions. Three source rock samples were taken from
well Dai-6 (D-6), well Wangsi 8-2 (WS8-2) and well
Zhouxie 22-1 (ZX22-1) in the Qianjiang depression of
the Jianghan basin. One sample was from well Tong-29
(T-29) in the Dongying depression. Three samples from
the East-Liaohe depression were from wells To-12 (To-12),
To-16 (To-16) and To-20 (T-20). Four samples from the
West-Liaohe depression were taken from wells Du-22
(D-22), Gao-60 (G-60), Lei-15 (L-15) and Lei-36 (L-36).
Source rock samples were ground to
www.elsevier.nl/locate/orggeochem
CS2/NMP extraction of immature source rock concentrates
Guo Shaohui *, Li Shuyuan, Qin Kuangzong
State Key Lab of Heavy Oil Processing, University of Petroleum, 102200, China
Abstract
Eleven Chinese immature source rock concentrates from the immature oil formations in four dierent depressions
were extracted ultrasonically with a mixture of CS2 and N-methyl-2-pyrrolidinone (CS2/NMP) at room temperature.
The samples were also extracted with CHCl3 and a mixture of methanol/acetone/chloroform (MAC) for comparison.
The solvent system CS2/NMP is very ecient for the extraction of immature source rock concentrates, giving much
higher extraction yields than CHCl3 or MAC. The composition of the extracts using dierent solvent mixtures is also
dierent. Model compound tests indicate that no chemical reactions have taken place between the NMP and the substrates in the extraction. These results suggest that there are abundant non-covalent bond interactions in the organic
matter of the immature source rock concentrates. The fact that CS2/NMP mixed solvent extracts more than MAC and
CHCl3 is not only because it can dissolve higher molecular weight fractions, but also because it has stronger ability to
disrupt the complex interactions existing between the soluble and insoluble fractions. Biomarker distributions in the
saturated hydrocarbon fractions are dierent for dierent solvent systems, suggesting that care should be taken when
comparing the biomarker parameters in source rocks when using dierent solvents for extraction. # 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: Source rock concentrate; Immature source rock; Solvent extraction; CS2/NMP; Methanol/acetone/chloroform; Chloroform
1. Introduction
Although characterization of solvent extracts is a
promising approach to the clari®cation of organic
structure in geological macromolecules, the extraction
yields by conventional solvents under mild conditions is
often too low to get valuable information. It is of great
value to determine the quantity of extractable substances
in source rocks and coals, which is closely related with
the debatable concept of the mobile phase (component)
and rigid phase (network) in coal structures (Derbyshire
et al., 1989). Many studies on solvent extraction have
been reported (Pullen, 1981), but they have been mostly
by Soxhlet extraction carried out using conventional
solvents at temperatures near the boiling point of the
solvent. Chemical reactions such as decomposition and
oxidation, may occur in certain cases, especially for
solvents with high boiling points. A ternary azotrope of
chloroform, methanol, and acetone (MAC, 47:23:30 by
* Corresponding author.
weight, bp 57.5 C) has been used for extracting biological
markers and other soluble materials from coal macerals
and other organic sediments (Allan et al., 1977; Given,
1984). Allan et al. (1977) used this mixture to extract 9±
17% by weight of eight vitrinite concentrates (77±84%
C, daf) and 2% from two vitrinites of high rank coals
(85.5, 86.7% C). The yield of extract from 10 sporinite
concentrates was 4±6%. Solvent extraction under mild
conditions, which causes little chemical change to substrates extracted, provides valuable information on their
structures through characterization of the extract and
residue and clari®cation of the extraction mechanisms.
There are few studies of extraction of source rocks
at room temperature, since it usually gives low
yields. It has been found that a mixed solvent of CS2
and N-methyl-2-pyrrolidinone (CS2/NMP) is a powerful
solvent at room temperature for the extraction of bituminous coals (Iino et al., 1988) to give extracts characteristic
of the original organic macromolecules.
A number of reports indicate that N-methyl-2-pyrrolidinone is chemically inert during extraction and does
not react with the extracted coals (Iino, et al., 1988;
0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0146-6380(00)00126-1
1784
G. Shaohui et al. / Organic Geochemistry 31 (2000) 1783±1795
Seehra et al., 1988; Cagniant et al., 1990; Pajak et al.,
1994; Chervenick and Smart, 1995). Cagniant et al.
(1990) concluded that NMP did not react with extracted
coals, and a series of model compounds, using boiling
NMP (202 C) under a nitrogen atmosphere. These
model compounds are representative of the main compounds containing functional groups in coals: they
include dibenzyl ether, phenyl and benzyl benzoates,
dibenzofuran, diphenyl sul®de, diphenyl methane and
phenol. Alternatively, Cai and Smart (1993) concluded
that NMP is reactive with coal and is responsible for
breaking carbon±oxygen bonds when used at its boiling
point under nitrogen. They also concluded that during
NMP-coal extraction, it may be able to break carbon±
oxygen bonds when used at its boiling point. White et
al. (1997) suspected that a hydroperoxide may be an
intermediate in the reaction of NMP with oxygen to
yield N-methylsuccinimide and that the hydroperoxide
could initiate the oxidation of other substrates during
extraction at the boiling point of NMP. Although it
cannot be stated explicitly that there are no reactions
between NMP and the substrates extracted under certain
extraction conditions, no one has reported, until now,
that chemical reactions occur between NMP and the
organic substrates extracted under room temperature
conditions. Use of this mixed solvent for source rock
and coal extraction thus seems to be an eective means
of increasing the yield without disrupting the chemical
structure of the macromolecules.
This study is concerned with an investigation of the
CHCl3, methanol/acetone/chloroform (MAC, 23:30:47
by weight) and CS2/NMP (1:1 by volume) mixed solvent
extractability, and the solvent-soluble components, of
the organic matter (OM) in Chinese immature source
rocks. As oil exploration continues, more and more
immature oil has been recovered. Currently, immature
oil production accounts for nearly 10% of the total
production in China. Although several mechanisms for
the formation of immature oil have been proposed
(Lane and Jackson, 1980; Snowdon and Powell, 1982;
Orr, 1986; Khorasani, 1987; Khorasani and Michelsen,
1991; Snowdon, 1991), there are still many questions to
be answered. Therefore, only immature source rocks were
studied in this work. Extraction of model compounds with
NMP was also carried out to test if chemical reactions
take place.
2. Experimental
2.1. Materials and pretreatment
Eleven Chinese immature source rock samples were
selected from immature oil formations in four dierent
depressions. Three source rock samples were taken from
well Dai-6 (D-6), well Wangsi 8-2 (WS8-2) and well
Zhouxie 22-1 (ZX22-1) in the Qianjiang depression of
the Jianghan basin. One sample was from well Tong-29
(T-29) in the Dongying depression. Three samples from
the East-Liaohe depression were from wells To-12 (To-12),
To-16 (To-16) and To-20 (T-20). Four samples from the
West-Liaohe depression were taken from wells Du-22
(D-22), Gao-60 (G-60), Lei-15 (L-15) and Lei-36 (L-36).
Source rock samples were ground to