Chemical recycle of polyester waste using novel zwitterionic catalysts
Waste poly (ethylene terephthalate) (PET) from drink bottles wasdepolymerized using novel zwitterionic imidazolium-2-carboxylate salts ascatalysts (or catalyst-precursors) in the presence of ethylene glycol viaglycolysis to give bis(hydroxyethyl)terephthalate (BHET). The influence ofreaction temperature, glycolysis time, ethylene glycol:PET ratios, and theamount of the zwitterionic imidazolium-2-carboxylate catalysts used on theconversion of PET, isolated yield of BHET, and the selectivity of BHET in theglycolysis of PET were investigated. The results demonstrate that 1,3-dimethylimidazolium-2-carboxylate can bean effective basic catalyst for PET glycolysis, with PET depolymerization of upto 100% observed. BHET was isolated from the reaction mixture with yields ofup to 61.0% under the optimum reaction conditions using 0.15 g catalyst to 1.0g PET in the presence of 10.0 g ethylene glycol (0.15:1:10 mass ratio) at 185oCin 1 h. This is the first time that 1,3-dialkyl-imidazolium-2-carboxylates havebeen reported to be catalysts for glycolysis of PET and, compared to 1,3-dialkylimidazolium acetate ionic liquids, were more effective as catalyst in theglycolysis. The purified monomer was characterized by the nuclear magneticresonance (NMR), mass spectrometry, and high performance liquidchromatography (HPLC).
Poly (ethylene terephthalate) (PET), bis (hydroxyethyl) terephthalate (BHET), glycolysis, carbene, zwitterionic catalyst, imidazolium2-carboxylate (NHC-CO2)
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