Sustainable Route to High-Quality CHDM from PET Waste: Hydrogenation-Hydrogenolysis of the Ethanolysis Product under Milder Conditions

Upcycling poly(ethylene terephthalate) (PET) waste into high-value chemicals presents an attractive yet challenging goal. This study developed an innovative process that first utilizes the ethanolysis product of PET-diethyl terephthalate (DET) as a key intermediate to convert PET waste into 1,4-cyclohexanediol (CHDM), which is a key ingredient for high-performance polymers. DET was hydrogenated to diethyl 1,4-cyclohexanedioate (DECD) over the Ru/Al2O3 catalyst, achieving a 98% yield at 130 °C and 3 MPa H2. DECD was then hydrogenolyzed into CHDM on the Cu/ZnO/Al2O3 catalyst. By optimizing the ZnO loading, the hydrogenolysis efficiency was enhanced, enabling the reaction to proceed at lower temperature and hydrogen pressure. The resulting CHDM achieved a trans/cis ratio of 4.1, significantly higher than that of commercial CHDM (trans/cis = 3.14). Furthermore, the process was validated to effectively handle various postconsumer PET plastics, with an overall yield exceeding 91.2% for converting PET into CHDM. This research holds significant importance for advancing the polyester value chain and promoting a renewable future.