Cosolvent-promoted selective non-aqueous hydrolysis of PET wastes and facile product separation

Abstract

The accumulation of polyethylene terephthalate (PET) wastes has caused severe environmental pollution and resource waste due to its widespread use. Hydrolysis of waste PET into terephthalic acid (TPA) is a promising recovery approach and can be a valuable supplement to the route starting from the petrochemical industry. However, the main roadblocks include low-efficiency degradation and tedious/eco-unfriendly separation. Herein, we develop a mild non-aqueous hydrolysis for the selective ester cleavage of PET and facile product separation. This work applies ethylene glycol (EG, one of the monomers for PET polymerization) and tetrahydrofuran (THF) as the reaction solvent to obtain the hydrolysis product terephthalate in the presence of KOH. 100% of PET degradation and 97.5% of TPA yield can be achieved at 60 °C in 1 h. The addition of THF promotes mass transfer by etching of the PET surface while it makes the product auto-precipitate from the degradation solution sufficiently. Besides, THF showed an activating effect on the hydroxyl group of EG, and the ester bonds of PET were cleaved due to a synergy of potassium hydroxide and alkoxide. The degradation even took place at 30 °C. There was no decline in the degradation rate of PET after the degradation solution was recycled 5 times. The cosolvent system can also accomplish the selective degradation of PET into TPA while spandex remained unchanged for colored waste blended textiles. Besides, the system showed excellent elution properties for dyes on the textiles and made it possible to recycle complex wastes. This work provides a promising approach for the efficient and selective degradation of PET, as well as simple product separation by introducing a cosolvent and also provides a useful reference for the recycling of other waste polymers containing ester groups.