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From Recycled Polyethylene Terephthalate Waste to High-Value Chemicals and Materials: A Zero-Waste Technology Approach
Summary
This paper describes a zero-waste chemical recycling process for polyethylene terephthalate (PET) plastic — one of the most common sources of environmental microplastics — that converts it into useful chemicals (cyclic ketals and terephthalic acid) using inexpensive iron and chromium catalysts. Unlike mechanical recycling, this chemical approach breaks PET down into valuable building-block chemicals, potentially making recycling economically attractive. Reducing PET waste at the source is a key strategy for limiting the volume of microplastics entering soils and waterways.
The presence of PET (polyethylene terephthalate) in the environment is a global problem due to soil and water microplastic contamination. There is a constant demand for new technologies that expand the possibilities of PET disposal or recycling while reducing energy consumption and anthropogenic carbon footprint. In this study, we developed a comprehensive zero-waste management system for PET recycling (rPET) to cyclic ketals and terephthalic acid. The developed method is based on the hydrolysis of rPET flakes in an inert environment with the separation and purification of terephthalic acid and the dehydration of ethylene glycol. For the first time, we present the use of cheap and readily available Cr/SiO2 and Fe/SiO2 nanocatalysts for direct acetalization of ethylene glycol without organic co-solvents. The catalysts were characterized by EDXRF, XPS and TEM techniques. The 2,2-dimethyl-1,3-dioxolane (DMD), a product of ethylene glycol’s direct acetalization with acetone, was tested as a solvent for polymers with satisfactory results in the solubility of epoxy resins. The addition of unpurified terephthalic acid and residues constituting post-production waste to concrete allows for a reduction in the mass of concrete in the range of 11.3–23.4% and the material modified in this way allows for a reduction in concrete consumption. This rPET waste management methodology is consistent with the assumptions of the circular economy and allows for a significant reduction of anthropogenic CO2 emissions.