(538k) Post-Consumer PET Chemical Recycling into Monomers for the Circular Economy

Plastic pollution is an issue of global concern. Plastic is ubiquitous in human life, used in packaging as well as product manufacturing. Even with the added emphasis on biodegradable polymers, plastic pollution continues to grow around the globe. The pollution has ended up in the ocean, in fish life, the food chain, and humans. One way of limiting plastic pollution is mechanical recycling. However, a significant issue is that the polymer degrades during the process, resulting in a decrease in molecular weight. Chemical recycling is an alternative that transforms the plastic waste into monomers that can be used for repolymerization. The monomers can also be modified to create value-added products. This process is called upcycling and provides a route to circular economy.

Poly(ethylene terephthalate) (PET) is a polymer commonly used in commercial packaging around the world, enabling the creation of bottles, thermoform containers, and textiles. The ester linkages in PET enables chemical degradation through processes such as glycolysis, methanolysis, hydrolysis and ammonolysis. As a model system, the dimethylester of terephthalic acid (DME), dimethyl terephthalate, was converted to terephthalamide (TPA) through reaction with ammonia. Subsequent reduction of TPA yields para-xylylenediamine (PXDA), a monomer useful in making aromatic polyamides. Pseudo first-order reaction rate constants for the conversion of DME to the mono- and bi-functional amide were determined in batch reactions. Experiments conducted from 50 to 125 C enabled determination of the Arrhenius parameters (pre-exponential factors and activation energies). At higher temperatures, the formation of methylated ammonia was observed. Additional experiments on granulated post-consumer PET thermoforms reduced to a particle size between 150-250 microns showed nearly identical reaction kinetics. Preliminary process economics and conceptual design considerations are discussed.