Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis

• Published in: Angewandte Chemie International Edition 2022-02, Vol.61 (9), p.e202112576-n/a
• Main Authors: Kratish, Yosi, Marks, Tobin J.
• Format: Article
• Language: English
• Subjects: Butane; Carboxylic acids; Catalysis; Catalysts; chemical recycling; Dicarboxylic acids; Ethane; hydrogenolysis; Naphthalene; PET; Plastic debris; Polybutylene terephthalate; Polybutylene terephthalates; polyester plastics; Polyester resins; Polyesters; Polyethylene; Polyethylene naphthalate; Polyethylene terephthalate; Polypropylene; tandem catalysis; Terephthalic acid
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202112576

Using a mechanism‐based solvent‐free tandem catalytic approach, commodity polyester plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are rapidly and selectively deconstructed by combining the two air‐ and moisture‐stable catalysts, Hf(OTf)4 and Pd/C, under 1 atm H2, affording terephthalic acid (or naphthalene dicarboxylic acid for PEN) and ethane (or butane for PBT) in essentially quantitative yield. This process is effective for both laboratory grade and waste plastics, and comingled polypropylene remains unchanged. Combined experimental and DFT mechanistic analyses indicate that Hf(OTf)4 catalyzes a mildly exergonic retro‐hydroalkoxylation reaction in which an alkoxy C−O bond is first cleaved, yielding a carboxylic acid and alkene, and this process is closely coupled to an exergonic olefin hydrogenation step, driving the overall reaction forward. Commodity polyester plastics such as PET, PBT, and PEN are hydrogenolytically deconstructed to their starting monomeric carboxylic acids and light alkanes using a solventless tandem catalytic approach. These selective reactions operate near the polymer melting temperature under 1 atm H2 and are compatible with mixed plastics.