Valorisation of PET-rich mixed plastic waste using a cascading concept involving selective ammonolysis and catalytic...

We report a cascading valorisation strategy for real polyethylene terephthalate (PET)-rich waste streams, combining selective ammonolysis of PET with catalytic pyrolysis of the non-PET residue. In this approach, PET-rich packaging waste is treated with ammonia in ethylene glycol to produce terephthaldiamide (TDA), while the remaining polyolefin (PO)-rich residue is subsequently upgraded to benzene, toluene, xylene (BTX), and light olefins over H-ZSM-5 catalyst. TDA is a valuable aromatic diamide and a potential precursor to p-phenylene diamine, a monomer used in the production of poly(p-phenyleneterephthalamide) (PPTA). For post-consumer PET trays, ammonolysis at 5 bar NH₃, and 100 °C for 8 h, followed by a downstream separation procedure, resulted in an almost quantitative conversion of PET, yielding pure TDA as small crystals in 74 wt% (87 mol%) yield based on the PET content in the feed. The residue (mostly polyolefins) was converted to BTX (5 wt% on residue), and propene/butenes (19 wt%, on residue) using a catalytic in situ pyrolysis approach with H-ZSM-5 at 550 °C. The same strategy was applied to a PET-enriched, DKR-350 mixed-plastic packaging fraction, affording TDA in 71 wt% (87 mol%) yield based on the PET content, while catalytic pyrolysis of the residue produced BTX (3 wt%) and propene/isobutene (4 wt%) based on the residue. These results demonstrate that real PET-rich mixed plastic waste streams can be selectively upgraded into valuable aromatic diamide while retaining the non-PET fraction as a feedstock for petrochemical intermediates.