Sustainable plastic bottle recycling: employing zinc-deposited SBA-15 as a catalyst for glycolysis of polyethylene terephthalate

Abstract

<abstract> <p>Novel catalysts for recycling PET bottles into monomers have been developed by depositing zinc onto the surface of SBA-15, mitigating ZnO catalyst agglomeration in glycolysis separation processes to enhance reaction yields. Various zinc compounds (Zn(OAc)<sub>2</sub>, ZnCl<sub>2</sub>, and ZnSO<sub>4</sub>) were employed as substrates for catalyst design on the porous, high-surface-area material SBA-15 <italic>via</italic> impregnation. The presence of distinct Zn species on SBA-15 was confirmed through XRD and EDS analyses. The acidity of the catalyst, a crucial factor in the PET glycolysis process, was assessed using different Zn-containing precursors. NH<sub>3</sub>-TPD measurement has revealed the highest acidity in ZnCl<sub>2</sub>, followed by Zn(OAc)<sub>2</sub> and ZnSO<sub>4</sub>, respectively. Glycolysis reactions with a PET:EG ratio of 1:5 and a 1% catalyst at 200℃ for 2 hours revealed the catalytic efficacy of zinc-deposited compounds in the sequence ZnCl<sub>2</sub> > Zn(OAc)<sub>2</sub> > ZnSO<sub>4</sub>. Surprisingly, the ZnCl<sub>2</sub> catalyst produced the highest yield of <italic>bis</italic>-2-hydroxyethyl terephthalate (BHET) at 75% and displayed exceptional recycling capability over three cycles, contributing significantly to resource recovery objectives aligned with the Sustainable Development Goals (SDGs).</p> </abstract>