Position-specific distribution of hydrogen isotopes in natural propane: Effects of thermal cracking, equilibration and biodegradation

Abstract

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Predicting isotopologue abundances in the products of organic catagenesis with a kinetic Monte-Carlo model

“…Our results demonstrate that scheme B also better mimics lab experiments in origins of alkane hydrogen. However, we note that wateralkane hydrogen isotope exchange is suggested to play an important role in higher maturity catagenesis (Sessions et al, 2004;Xie et al, 2020;Xie et al, 2021).…”

“…It is also possible that some of the heterogeneity in isotopic compositions of biomolecules does not lead to systematic position-specific isotopic variations in kerogens or oil compounds simply because the latter are statistically averaged across many precursors sampled through many intermediate reactions. For example, the previous model of Xie et al (2020) shows that differences in δ 13 C between odd and even carbon sites in n-C17 alkane precursors have little impact on position-specific isotope values of propane formed by thermal cracking (Xie et al, 2020). Yet we acknowledge that this problem is understudied and encourage future research to provide better constraints on internal isotope distributions in kerogen (e.g., see Keppler et al, 2004Keppler et al, , 2007Lloyd et al, 2021 for studies of 13 C and D distribution in lignin).…”

“…Finally, our model considers both 13 C and D substitution and provides abundances of site-specific and multiply-substituted isotopologues for C 1 -C 7 product molecules. Note that Xie et al (2020) present a preliminary and simplified version of this model to calculate position-specific hydrogen isotope ratios of propane produced by catagenesis of kerogen and oil compounds.…”

“…It has been previously demonstrated that the intramolecular isotopic fractionation of the products of hydrocarbon cracking is largely controlled by precursor chemical structure (Xie et al, 2020). The rationale is that isotopic depletion on certain sites of products is usually associated with expression of KIE's of bond dissociation reactions.…”

Clumped isotope effects of thermogenic methane formation: Insights from pyrolysis of hydrocarbons

“…The relatively rapid rise in δD and Δ 12 CH 2 D 2 of methane in our experiments could reflect several processes, but we focus our attention on hydrogen exchange because it is known to be an important process both in pyrolysis experiments and in nature (Sessions et al, 2004;Schimmelmann et al, 2006;Sessions, 2016;Wei et al, 2019;Labidi et al, 2020;Xie et al, 2020).…”