Process development and prospective life-cycle assessment of the mechanochemical depolymerization of polyethylene terephthalate

Abstract

• Experimental mechanochemical PET depolymerization and simulated downstream recovery. • 98 % PET depolymerization under ambient conditions of temperature and pressure. • The developed near-zero-waste process recovers high-purity TPA, EG and Na 2 SO 4. • LCA of PET mechanochemical recycling and consecutive downstream process. • Credits for products recovery offset environmental impact of evaluated indicators. PET (Polyethylene-terephthalate) stands out among the most used polymers to produce single-use packaging. While its physicochemical characteristics make it ideal for its intended purpose, they become challenging in the context of waste management. This has prompted research into innovative recycling methods, such as the mechanochemical depolymerization of PET, which has the potential advantage of using only stoichiometric amounts of reagents and to be conducted under ambient conditions of temperature and pressure. As an example, an alkaline hydrolysis of PET is performed in a laboratory-scale high-energy mixer mill within a liquid-assisted-grinding approach. The depolymerization products were recovered using filtration and cooling crystallization techniques and subsequently characterized by 1 H NMR, FTIR, and XRF analyses. A scaled-up process is developed in Aspen Plus®, allowing the comparison of the mechanochemical PET recycling with PET-waste incineration and conventional TPA (terephthalic-acid) synthesis. The conducted prospective LCA shows that the mechanochemical recycling and subsequent products purification have the highest environmental benefit. Despite the environmental burdens associated with the use of electrical energy and chemicals such as sulfuric acid and sodium hydroxide within the process, the negative impacts are offset by the environmental credits obtained from the recovery of TPA, EG (ethylene–glycol) and Glauber salt

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