Catagenesis and composition of petroleum: Origin of n-alkanes and isoalkanes in petroleum crudes |
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Institution: | 1. Spray Research Group, School of Computing, Science and Engineering, University of Salford, Newton Building, The Crescent, Manchester M54WT, England, UK\n;2. Department of Applied Mathematics, University of Dhaka, Dhaka 1000, Bangladesh\n;3. Renewable Energy Research, Israfil House, 243 Dickenson Rd., M13 OYW, Manchester, UK;4. Mathematics Discipline, Khulna University, Khulna 9208, Bangladesh |
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Abstract: | Distribution of n-alkanes and isoalkanes in ca. 50 petroleum crudes have been examined by the gas chromatography. Molar distributions of n-alkanes with respect to their c atom numbers in the majority of crudes follow the exponential law, which signifies a random, chemical nature of n-alkane-generating processes occurring in the catagenesis stage of petroleum maturation. Similar distributions of n-alkanes were found in the products of mild thermolysis of heavy n-alkanes.Isoalkanes represent a major, 10–25%, petroleum component. The principal types of isoalkanes in crudes are monomethyl-branched, with the branches randomly positioned in the chains, and dimethyl-branched with one of the methyl groups predominantly in the second position in the chains. Thermolysis studies of individual n-alkanes, alkanoic acids, and esters in the presence of various minerals provided an explanation of the n-alkane and isoalkane distributions. Selected heavy n-alkanes are initially formed in decarboxylation reactions of heavy n-alkanoic acids and esters. Extensive thermocracking produces mixtures of lighter n-alkane and α-olefins. The olefins, in the presence of acidic clays, are converted in cationic reactions into mixtures of predominantly mono- and dimethyl-branched isoalkanes. |
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