Towards recycling purpose: Converting PET plastic waste back to terephthalic acid using pH-responsive phase transfer catalyst

Converting polyethylene terephthalate (PET) wastes to its monomer and valuable chemicals via eco-friendly chemical method is still a challenge task. Previously, phase transfer catalysts used for alkaline hydrolysis were soluble in reaction media and hardly separated after reaction. Here, we reported several pH-responsive catalysts combined alkyl quaternary ammonium units with heteropolyacid anion for achieving stepwise product/catalyst separation and catalyst recycling. The properties of homogeneous/heterogeneous transfer behavior allow catalyst to be easily separated from reaction media by adjusting of pH value. Among them, [C 16 H 33 N(CH 3 ) 3 ] 3 PW 12 O 40 (abbreviated as [CTA] 3 PW) exhibits the highest activity and the most suitable pH responsive values. Such a pH triggered switchable catalytic system not only shows good performance for depolymerization of pure PET, but also some real PET wastes such as coloured trays and PE/PET complex films could be completely degraded into terephthalic acid. Additionally, the reaction kinetics and activation energy of PET alkaline hydrolysis also studied with and without pH-responsive [CTA] 3 PW.