Origin of long-chain alkylcyclohexanes and alkylbenzenes in a coal-bed wax
- Brigham Young Univ., Provo, UT (United States)
A coal-bed wax was fractionated and analyzed using capillary column GC and combined GC/MS. It was found that the major components in the wax were n-alkanes (55.6%), cyclic/branched alkanes (26.0%) and several homologous series of alkylbenzenes (5.7%). All alkybenzene isomers (Except 6-n-alky-m-xylene) were positively identified by comparison with the retention times and mass spectra of newly synthesized authentic standards. 5-n-Alkyl-m-xylene, 2-n-alkyl-p-xylene, 4-n-alkyl-m-xylene, 4-n-alkyl-o-xylene, 2-n-alkyl-m-xylene, and 3-n-alkyl-o-xylene were identified for the first time from geological sources. All of these long-chain alkyl compounds (e.g., n-alkylcyclohexanes, n-alkylbenzenes, n-alkyl-o-toluenes, n-alkyl-p-toluenes, and 5-n-alkyl-m-xylenes) have similar total carbon number distributions and maxima with a slight even over add carbon number preference between C[sub 28]-C[sub 30]. Moreover, the carbon number distributions of these compounds resembled those of the n-alkanes found in the same wax with slight odd over even carbon preference between C[sub 27]-C[sub 31]. This indicates that the alkylcyclohexanes and alkylbenzenes may have the same fatty acid precursors as the n-alkanes. The alkylcyclohexanes and alkylbenzenes could have been formed by direct cyclization and aromatization, while the n-alkanes could have been formed by decarboxylation of the straight chain fatty acids. This explanation is further supported by the identification of homologous series of tetramethyl-n-alkylbenzenes and pentamethyl-n-alkylbenzenes with relatively high abunances at C[sub 15], C[sub 16], and C[sub 18], and a fatty acid distribution with maxima at C[sub 16] and C[sub 18]. Based on these findings, mechanisms for the conversion of fatty acids or alcohols to alkylcyclohexanes and alkylbenzenes are proposed.
- OSTI ID:
- 6938516
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:4; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
ALCOHOLS
ALKANES
AROMATICS
AROMATIZATION
BENZENE
CALIBRATION STANDARDS
CARBON
CARBONACEOUS MATERIALS
CARBOXYLIC ACIDS
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
COAL
CONVERSION
CYCLIZATION
CYCLOALKANES
CYCLOHEXANE
DECARBOXYLATION
DISTRIBUTION
ELEMENTS
ENERGY SOURCES
FOSSIL FUELS
FUELS
HYDROCARBONS
HYDROXY COMPOUNDS
ISOMERS
MASS SPECTRA
MATERIALS
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORIGIN
OTHER ORGANIC COMPOUNDS
QUALITATIVE CHEMICAL ANALYSIS
QUANTITATIVE CHEMICAL ANALYSIS
SPECTRA
STANDARDS
SYNTHESIS
WAXES