A study on microwave-assisted chemical recycling of polyethylene terephthalate (PET) waste

A simple and efficient microwave depolymerization methodology to recycle disposable polyethylene terephthalate (PET) was demonstrated. Different conditions of microwave irradiation and sample pretreatments were applied to increase the decomposition yield as well as products quality, and three important products were obtained. Terephthalic acid (TPA) was the major product, and its purity was tested by using it to synthesize metal organic framework (MOF) compounds namely MIL-53-Fe and UIO-66-Zr. The second valuable product was carbon black, which was separated and its specific surface area was 400 m².g⁻¹ after activation. Trisodium phosphate (TSP), another valuable product, was obtained as byproduct when phosphoric acid was used as digester. The yields of TPA were dependent on PET pretreatment routines. They were 64%, 69% and 89% for as received, 100 kGy gamma irradiated and 24 h ultra violet (UV) irradiated PET respectively. These results signified the positive impact of radiation on the yield of depolymerization process. The proposed method and pretreatments are very useful in upcycling of PET bottles and other containers due to the increasing applications of TPA as the main monomer in the industrial production of PET and other engineering materials.