Green microwave assisted hydrolysis of PET bottle waste for MIL53 (Al) synthesis: Characteristic, Taguchi optimization

Polyethylene terephthalate (PET) is one of the most widely produced polymers, extensively used in packaging and beverage industries. However, its low recyclability leads to significant environmental challenges, with less than 10% of global plastic waste effectively recycled, while the majority accumulates in landfills or the natural environment. Developing efficient chemical recycling strategies is therefore essential to mitigate environmental impact and recover valuable resources. Among these, depolymerization of PET into terephthalic acid (TPA) offers a promising route for generating a monomer that can be reused in the synthesis of advanced functional materials.
In this study, PET waste was depolymerized into TPA using microwave-assisted alkaline hydrolysis. A Taguchi experimental design was employed to optimize key process parameters, including temperature (160–200 °C), reaction time (5–90 min), PET particle size (0.2–2 cm), PET-to-liquid ratio (1:10–1:2), and microwave power (up to 630 W). Kinetic parameters of the hydrolysis reaction were also determined to better understand the depolymerization mechanism. Under the optimized conditions—190 °C, 90 min, 0.2 cm PET particle size, 10% PET-to-liquid ratio, and 630 W—a maximum depolymerization efficiency of 65% was achieved. The influence of process variables was ranked as reaction time > temperature > particle size > solid-to-liquid ratio.
The recovered TPA was subsequently used as an organic linker for the microwave-assisted synthesis of MIL-53(Al). Structural and textural characterization by XRD, FTIR, BET, and SEM confirmed the successful formation of a porous framework, showing that synthesis and activation conditions significantly influenced crystallinity, surface area, and morphology. This study demonstrates a sustainable strategy for PET valorization, combining process optimization with the production of advanced metal–organic frameworks, and contributes to circular economy initiatives.