Tunable solid-acid catalysts for selective depolymerization of aliphatic polyesters into monomers

Overview

This technology addresses a critical bottleneck in plastics recycling by enabling the selective deconstruction of aliphatic polyesters into reusable monomers. Conventional mechanical recycling degrades polymer quality, while most chemical recycling approaches struggle to process mixed streams efficiently. The proposed solution uses heterogeneous solid-acid catalysts with tunable acidity and structure to selectively cleave carbon-oxygen bonds in polyesters such as polylactic acid (PLA) and poly-hydroxy-alkanoates (PHA) under mild conditions with water. This approach enables sequential depolymerization and recovery of high-purity monomers, including lactic acid and lactides, from both single-polymer and mixed polyester waste streams.

Technical specifications

Key features:

• Tunable acidity: The ratio of Brønsted acid to Lewis acid sites on zeolites and tungstated zirconia can be adjusted to control selectivity toward desired C-O bond cleavage pathways
• Earth-abundant and recoverable: Catalysts are composed of common, sustainable elements and can be recovered and reused after reaction
• Mild operating conditions: Reactions proceed at temperatures between 393 and 523 K in stainless-steel pressurized vessels under nitrogen atmosphere, reducing energy requirements compared to conventional thermal depolymerization
• Versatile substrate scope: Applicable to bio-based polymers including poly-3-hydroxyvalerate (PHV), poly-4-hydroxybutyrate (P4HB), and other poly-hydroxy-alkanoates, as well as PLA
• Mixed-stream compatibility: Designed to tolerate mixed plastics, additives, and contaminants found in real-world waste streams
• Established analytical workflow: Product identification and quantification through gas chromatography and GC-mass spectrometry for both liquid monomers and gaseous byproducts
• Proof-of-concept established: Prior work demonstrated reversible cleavage and formation of C-O bonds in alcohol etherification using the same catalyst family at 393 K

Technology readiness level

The technology is at an early-to-mid stage of development. The underlying catalytic chemistry has been validated through prior work on ether bond cleavage and formation using zeolites and tungstated zirconia, providing a strong proof-of-concept for C-O bond manipulation at mild temperatures. Extension to aliphatic polyester deconstruction is currently in the research phase, with a structured one-year plan to synthesize and characterize candidate catalysts, test them against individual bio-based polymers, and evaluate performance on mixed plastic streams. Current readiness is consistent with TRL 2–3, advancing toward TRL 4 as catalyst performance is demonstrated on realistic polymer feedstocks.