Conversion of a used poly(ethylene terephthalate) bottle into oxalic acid and terephthalic acid by oxygen oxidation in alkaline solutions at elevated temperatures

Chemical recycling of poly(ethylene terephthalate) (PET) flakes to terephthalic acid (TPA) and oxalic acid was investigated by simultaneous hydrolysis and oxygen oxidation in concentrated NaOH. PET flakes were hydrolyzed to sodium terephthalate and ethylene glycol (EG) in NaOH solutions before oxygen introduction. Because sparingly soluble sodium terephthalate in concentrated NaOH solutions was stable to the oxidation, the TPA yield was approximately 100 mol % under all conditions. In contrast, EG was oxidized to oxalate and CO₂, and the maximum oxalic acid yields were 60.7 mol % using flakes from the bodies of transparent bottles and 65.9 and 71.4 mol % using commercial transparent flakes and a mixture of transparent and green flakes from PET, respectively. If the gate fee (83.3¢/kg of PET) can be obtained as a waste PET recycling subsidy from the Japanese government, this process will generate a profit of $1,134.20 for the treatment of 1000 kg of PET as a net profit for 70 mol % of oxalic acid yield.