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Journal Articles Journal of Analytical and Applied Pyrolysis Year : 2016

Pyrolysis of n- octane at very low concentration and low temperature

Abstract

tHydrocarbon pyrolysis concerns many different fields (petroleum geochemistry, refinery, fuel thermalstability, pyrocarbon deposition, etc.). It is therefore studied in a wide variety of temperature–pressureexperimental conditions, which strongly affect the chemistry of hydrocarbons cracking.An experimental study of the pyrolysis of n-octane has been performed at very low reactant concen-tration (1 mbar diluted in inert gas − total pressure 1500 mbar − molar fraction 0.07%) in a closed reactor,at temperatures ranging between 350◦C and 450◦C, and reaction time from 1 h to 70 h. The major prod-ucts of the reaction are 1-alkenes (C2H4to C7H14), methane and ethane; other alkanes (C3H8to C6H14)are minor products. At 450◦C and 4 h, the conversion is close to 9% and we observe, in terms of molarfractions:C2H4> C3H6≈ CH4> C4H8> C5H10> C6H12≈ C2H6> C7H14These experimental results are very different from those of the thermal decomposition of n-alkanesat the same low temperature but at high pressure. In particular, the cracking stoichiometric equations(for example: C8H18= C6H14+ C2H4) are not observed since alkanes (except methane and ethane) are invery low quantities. This can be explained by the very low concentration of reactant which limits thebimolecular reactions. In our conditions, the radicals decompose several times by beta-scissions of CCbonds when it is possible (unimolecular reaction), rather than react by H-transfers (metathesis) with thereactant (bimolecular reaction) which produce alkanes. A detailed free radical mechanism (184 reactions,16 molecules and 18 radicals— mechanism available as Supplementary material) allows modeling theexperimental results.
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Dates and versions

hal-02930918 , version 1 (03-02-2022)

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Attribution - NonCommercial - NoDerivatives

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N. Razafinarivo, R. Bounaceur, V. Burklé-Vitzthum, F. Lannuzel, R. Michels, et al.. Pyrolysis of n- octane at very low concentration and low temperature. Journal of Analytical and Applied Pyrolysis, 2016, 117, pp.282-289. ⟨10.1016/j.jaap.2015.11.004⟩. ⟨hal-02930918⟩
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