Glycolysis mechanism of efficient catalyzing waste polyethylene terephthalate by zinc acetylacetonate

Glycolysis of polyethylene terephthalate (PET) is an important method to depolymerize PET into bis(hydroxyethyl terephthalate) (BHET), which is of great significance to deal with the problem of recycling waste PET. In order to solve the problems of high temperature, long reaction time and low monomer yield in traditional glycolysis of PET, a new method of efficient depolymerization of waste PET to BHET monomer catalyzed by zinc acetylacetonate was developed. Experimentally, the reaction occurs quickly (30 min) under mild conditions (175℃ and atmospheric pressure) with excellent performance (degradation rate of 100% and BHET monomer yield of 88.1%) as compared with the metal salts and ionic liquids catalyzed reactions. Kinetic studies showed that the catalytic degradation of PET by Zn(acac)2 is in accordance with the shrinking-core model. Infrared spectrum and DFT calculations demonstrated that the active species of the catalytic reaction is Zn(acac)(OCH2CH2OH), which was produced through the ligand exchange between Zn(acac)2 and EG. Glycolysis of PET mediated by Zn(acac)(OCH2CH2OH) takes place through the cooperative functions of Zn2+ and deprotonated ethylene glycol ligand.