Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis.

Area of Science:

• Chemical Engineering
• Materials Science
• Catalysis

Background:

• Polyester plastics like polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are widely used but pose recycling challenges.
• Current recycling methods often involve harsh conditions or result in lower-value products.
• Developing efficient and selective depolymerization methods is crucial for sustainable plastic waste management.

Purpose of the Study:

• To develop a novel, solvent-free catalytic approach for the deconstruction of commodity polyester plastics.
• To achieve high yields of valuable monomers and hydrocarbons from PET, PBT, and PEN.
• To elucidate the reaction mechanism using experimental and computational methods.

Main Methods:

• A mechanism-based, solvent-free tandem catalytic approach was employed.
• Two air- and moisture-stable catalysts, hafnium triflate (Hf(OTf)4) and palladium on carbon (Pd/C), were used in combination.
• The reaction was conducted under 1 atm of hydrogen gas (H2).
• Density Functional Theory (DFT) was used for mechanistic analysis.

Main Results:

• Commodity polyesters (PET, PBT, PEN) were rapidly and selectively deconstructed.
• Essentially quantitative yields of terephthalic acid (or naphthalene dicarboxylic acid) and alkanes (ethane or butane) were obtained.
• The process was effective for both laboratory-grade and waste plastics.
• Comingled polypropylene remained unchanged, demonstrating selectivity.

Conclusions:

• The developed catalytic system offers an efficient and selective method for polyester plastic deconstruction.
• The process yields valuable chemical feedstocks and simple hydrocarbons.
• The mechanism involves a coupled retro-hydroalkoxylation and olefin hydrogenation pathway, driven by mild exergonic reactions.