“…There is also an increasing overall abundance of shorter chain length n -alkanes with increasing thermal maturity, which is similar to trends observed for other coals and is interpreted as reflecting the progressive generation of n -alkanes . The bimodal C 9 - 34 n -alkane compositional profiles shown in parts C and D of Figure replicate ones observed in chromatograms of oils derived from coaly organic matter sources 7-10 or obtained by closed-system pyrolysis of coal. , This bimodal carbon number profile also mimics the compositional trait profiles exhibited by the biogenic n -alkanoic acids extracted from brown coals (see Figure ). , 3 Histograms of n -alkane carbon chain length predominance in supercritical CO 2 extracts of selected coals: (A) Beulah-Zap, CPI = 2.70; (B) Wyodak-Anderson, CPI = 2.44; (C) Blind Canyon, CPI = 1.56; (D) Intermediate Fruitland, CPI = 1.22. 4 Histogram of n -alkanoic acid carbon chain length predominance in Yallourn brown coal (data from ref ).…”
Section: Resultssupporting
confidence: 78%
“…23,25 This bimodal carbon number profile also mimics the compositional trait profiles exhibited by the biogenic n-alkanoic acids extracted from brown coals (see Figure 4). 28,29 A simple carbon-number correspondence exists between the C 9+ n-alkanes present in the supercritical CO 2 extracts and the n-alkanoic acids present in brown coals except for a one carbon-number shift. The dominant…”
Section: Resultsmentioning
confidence: 99%
“…Histogram of n -alkanoic acid carbon chain length predominance in Yallourn brown coal (data from ref ).…”
The compositional traits of C 9-34 n-alkanes were measured in supercritical CO 2 extracts from 14 U.S. coals of varied geologic ages and wide thermal maturity range (lignite through lowvolatile bituminous). The analysis data exhibit no unique component depletion pattern signatures diagnostic of known types of postgeneration physical, chemical, or microbiological degradation processes that commonly affect crude oil in sedimentary rocks. The C 9-34 n-alkanes in Paleocene and Upper Cretaceous age coals exhibit bimodal carbon-number distribution profiles that strongly resemble those of the biogenic n-alkanoic acids present in brown coals. The compositional trait similarities between these n-alkanes and n-alkanoic acids and the covariance of the bulk coal organic matter atomic oxygen-to-carbon (O/C) ratios and carbon-preference index (CPI) values offer tangible evidence for the existence of a genetic linkage between these two series of compounds. Our analysis results indicate that the C 2-5 alkanes and C 6+ hydrocarbons in coals attain their maximum abundances over the thermal maturity interval from 0.50 to 0.72% R 0 , which, in turn, strongly suggests that these two groups of compounds are formed concurrently by similar overall reaction processes during coal maturation. The compositional traits of the C 4-5 alkanes and C 9-34 n-alkanes in coals appear to uniquely mimic those of the alkane products formed by mineral-catalyzed defunctionalization and cracking of n-alkanoic acids, which suggests that mineral catalysis rather than temperature-controlled thermolysis may be a critical variable controlling the formation and compositional traits of natural gas and C 9+ n-alkanes during coal maturation. These mechanistic insights should be useful to those seeking to formulate improved geochemical models for predicting hydrocarbon evolution during coal maturation.
“…There is also an increasing overall abundance of shorter chain length n -alkanes with increasing thermal maturity, which is similar to trends observed for other coals and is interpreted as reflecting the progressive generation of n -alkanes . The bimodal C 9 - 34 n -alkane compositional profiles shown in parts C and D of Figure replicate ones observed in chromatograms of oils derived from coaly organic matter sources 7-10 or obtained by closed-system pyrolysis of coal. , This bimodal carbon number profile also mimics the compositional trait profiles exhibited by the biogenic n -alkanoic acids extracted from brown coals (see Figure ). , 3 Histograms of n -alkane carbon chain length predominance in supercritical CO 2 extracts of selected coals: (A) Beulah-Zap, CPI = 2.70; (B) Wyodak-Anderson, CPI = 2.44; (C) Blind Canyon, CPI = 1.56; (D) Intermediate Fruitland, CPI = 1.22. 4 Histogram of n -alkanoic acid carbon chain length predominance in Yallourn brown coal (data from ref ).…”
Section: Resultssupporting
confidence: 78%
“…23,25 This bimodal carbon number profile also mimics the compositional trait profiles exhibited by the biogenic n-alkanoic acids extracted from brown coals (see Figure 4). 28,29 A simple carbon-number correspondence exists between the C 9+ n-alkanes present in the supercritical CO 2 extracts and the n-alkanoic acids present in brown coals except for a one carbon-number shift. The dominant…”
Section: Resultsmentioning
confidence: 99%
“…Histogram of n -alkanoic acid carbon chain length predominance in Yallourn brown coal (data from ref ).…”
The compositional traits of C 9-34 n-alkanes were measured in supercritical CO 2 extracts from 14 U.S. coals of varied geologic ages and wide thermal maturity range (lignite through lowvolatile bituminous). The analysis data exhibit no unique component depletion pattern signatures diagnostic of known types of postgeneration physical, chemical, or microbiological degradation processes that commonly affect crude oil in sedimentary rocks. The C 9-34 n-alkanes in Paleocene and Upper Cretaceous age coals exhibit bimodal carbon-number distribution profiles that strongly resemble those of the biogenic n-alkanoic acids present in brown coals. The compositional trait similarities between these n-alkanes and n-alkanoic acids and the covariance of the bulk coal organic matter atomic oxygen-to-carbon (O/C) ratios and carbon-preference index (CPI) values offer tangible evidence for the existence of a genetic linkage between these two series of compounds. Our analysis results indicate that the C 2-5 alkanes and C 6+ hydrocarbons in coals attain their maximum abundances over the thermal maturity interval from 0.50 to 0.72% R 0 , which, in turn, strongly suggests that these two groups of compounds are formed concurrently by similar overall reaction processes during coal maturation. The compositional traits of the C 4-5 alkanes and C 9-34 n-alkanes in coals appear to uniquely mimic those of the alkane products formed by mineral-catalyzed defunctionalization and cracking of n-alkanoic acids, which suggests that mineral catalysis rather than temperature-controlled thermolysis may be a critical variable controlling the formation and compositional traits of natural gas and C 9+ n-alkanes during coal maturation. These mechanistic insights should be useful to those seeking to formulate improved geochemical models for predicting hydrocarbon evolution during coal maturation.
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