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Kinetic mechanisms of low temperature oxidation of unsaturated hydrocarbons and biofuels. Determination of intermediates by (1) time-of-flight mass spectrometry and photoionization by synchrotron radiation and by (2) Orbitrap-UHPLC-APCI-HESI-APPI.
Current liquid fuels come from petroleum and their partial replacement by renewable products derived from biomass or agriculture is planned in all industrialized countries. The goals are to reduce dependence on oil, whose reserves are dwindling, and to limit emissions of carbon dioxide (greenhouse gas). Adapting current engines and hybrid engines to these new fuels (first and second generation) requires in-depth knowledge (a) of their combustion and self-ignition kinetics and (b) of the nature and concentrations of pollutants emitted during their use.
The project aims at a better understanding of the kinetic processes of combustion of 'bio-fuels' and of isolated constituents and at the identification of the 'specific' pollutants resulting from the combustion of ‘new fuels’ by combining complementary techniques and modeling. We will focus on determining the relative importance of the mechanisms of Korcek (formation of ketones and carboxylic acids by decomposition of γ-ketohydroperoxides), Waddington (successive addition of OH and O2 on olefins then decomposition and formation of carbonyl compounds and OH) and “roaming radicals” (formation by rearrangement of stable compounds from radicals). The formation of HOMs (Highly Oxygenated Molecules) via "unconventional" hydrogen transfers will be studied. These compounds which are generally neglected in combustion models are very important in tropospheric chemistry where they can lead to the formation of particles.
The thesis will be divided into two parts: (1) an experimental study and (2) a kinetic modeling.
1-Experimental study
A study of the oxidation kinetics of constituents of future 2nd generation biofuels and mixtures will be performed. This experimental study will use:
(1) In ICARE at Orleans, a self-stirred gas jet reactor (JSR) capable of operating in a wide range of temperatures (300-1400K), pressures (1-10 atm), equivalence ratios (0.1-4) and residence time (40 ms-2s). The reagents, products and intermediates will be measured by analyzing samples by infrared absorption (FTIR), GC-MS, UHPLC-Orbitrap MS (APCI, HESI, APPI).
(2) A second JSR, located in a Synchrotron lab., that can operate over similar conditions is coupled to a high-resolution time-of-flight mass spectrometer using photoionization by synchrotron. Reagents, products, and intermediates (including radicals) will be measured.
The experimental study, implementing complementary techniques, will allow building a database on the combustion/autoxidation of the selected fuels for the validation of a detailed kinetic mechanism.
2-Kinetic modeling
The experimental results obtained in a homogeneous reactor will be used to propose and validate a detailed kinetic model for fuel combustion/autoxidation. This work will be based on models previously developed in the laboratory for the combustion of hydrocarbons, oxygenates, commercial fuels. This project will contribute to improving our knowledge of the kinetic mechanisms of autoxidation / combustion, to the protection of the environment since the fuels concerned must contribute to reducing both pollutants and fossil carbon dioxide emissions. The PhD student will get in-depth fundamental knowledge of cutting-edge techniques and kinetic modeling, and the opportunity to experience international collaborations.
Location: Orléans, Laboratory ICARE, France
Net Salary: 1420€ / month, opportunity for 1660€/month with extra missions (e.g. teaching)
Keywords: biofuels, combustion, autoxidation, pollutants, highly oxygenated molecules, jet-stirred reactor, Orbitrap, mass spectrometry, chromatography, synchrotron,
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To apply, send an e-mail with CV and motivation letter to Dr. Philippe DAGAUT (PhD advisor):
philippe.dagaut@cnrs-orleans.fr
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