Renewable Eutectic Solvent-based Catalytic Systems for the Chemical Recycling of PET and PEF

INTRODUCTION
Polyester circularity requires recycling technologies able to recover high-quality monomers under milder and more sustainable conditions than those achieved by conventional hydrolysis. The present study addresses that challenge by exploring biobased eutectic solvents as reaction media/catalytic systems for the alkaline hydrolysis of poly(ethylene terephthalate) (PET) and its bioderived analogue poly(ethylene 2,5-furandicarboxylate) (PEF).

METHODS
Eutectic solvents based on choline chloride and natural phenolic compounds were combined with sodium carbonate and water to promote polyester hydrolysis. PET was used as a model substrate for screening and optimization by design of experiments, after which the optimized conditions were extended to PEF. Recovered monomers were structurally characterized by ATR-FTIR and NMR spectroscopy, and the process was further evaluated through solvent-reuse assays, green metrics, and repolymerization tests. BHET-solvent model system interaction energies were computed using discrete Ab Initio calculations.

RESULTS
The combined presence of eutectic solvent, sodium carbonate, and water was essential for effective depolymerization. Under optimized conditions, PET was converted into terephthalic acid with recoveries above 90%, while PEF was converted into 2,5-furandicarboxylic acid with recoveries above 80%, at temperatures below 150 °C and reaction times under 5 h. The recovered monomers showed high purity, and the eutectic solvent could be reused for at least 7 cycles before loss of catalytic activity. E-factor values in the range of 6-13 were obtained – comparable to those reported for fine-chemical processes – and the recovered monomers were successfully repolymerized into PET and PEF.

CONCLUSIONS
Biobased eutectic-solvent-mediated alkaline hydrolysis provides an efficient and comparatively greener route for polyester chemical recycling, enabling monomer recovery, solvent reuse, and closed-loop repolymerization.

ACKNOWLEDGEMENTS
This work was developed within the scope of the project CICECO Aveiro Institute of Materials, UID/50011/2025 & LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC). The FCT is acknowledged for the research contract to AFS (CEECINSTLA/00002/2022).