Thesis at PC2A depends on the doctoral (ED 104) SMRE Science de la Matière, du Rayonnement et de l'Environnement of the University of Lille.
This proposal is filled
Selenium (Se) is an essential dietary nutrient. Its biogeochemical cycle, including its atmospheric component, influences animal and human health through biological processes that regulate our daily lives, like the immune system and thyroid function. The recommended dietary intake range of Se is narrow, with safe daily intake levels between 20 to 450 μg for adults. Humans and animals obtain Se from their diet, wherein the Se content of plant-based foods depends on the amount of bioavailable Se in agricultural soils. Atmospheric deposition is a major source of Se to
agricultural soils, and atmospheric cycling of Se is a potential driver for soil Se distribution.
Atmospheric Se is thought to have four main sources: anthropogenic, marine biosphere, terrestrial biosphere, and volcanic emissions. Reduction with subsequent methylation by microorganisms of inorganic Se play an important role in the formation of volatile Se species, such as methane selenol, dimethyl selenide or dimethyl diselenide found in marine systems. Volatilization can lead to gas-phase emission of such organo-selenides from the aquatic phase. It is generally postulated that organic Se compounds have a rather short lifetime in the atmosphere, where they are being rapidly oxidized and consequently partition to the particle phase. However, the available information is preventing us from predicting the chemical speciation and the fate of volatile organic Se compounds in the atmosphere. With changing climates, there is an urgent need to model Se’s biogeochemical cycle in order to mitigate future Se deficiencies.
In addition to the experiments that will be performed at the University of British Columbia, this thesis project will evaluate the fate of Se-containing species by using computational chemistry tools to
elucidate the stepwise chemical oxidation mechanism of atmospheric Se to enable the predictive capabilities of the fate of these compounds for future Se-soil distribution maps. Ultimately, this project will provide insight into currently unknown aspects of gas phase oxidation of selenium leading to an improved modeling of the fate of Se and its impact on soil distribution in a changing climate.
In recent decades, theoretical kinetics has contributed significantly to a better understanding of a significant number of atmospheric reactions and has made it possible to estimate the associated rate constants with chemical accuracy. This improvement has been the result of important advances in computational tools and the precision of theoretical methods (i.e., theories of electronic structure and chemical kinetics). A systematic benchmark study of the suitable theoretical methods will be performed for assessing different properties such as for example geometrical parameters, vibrational frequencies, and bond strengths for selenium-containing species. In a second step, this project aims to shed some light in the understanding of the experimental facts and to determine both thermochemical properties and kinetics parameters for the commonly studied molecular systems. The goal is to inform the experiments on recommended products to look for, and vice-versa, to
support the kinetics and products already identified. The use of theoretical kinetics will also be helpful to determine all reaction channels whenever the products could not be identified in the
experiments. These results will provide new knowledge on the fate of Se compounds in the atmosphere in order to assess their atmospheric transport, their fate, and ultimately their spatial distribution to
assess future Se deficiencies.
Supervisors: Florent Louis and Nadine Borduas-Dedekind (Université de Colombie Britannique, Vancouver, Canada)
Financial support: thèse labellisée Université de Lille (graduate program) et Labex CaPPA (acquis)
The transformations of atmospheric pollutants emitted by human activities and present in the atmosphere and in indoor environments is a key question because of their impact on health, environment and climate change.
Indeed, numerous gaseous pollutants, mainly volatil organic compounds (VOC) are oxides by radiclas (highly reactive chemical species) such as OH (hydroxyl radical). This process generates more oxidised compounds, potentially more hazardous that the primary emitted species and heavier compounds leading to secondary organic aerosols (SOA).
This cycle is also responsible, in presence of nitric oxide (NO, from combustion processes), of the tropospheric ozone formation having a negative impact on health, plants and which is a Green House Gas (GHG).
In low NO environments, the oxidation processes are less known because radical-radical reactions are involved and are complex to study.
The work proposed in this thesis is based on an experimental approach of the oxidation processes using a characterisation technique of atmospheric radicals OHand HO2, both involved on these processes. The chemical reactivity of target species identified thanks to the European COST action INDAIRPOLLNET will be studied by the FAGE technique (Fluorescence Assay by Gas Expansion). This technique based on laser diagnostic is selective and sensitive and only used by about 10 laboratories in the World.
Expected date of recruitment : 01/10/2023
Contact (e-mail address) : firstname.lastname@example.org
Additional remarks/comments: application ADEME to submit, candidat for the PhD should be identify for the application, deadline end of March. If interested please contact us ASAP
This proposal is filled
This PhD thesis is part of the ambitious program “Support innovation to develop new largely carbon-free industrial processes” supported by the French Government in the framework of the decarbonization of the industry to achieve carbon neutrality by 2050.
The decarbonation of the industry partly relies on the development and intensification of processes for CO2 capture. This PhD thesis is offered as part of the OXY3C project aiming at improving knowledge and skills in oxycombustion for the optimization of eco-efficient processes. The consortium working on this project gathers seven French academic laboratories and IFPEN.
Objectives of the thesis:
This study aims at investigating chemical kinetics of soot precursors and measuring soot particles from biomass’s tar surrogates in the framework of a close collaboration between PC2A, LRGP, and IFPEN. Experiments and simulations will be performed under CO2 and H2O vapor atmosphere at a wide range of temperatures covering the temperature range in the Chemical Looping Combustion application. This work comprises two main parts.
The first part is establishing a reliable experimental database that includes mole/volume fraction profiles of reactants, products, intermediates and soot particles in the pyrolysis and combustion of a biomass’s tar surrogate. These data will be measured in a burner system at PC2A and in a jet-stirred reactor or a tubular reactor at LRGP. Chemical species will be measured using gas chromatography and mass spectrometry. Soot volume fraction profiles in flames will be measured in situ by extinction or cavity ring-down extinction. Selected soot samples thermophoretically collected in the above flames will be analyzed at IFPEN for characterizing soot morphology using microscopy (STEM + possibly TEM or HRTEM).
The second part is developing a detailed kinetic model for soot precursor formation from the pyrolysis and combustion of this biomass’s tar surrogate. The model will include a base model containing common species, a sub-model for the pyrolysis and combustion of a biomass’s tar surrogate, a sub-model of aromatics. The model will be tested against the experimental database under CO2 and H2O atmosphere that will be obtained in the above experimental part. The model will be transferred to IFPEN for soot modeling.
Candidates must have a master degree, in chemistry-physics or process engineering. Modeling and experimental skills, experiences in the field of combustion and chemical kinetics will be appreciated. Fluent English and ability to work in a team are expected.
Dr. Luc-Sy TRAN, CNRS Research Scientist at PC2A UMR 8522, CNRS, University of Lille, luc-sy.tran()univ-lille.fr, https://pro.univ-lille.fr/luc-sy-tran/
Dr. Pascale DESGROUX, CNRS Research Director at PC2A UMR 8522, CNRS, University of Lille, pascale.desgroux()univ-lille.fr
Remuneration: ~2100 € gross income per month
Duration and start date of the thesis: 3 years with a start in October 2023 after recruitment
Practical information: The thesis will take place mainly at PC2A (https://pc2a.univ-lille.fr/) in Lille, France. A stay of 6 months at LRGP (https://lrgp-nancy.cnrs.fr/) in Nancy, France is planned.
How to apply: Email to the scientific leaders mentioned above:
- your CV
- a cover letter