Abstract
A novel chemical recycling method was created to depolymerize waste PET bottles, recover the raw material monomers of PET, namely terephthalic acid (TPA) and ethylene glycol (EG), and afterwards polymerize back to the pure PET using a microwave-assisted process. The depolymerization process was carried out in normal atmospheric pressure, with methanol and sodium carbonate as the reactants used. The following conditions were optimized (95% benzalkonium chloride for the catalyst and 15 h for the reaction time), which gave the highest yields of 85.32% TPA and 82.42% EG. The obtained TPA and EG were purified and then characterized together via Fourier transform-infrared spectroscopy. Afterwards, the TPA and EG produced were converted into bis(2-hydroxyethyl) terephthalate (BHET), and then polymerized into PET using a microwave-assisted polymerization process. Para-toluenesulfonic acid (p-TSA) was used as a catalyst to for re-polymerization of BHET to PET. The microwave power and irradiation time were optimized during PET synthesis. The results showed that highest PET yield was 91.86%, with the optimized conditions of 120 W microwave power and 60 min of irradiation time. The methods were based on the circular economy approach: to recover monomers from PET bottles, which can be used to reproduce PET and generate new products, thereby closing the loop and making the method more sustainable in the long run.
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