Highly oxygenates molecules formed by oxidation of terpenes in a jet-stirred reactor

Abstract : With the growing interest for biomass-derived fuels the understanding of the combustion chemistry of terpenes becomes of major scientific importance. Terpenes have been proposed as biofuels for aviation because of their high energy density. They usually develop cool flames below 800 K. Very complex processes occur there, with the formation of peroxides intermediates such as ketohydroperoxides and highly oxidized molecules (HOMs) containing both hydroperoxy and carbonyl groups. Such chemicals are relatively unstable and difficult to analyze. We studied the low-temperature oxidation of alpha-pinene, beta-pinene, and limonene (C10H16) in a jet-stirred reactor. The experimental conditions were selected to maximize the production of ketohydroperoxides. We oxidized 5000 ppm of these three terpenes at 1 bar, T = 590 K, an equivalence ratio of 0.5, and at a residence time of 1 s. High-resolution mass spectrometry analyses were performed on solubilized products of terpenes oxidation in cooled acetonitrile. The samples were analyzed using soft HESI electrospray ionization (+/-) and an Orbitrap® mass spectrometer (resolution: 140,000, mass accuracy <0.5 ppm RMS). The formation of ketohydroperoxides and highly oxygenated compounds resulting from third O2 addition on the fuels primary radical (R) was observed: R + O2 <=> RO2 <=> QOOH; QOOH + O2 <=> OOQOOH <=> HOOQ’OOH followed by HOOQ’OOH + O2 <=> (HOO)2Q’OO <=> (i) (HOO)2POOH → OH + (HOO)2P=O (i.e., C10H14O5) and (ii) (HOO)2POOH + O2 → (HOO)3POO <=> (HOO)3P’OOH → OH + (HOO)3P=O (i.e., C10H14O7). Fourth oxygen addition yielding C10H14O9 was also observed in the present work. Hydrogen–Deuterium exchange reactions using D2O were used to confirm the presence of –OH groups in the products.
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Submitted on : Thursday, May 23, 2019 - 9:19:24 AM
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N. Belhadj, R. Benoit, P. Dagaut, G. Dayma, M Lailliau, et al.. Highly oxygenates molecules formed by oxidation of terpenes in a jet-stirred reactor. 11th International Conference on Chemical Kinetics, Jun 2019, Orléans, France. ⟨https://icck2019.sciencesconf.org/⟩. ⟨hal-02137425⟩

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