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In general, aromatic hydrocarbons have a tendency of increasing
in the β-type to the α-type isomer ratio with increasing in
thermal maturity.Although, the β/α ratio in methylphenanthrene
isomers do increase with increasing in low thermal maturity
sediments, this ratio was found decreasing in higher thermal
maturity level. Radke et al. Claimed the drastic decrease in β/
α ratio is due to the organic facies. However, such a phenomena
could be also possibly caused by the differences in the thermal
stability of thylphenanthrenes. In order to examine the relative
thermal stability of methylphenanthrene isomers the current
studies was conducted. Five methylphenanthrenes were prepared
and suggested to Lewan type hydrous pyrolysis experiment.
The results from hydrous pyrolysis studies indicated that
phenanthrene can be generated from all the methylphenanthrene
isomers. In addition, part of isomers can be exchanged during
the examining condition. Thus, 2-MP could be isomerized to 9-MP,
both 1-MP and 9-MP could be generated from 3-MP, and 2-MP also
can be generated from 9-MP. When a mixture with nearly equal
amount of 1-, 2-, 3- and 9-MP was suggested to hydrous pyrolyze
in 330℃and 350.℃, the β/α ratio was found decreased in 330℃
and further deeased in 350℃. These results suggest that the
decreasing in β/α ratio is due to the different in the thermal
stability of methylphenanthrene isomers.
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