Modeling and simulation of twin-screw extrusion with solvent injection for plastic waste recycling

Plastic wastes recycling is a major environmental issue. Although European regulations are initiating major changes in terms of collection and incorporation of recycled materials, technologies for recycling such complex streams still must be developed. This problem is particularly true when the recyclates are intended for food use: meeting purity standards of the virgin materials is most often mandatory. The use of solvents to dissolve or depolymerize these materials is well suited because it allows an easier elimination of impurities.
For this purpose, twin-screw extruders with solvent injection are a promising technological solution since it offers plastic material melting and mixing with a solvent in the same equipment. However, the injection of large quantities of solvent presents difficulties and is poorly documented in the literature. If the development on laboratory tools is feasible, classical extrapolation rules do not apply anymore because of the modified heat transfers due to the presence of the solvent and to the viscosity drop.
The present PhD proposes to use CFD to better understand and design this type of equipment. The stationary and transient approaches, without addition of solvent, will be successively evaluated, with the increasing degree of difficulty of meshing that they imply. Then, solvent/polymer mixing laws as well as heat transfer will be implemented in the numerical models, and eventually a depolymerization kinetic. Trials on a laboratory scale extruder and with different types of polymer/solvent systems will provide useful data to compare with numerical results. Finally, application to larger a larger extruder scale will allow to validate the extrapolation ability of the developed models.

Keywords: Fluid mechanics, CFD, Reactive extrusion, Polymers, Plastic Waste Recycling

• Academic supervisor    Pr. FULCHIRON René, Laboratoire Ingénierie des Matériaux Polymères, ORCID - 0000-0002-7714-9298
• Doctoral School    ED34, Ecole Doctorale Matériaux (Lyon 1), https://ed34.universite-lyon.fr/
• IFPEN supervisor    Dr GAMET Lionel, R&D Engineer, Experimentation Intensification Department, ORCID - 0000-0002-8280-1359 
• PhD location    IFP Energies nouvelles, Lyon, France
• Duration and start date    3 years, starting in the fourth quarter 2025 (Novembre 3)
• Employer    IFP Energies nouvelles, Lyon, France
• Academic requirements    University master’s degree in CFD/Fluid Mechanics and/or Polymer Science
• Language requirements    Fluency in French or English, willingness to learn French
• Other requirements    Highly recommended: CFD, OpenFOAM, C++, rheology

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