Towards the chemical recycling of plastic wastes: Understanding plastic pyrolysis oil hydrodechlorination

In the context of growing interest in circular economy solutions, chemical recycling by pyrolysis is a promising way of converting plastic and tyre waste into pyrolysis oil and then back into monomers and/or chemical bases in steam cracking or refining processes.
However, the presence of chlorine in pyrolysis oils poses major problems for downstream recovery processes: deactivation of catalysts, fouling and corrosion. Dechlorination by hydrotreatment of pyrolysis oils is therefore a necessary purification step upstream of recovery processes.
Due to the presence of various contaminants (nitrogen, sulphur, oxygen) and cracking products (olefins, diolefins) in pyrolysis oils, dechlorination reactions are strongly affected by matrix effects, involving, for example, competitive adsorption between reactants as well as recombination of HCl with olefins or nitrogen compounds. Understanding these phenomena is essential for the design of innovative catalyst formulations and dedicated process schemes, as well as for the kinetic modelling of hydrodechlorination reactions in pyrolysis oils.
The aim of this thesis will therefore be to further our understanding of hydrodechlorination reaction kinetics and the associated matrix effects. To this end, the thesis will comprise two parts focusing on experimentation and kinetic modeling of the test data obtained. The experiments will be carried out on a continuous flow pilot-scale reactor at IFPEN to study the reactivity, kinetics, and effects of operating conditions on various reactions. The experiments will be carried out with several model molecules (organochlorine, olefin, and nitrogen compounds), and finally on a real feedstock of pyrolysis oil from plastics. Advanced analytical techniques will be used to characterize the feedstocks and effluents. Finally, a numerical and mathematical model will be used to study the kinetics and matrix effects between the molecules, and then to apply the knowledge obtained to the hydrotreatment of real feedstocks.

Keywords: Circular economy, pyrolysis oil, chlorine removal, catalysis, kinetic, chemical engineering

• Academic supervisors   Prof. Melaz TAYAKOUT, LAGEPP, Université Lyon 1 & Dr. Gerhard PIRNGRUBER, IFPEN, ORCID: 0000-0003-0688-425X
• Doctoral School    ED206, Ecole Doctorale de Chimie de Lyon, Université Lyon 1
• IFPEN supervisor    Dr. Minh Tuan NGUYEN, ORCID: 0000-0003-1284-9354
• PhD location    IFPEN, Solaize, France 
• Duration and start date    3 years, starting in the fourth quarter 2024 (Novembre 4)
• Employer    IFPEN
• Academic requirements    University Master’s Degree in Chemical Engineering / Chemistry
• Language requirements    English level B2 (CEFR), willing to learn French
• Other requirements    Knowledge in kinetics with aptitude and interest in heterogeneous catalysis. Knowledge in mathematical modeling is a plus.

To apply, please send your cover letter and CV to the IFPEN supervisor indicated below.