Efficient glycolysis of waste polyethylene terephthalate textiles over Zn-MCM-41 catalysts.

Polyethylene terephthalate (PET), also known as polyester, is extensively utilized in the textile industry. The most commonly used chemical degradation method of PET is ethylene glycol (EG) glycolysis, which enables a closed-loop recovery process suitable for large-scale production. In this study, a new type of heterogeneous catalyst (Zn-MCM-41) was proposed for glycolysis of waste PET textiles, and their catalytic performance is much higher than other mesoporous zeolites. Under optimal reaction conditions, over Zn-MCM-41–25 (Si/Al molar ratio of 25) catalyst PET achieved a conversion ratio of 100 %, with bis-hydroxyethyl terephthalate (BHET) yield reaching 81.4 %. XPS results show that zinc is mainly presented as the state of Zn2+, resulting in excellent stability of the catalyst. HPLC and LCMS analyses were conducted on the products obtained from PET glycolysis, revealing that only a small amount of oligomers were generated during the process. These oligomers primarily consisted of dimer [BHET] 2 and trimer [BHET] 3. The Zn-MCM-41–25 catalyst also demonstrates exceptional performance in colored waste PET textiles glycolysis. Furthermore, we investigated the kinetics of PET glycolysis and determined it to follow first-order kinetics with an activation energy value of 210.03 kJ mol−1. Additionally, HPLC methods was established for analyzing glycolysis products and recovering catalysts using a simple filtration technique. The results demonstrate that even after five cycles, the catalyst maintains its high catalytic activity. [Display omitted] • Heterogeneous glycolysis catalyst with high efficiency and stability for waste PET textiles. • The proposed catalyst can be applied for both colorless and colored textiles. • BHET yield for colorless and colored PET glycolysis can achieve above 94 % and 91 %, respectively. • The potential mechanism of ester chain breaking over Zn2+ active center was proposed. [ABSTRACT FROM AUTHOR]