Hydrous pyrolysis of methylphenanthrenes - Degradation and isomerization

Article abstract of DOI:10.1002/jccs.200200048

A simulation of the chemical transformations of methylphenanthrenes in sediment was performed using hydrous pyrolysis technique. The results indicate that isomerization is not the primary cause of the change in the MPI₁ index. Rather, the degradation reaction of methylphenanthrenes to phenanthrene is one of the most likely causes reversing the trend of the MPI₁ index with increasing the heating temperature. An unusual isomerization between 2-methylphenanthrene and 9-methylphenanthrene was also observed during the course of heating experiments. A plausible mechanism involving [1,5]-methyl shift was proposed for this isomerization reaction.

Full text of DOI:10.1002/jccs.200200048

Journal of the Chinese Chem i ca lS o ci et ,y 2002, 49, 315-317
315
Com mu ni ca tion
Hy drousPyrolysis of Methylphenanthrenes Deg ra da tio na nd
Isomerization
+
Suh-Huey Wu (
), Yane-Shih Wang (
), Lian-Xin Fan (
),
Robert, T. D. Chang (
) and Ded-Shih Huang* (
)
Department of Chemistry, Na tionalCheng Kung Uni ver s iyt , Tainan, Tai wan701, R.O.C.
A sim u la tio no f the chemical trans for ma tion os f methylphenanthrenes in sediment was per fo rmed using
hydrous py rol y si tse ch nique.The results in di cat et hat isomerization is not the primary cause of the change in
the MPI
1
in dex.Rather, the deg ra da tio nr eaction of methylphenanthrenes to phenanthrene is one of the most
index with increasing the heating tem per a ture A. n unusual
likely causes re vers ingthe trend of the MPI
1
isomerization be tween2-methylphenanthrene and 9-methylphenanthrene was also observed dur ingthe
course of heating experiments. A plausible mechanism in volv ing[1,5]-methyl shift was proposed for this
isomerization re ac tion.
Aromatic compounds are major components of oils and
or ganicex tractsof coals and sedimentary rocks. The iso-
meric distribution of various alkylated aromatic hydrocar-
bons have been widely used as ther malmaturity indicators of
1.5(3 MP
2 MP)
MPI 1
(P 9 MP 1 MP)
where P is the concentration of phenanthrene, and 3-MP,
2-MP, 9-MP and 1-MP are the concentrations of 3-, 2-, 9- and
1-methylphenanthrenes, re spec tive yl . Common to these
methyl-substituted aromatic compounds is the reduction in
the amount of the isomers in relation to the iso mers,as
1
sed i men tar yo rganic mat ter. Methylphenanthrenes have
2
-4
proven particularly at trac tivefor this pur pose. The series
of the five isomers of methylphenanthrene (MP) have been
iden ti fiedin natural ex tractsby capillary gas chromatogra-
phy coupled with mass spectrometry (GC-MS). The steric
hin dranceof 4-methyl and 5-H causes 4-methylphenanthrene
1
,7
ther malalteration in creases. Thus, an increase in the abun-
dance of 2-MP and 3-MP relative to 9-MP and 1-MP was ob-
served when the maturities were correlated with vitrinite
reflectance (Ro) in the range of 0.65 to 1.35. Unfortunately, a
6
5
7
1
reversal in the maturation trend of MPI was also ob served
4
8
3
when Ro exceeded 1.35. This un usualbehavior of MPs un der
heat stress has become a prob lemin analyzing con den sates.
Using MPI in maturity as sess men th as become a handicap as
condensates may be gen er atedfrom either immature or
over-mature source rock. To explore the mech a nismof this
CH3
2
9
1
10
(
4-MP) to be either ab sentfrom the analyte or present in
5
reversal in the mat u ra tio nt rend of MPI
of significant interest.
1
has become an area
much lower concentrations than the other four regioisomers.
Com biningthe other four isomeric MPs with phenanthrene in
1
,4
In this study, we have con ductedheating experiments
on MPs us inghydrous py rol y si ts echnique. This technique
involves main tain inga liquid water phase in contact with or-
ganic sed i men tar yr ocks or organic com poundsduring their
heating below the subcritical water tem per a tures H. ydrous
a sin gleMethylphenanthrene In dex(MPI) however, re-
sulted in a useful ma tu rit yp arameter which cor re late dc losely
6
with the vitrinite reflectance value (Ro, a measurement of
reflectance of coal macerals) of type III kerogen in the oil
4
win dow. MPI
1
is defined as fol lows:
*
+
Corresponding author. Fax: +886-6-274-0552; E-mail: dedshih@mail.ncku.edu.tw
Cur rentaddress: Exploration and Development Research Institute, Chinese Petroleum Corporation, P. O. Box 166, Miaoli, Taiwan,
R.O.C.

