PET recycling: Influence of impurities on the crystallization of BHET monomer

Recycling of PET polymer through chemical recycling routes has attracted a great deal of interest in recent years, to cope with plastics streams not handled by classical industrial PET mechanical recycling routes. The development of recycling processes dedicated to colored and opaque PET is a major challenge for reducing waste, developing new resources for the production of recycled PET, and therefore reducing the use of fossil resources to produce PET.
PET depolymerization based on glycolysis leads to the production of the monomer BHET, for bis(2-hydroxyethyl) terephthalate. However, monomer purification, which aims at removing comonomers and colorants, is an important challenge. Solution crystallization, which takes benefit from the solubility difference in a given solvent, shows promising results toward this matter. Working with recycled feedstocks differentiates from conventional process since there are numerous and unknown impurities as well as an important variability between feedstocks (as packaging, textiles…). However, presence of impurities greatly affects crystallization process operation, by modifying the nucleation and growth kinetics as well as the solubility.
This PhD thesis will focus on understanding and modeling the effect of impurities on the crystallization of BHET obtained from recycled PET, and on the evolution of crystal size distribution. The study will include an experimentation part, where process analytical tools for in-line measurement of solvent composition, and of crystal size and shape will have to be implemented at lab scale on an existing crystallization equipment. This will be used to investigate the influence of impurities on BHET solubility and crystallization kinetics. It will be associated to a modeling work that will provide insight on crystals growth kinetics and nucleation rate.
Development of recycling solutions for plastic materials is a major environmental challenge. This PhD position is an opportunity to contribute to it.

Keyword: Circular Economy, Plastic Recycling, Chemical Engineering, Crystallization, Experiment, Modeling

• Academic supervisor    Dr. PUEL François, Chemical Engineering and Materials Research Department (LGPM) at CentraleSupélec - Paris-Saclay University,  https://cv.archives-ouvertes.fr/francoispuel
• Doctoral School    ED 579 SMEMaG, Paris-Saclay University
• IFPEN supervisor    BLANCKE Guillaume, Chemical Engineering & Technology Department, guillaume.blancke@ifpen.fr
• PhD location    IFP Energies nouvelles, Lyon, France 
• Duration and start date    3 years, starting in November 2022
• Employer    IFP Energies nouvelles, Lyon, France 
• Academic requirements    University Master degree in Chemical Engineering or Chemical Sciences
• Language requirements    Fluency in English, willingness to learn French
• Other requirements    Programming skills (Matlab, Python, …) preferred