Upcycling of polyethylene terephthalate to 1,4-cyclohexanedimethanol in water

The recycling of waste polyethylene terephthalate (PET), an extensively used polymer as plastic and fiber materials, has become an urgent topic due to the rapid generation and accumulation of plastic waste into the environment. Current chemical recycling approaches to depolymerize and convert PET into 1,4-cyclohexanedimethanol (CHDM), an important chemical in the production of advanced polyesters, predominantly use organic solvents, such as alcohols or dioxane. Herein, we developed an environmentally friendly and economically viable pathway for converting PET to CHDM using water as the solvent. In this process, PET is sequentially hydrolyzed in water, hydrogenated to 1,4-cyclohexane dicarboxylic acid (CHDA), and then reduced to CHDM. The PET conversion rate is self-enhanced in aqueous medium via acid-catalyzed hydrolysis by the generated CHDA intermediate. A Pd-based catalyst (e.g., Pd/C) selectively hydrogenates the arene ring of the PET monomer, terephthalic acid intermediate, and a Ru-Sn/C bimetallic catalyst reduces its COOH to CH₂OH group. At optimized reaction conditions, a complete conversion of PET and 80.1% yield of CHDM are obtained. Alternatively, this approach can also efficiently produce CHDA from PET, with a yield up to 86.4%.