Removal of Zn2+ from glycolytic monomers of the polyethylene terephthalate based on electrodeposition

The usage of zinc-containing catalysts in glycolysis causes the residue of Zn 2+ in the polyethylene terephthalate (PET) degradation monomer bis-hydroxyethyl (BHET), which limits the high-value utilization of BHET. This work first used electrodeposition combined with one-time recrystallization to purify BHET. Electrodeposition was suitable for dealing the Zn 2+ concentrations of degradation solutions within 50–100 ppm, and decreased the content of Zn 2+ in BHET from 141.30 to 2.41 ppm, which reached the standard of repolymerization into PET bottles. The removal rate of Zn 2+ was 90 % for the degradation solutions, which decreased the concentration of Zn 2+ in wastewater from 100 to 8.97 ppm. Meanwhile, the Zn 2+ removed from the degradation solutions was deposited on cathode, which obtained metal Zn materials and realized the recycling of Zn resources from Zn(OAc) 2 . Therefore, electrodeposition could realize the purification of BHET, recycling of Zn(OAc) 2 , reducing the environmental pollution caused by the emission of Zn 2+ and the protection of human health, simultaneously. Electrodeposition had less water consumption, lower loss rate of BHET (from 60 % to 10 %) and shorter processing time, compared with six-times recrystallizations. This study first proposed the formation of quadridentate between BHET and Zn 2+ , and put forward a new three-steps electrodeposition mechanism of Zn 2+ : the addition of electric field destroyed the dissociation equilibrium of quadridentate and made it shift to release free Zn 2+ ; the free Zn 2+ gathered to form ionic groups and they migrated to copper; Zn 2+ reduced on copper, of which the first step was the speed limited step.