3
16 J. Chin. Chem. Soc., Vol. 49, No. 3, 2002
Wu et al.
pyrolysis has been demonstrated to yield oils which are most
to 1.53 with 2-MP as the dominant product. All isomerization
8
like those that occur naturally. Hydrous pyrolysis of the rock
1
reactions followed a trend similar to that of MPI , showing a
sample (Ro = 0.51) was also performed to assess the relation-
ship between heating temperature and vitrinite reflectance
decline in the amount of isomers relative to isomers, as
thermal alteration increased. The demethylation reaction also
occurred in all methylphenanthrene isomers to generate
phenanthrene under the given pyrolysis conditions. A clear
trend of increasing predominance of phenanthrene formation
with reaction temperature is evident. Clearly, the degradation
of methylphenanthrenes to phenanthrene is the cause of sole
(
Ro).
Pre-experiment on the mixtures of methylphenanthrene
isomers revealed no significant alternation of MPs during
heating at a temperature below 330 C for three days. Thus
heating experiments were performed at 330 C for three days
(
Ro = 1.07) and nine days (Ro = 1.26), and at 350 °C for three
1
influence on a reversal of the maturation of MPI when Ro ex-
days (Ro = 1.38) and nine days (Ro = 1.53). Each methyl-
phenanthrene isomer underwent hydrous pyrolysis. Table 1
shows the results. These results indicate that these methyl-
phenanthrenes were isomerized only when the maturity ex-
ceeded Ro = 1.07. However, the isomerization of 1-MP and
ceeds 1.35. Consequently, the phenanthrene concentration
should not be included as a factor in the phenanthrene matu-
ration index.
The isomerization mechanism of 2-MP and 9-MP is
also interesting and can be rationalized from the current re-
sults. Isomerization can be reasonably assumed to have pro-
ceeded by a methylation and demethylation pathway or vice
3
-MP was less significant. A remarkably high translation be-
tween 2-MP and 9-MP was observed in the Ro range of 1.26
a
Table 1. The Composition of Pyrolysates from Hydrous Pyrolysis of Individual Methylphenanthrene
b
Starting
Ro
1-MP
2-MP
3-MP
9-MP
P
C2-MP
Compound
Control
100
100
100
100
100
0
0
0
0
0
1
1
1
1
.07
.26
.38
.53
0.16
0.75
0.43
0.73
0.08
0.12
0.42
0.67
0.25
0.04
0.37
0.33
1.12
1.65
2.67
4.62
0.11
0.11
0.02
0.02
1
2
3
-MP
-MP
-MP
-MP
Control
5.48
13.78
14.51
7.80
100
100
100
100
100
0.30
1.70
1.20
0.52
0.32
0.35
1.84
38.54
10.44
9.31
0.08
1.87
5.59
4.86
15.05
0
1
1
1
1
.07
.26
.38
.53
0.53
1.86
0.22
0.07
4.58
Control
0
0
100
100
100
100
100
0
0
0
0
0.08
0.17
0.33
1
1
1
1
.07
.26
.38
.53
2.04
0.74
1.19
3.03
2.37
1.24
0.74
0.99
0.18
2.31
0.69
0.70
0.61
1.59
1.50
2.33
Control
0
0
0.01
29.70
17.41
13.30
0
100
100
100
100
100
0
0.45
1.33
6.82
11.12
0
0
0.12
0.55
0.64
1
1
1
1
.07
.26
.38
.53
0.23
1.22
0.64
0.41
0.06
0.08
0.06
0.15
9
a
Stainless steal reactors fitted with quartz cylinder tubing (Parr 4740 model) have been used in hydrous
pyrolysis study of the metylphenathrene isomers and their mixture. Typically, a 17.5 mL quartz cylinder
tubing was loaded with a 3 mg of methylphenanthrene and 8 mL of distilled water. The resulting quartz
cylinder was inserted to the reactor. The reactor was then swept with helium and pressurized to 5.5 MPa at
room temperature. The sealed reactor was placed into a high temperature oven, which was preheated to the
o
desired reaction temperature (330 or 350 C) and heated for 3 or 9 days. The resulting pyrolysates were
subjected to GC and GC-MS analysis.
b
Dimethyphenanthrene(s), the compounds were tentatively determined by comparing the mass spectra with
the standard spectra from the Wiley registry of mass spectral data.

Methylphenanthrenes Isomerization
J. Chin. Chem. Soc., Vol. 49, No. 3, 2002 317
1
1
versa since both phenanthrene and dimethylphenanthrene
were detected in the hydrous pyrolysis experiments. How-
ever, such a process could generate other isomers in approxi-
mately equal concentrations. Indeed, this mechanism could
plausibly explain the isomerization of other MP isomers.
Clearly, the intermolecular transformation of the methyl
group cannot explain the isomerization of 2-MP and 9-MP.
Many pathways involved in the intramolecular methyl
migration mechanism might be candidates. Firstly, isomer-
rearrangements of indenes and trans-15,16-dimethyldihy-
1
2
dropyrene at temperatures above 250 °C.
CH3
CH3
H
H
favorable
unfavorable
5
ization of 4-MP to 3-MP has been reported: the main driving
ACKNOWLEDGMENT
force of this rearrangement is the great steric hindrance of the
methyl group (interaction with 5-H) on the 4-MP. The details
of this [1,2]-methyl-shift-like pathway remain unclear. How-
ever, a series of such [1,2] methyl migrations involving either
The authors would like to thank the National Science
Council of the Republic of China for financially supporting
this research under Contract No. NSC 90-2113-M-006-013.
1
-MP or 3-MP as the intermediate is required to account for
isomerization between 2-MP and 9-MP. Clearly, such a
mechanism does not discriminate between isomers. Another
mechanism involved in a directly shifting methyl group from
Received February 26, 2002.
2
- to 9-position of phenanthrene ring is also less likely. Nota-
Key Words
bly, [1,5] migrations of groups other than hydrogen have been
observed only in cyclopentadienes or cyclohexadienes, in
Methylphenanthrene; Isomerization; Hydrous
pyrolysis; MPI1; [1,5]-Methyl shift.
8
which the dienes are fixed in an s-cis configuration.
Considerable evidence suggests that major hydrocar-
bons of hydrous pyrolysates are produced by a free radical
9
,10
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3
Fig. 1. A plausisble mechanism for isomerization be-
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1
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