Valorisation hydrothermale du polyéthylène téréphtalate (PET) par liquéfaction et carbonisation : optimisation des conditions opératoires

Abstract

In the context of the global plastic pollution crisis, this thesis presents an integrated experimental approach for the valorization of polyethylene terephthalate (PET) via hydrothermal conversion, combining two complementary thermochemical pathways: hydrothermal liquefaction (HTL) and hydrothermal carbonization (HTC). The dual objective is to (i) induce controlled depolymerization of the polymer to recover valuable monomeric compounds and (ii) generate a carbonaceous residue suitable for energy recovery or functional applications. HTL was carried out at 200 °C for 5 hours in an alkaline medium (1 M NaOH), with a PETto- water ratio of 1:15, using a hot plate. High-performance liquid chromatography (HPLC) analysis of the liquid phase confirmed the formation of terephthalic acid (TPA), bis(2- hydroxyethyl) terephthalate (BHET), and mono(2-hydroxyethyl) terephthalate (MHET), indicating partial cleavage of the ester bonds. HTC was performed in a hermetically sealed Teflon reactor under microwave irradiation (1,200 W) at 200 °C for 16 minutes. The resulting solid residue (hydrochar) was characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and bomb calorimetry. The results demonstrate that hydrothermal liquefaction (HTL) promotes the recovery of compounds such as terephthalic acid (TPA), bis(2-hydroxyethyl) terephthalate (BHET), and mono(2-hydroxyethyl) terephthalate (MHET), while hydrothermal carbonization (HTC) produces a porous, thermally stable, and high-energy-density carbonaceous material. The assessment of energy consumption further confirms the efficiency of microwave heating. These findings highlight the potential of hydrothermal conversion of PET for the simultaneous production of reusable chemical intermediates and valuable carbon residues, paving the way for process optimization and a more sustainable approach to plastic management.

Date	7 Oct 2025
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Robert Hausler (Supervisor)