Heterogeneous Metal Azolate Framework-6 (MAF-6) Catalysts with High Zinc Density for Enhanced Polyethylene Terephthalate (PET) Conversion

Abstract

Polyethylene terephthalate (PET) has been extensively used for the fabrication of various packaging materials, creating million tons of waste per year. Degrading and recycling PET waste has been identified as a prominent issue. Herein, we demonstrate an effective process to chemically convert PET to bis(2-hydroxyethyl) terephthalate (BHET) through the use of metal azolate framework-6 (MAF-6) as a catalyst in the presence of ethylene glycol. MAFs are a subclass of metal−organic frameworks (MOFs), with MAF-6 comprised of the metal ion Zn 2+ and the organic ligand 2-ethylimidazole. We have optimized the reaction temperature, reaction time, and catalyst amount to achieve up to a 92.4% conversion of PET and an 81.7% yield of BHET at 180 °C for 4 h. MAF-6 was easily recovered and reused for at least five times. We have also hypothesized a mechanism for the high conversion and yield of the PET glycolysis reaction catalyzed by MAF-6. The use of MAF-6 as a catalyst opens a new route for the postconsumer recycling of PET with remarkable practicality.

Thermochemical Conversion of Plastic Waste into Fuels, Chemicals, and Value‐Added Materials: A Critical Review and Outlooks

“…In addition, without adding water, the precipitation of BHET was achieved by ethylene glycol (one of the reactants of glycolysis). Very recently, PET glycolysis over a large‐pore metal azolate framework‐6 (MAF‐6) catalyst with EG to generate BHET has been reported [219] . An outstanding catalytic performance, 92.4 % conversion of PET and 81.7 % yield of BHET, was achieved at 180 °C for 4 h of glycolysis in the presence of MAF‐6.…”

Easily recoverable and reusable p-toluenesulfonic acid for faster hydrolysis of waste polyethylene terephthalate

“…2,3 Consequently, from both economic and environmental viewpoints, the development of methods for the recycling and conversion of waste PET into valuable chemicals is essential. 4 To date, a number of chemical recycling routes including enzymolysis, 5 hydrolysis, 6–8 alcoholysis, 9,10 and glycolysis 11–13 have been proposed to upcycle waste PET.…”

Removal of carbon dioxide using zeolitic imidazolate frameworks: Adsorption and conversion via catalysis

“…[ 28 ] The high chemical stability of MOFs, especially against water molecules, is usually required for applications such as gas adsorption of CO 2 from the atmosphere or hot‐flue gases. [ 29 ] MOFs were applied for several applications, including CO 2 adsorption, [ 30 ] chemical conversion/fixation of CO 2 , [ 31–40 ] catalysis, [ 41–43 ] photovoltaic devices, [ 44 ] sensors, [ 45–48 ] hydrogen production, [ 18,49–53 ] dye sensitizing solar cells (DSSCs), [ 54 ] water treatment, [ 55–57 ] energy, [ 58,59 ] and osmotic power generators. [ 60 ]…”