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 kinetic model based on mass balances 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.

Funding category: Financement public/privé
IFPEN
PHD title: Doctorat de Génie Chimique
PHD Country: France