| As excellent polyester material,poly(ethylene terephthalate)(PET)are widely used in various fields.With the broadening of application areas,the amount of waste PET is growing rapidly,and how to solve the environmental problem of plastic pollution efficiently has become imminent.The recovery of PET by glycolysis is the current focus of businesses and researchers.However,due to the long reaction time,the metal-containing catalyst,the product with high chromatic value is difficult to separate from the metal-containing catalyst,which increases the recovery cost.In this study,combining the advantages of microwave heating technology and high-efficiency catalysis of ionic liquids(ILs),a method for efficiently microwave glycolysis of PET catalyzed by metal-free ILs is proposed,which provides a new idea for the green and high-efficiency degradation of PET.At the same time,a research method to degrade PET under milder conditions in a homogeneous system is also proposed.The main obtained results are as follows:(1)ILs with[Emim]+(1-ethyl-3-methylimidazolium)([Emim][OAc],[Emim][N(CN)2],[Emim][NTf2])were used in PET microwave glycolysis.The activity evaluation results were:[Emim][OAc]>[Emim][N(CN)2]>[Emim][NTf2].Using[Emim][OAc]as a catalyst,the effects of microwave and oil bath heating methods on PET glycolysis were compared.And the results showed that,compared with oil bath heating,PET microwave glycolysis can significantly shorten the reaction time,increase the yield of the product bis-(hydroxyethyl)terephthalate(BHET),and improve the color of the product.Under optimal conditions(PET:EG=1:4,3 wt%Cat.,microwave 600 W,atmospheric pressure,5 min),the conversion of PET was 100%and the yield of BHET reached up to 88.8%.The results of the kinetics study showed that the PET microwave glycolysis accorded with the first-order reaction model,and the apparent activation energy was 377.6k J/mol.This article proved“the non-thermal effect”of microwave didn't exist in PET microwave glycolysis,and microwave heating accelerated the degradation rate by strengthening the polar intermolecular bond vibration to accelerate the fracture.The possible reaction mechanism of PET microwave glycolysis was proposed,and the catalytic effect of alkaline ILs on the PET microwave glycolysis was verified.(2)A method for dissolving PET to achieve efficient homogeneous microwave glycolysis of PET under mild reaction conditions was proposed.N-methylpyrrolidone(NMP)was selected as solvent for homogeneous microwave glycolysis of PET.The results showed that the addition of NMP didn't change the degradation products,and the reaction time was greatly shortened in a homogeneous system,which could achieve rapid and efficient glycolysis of PET under milder conditions.At 180?,3 wt%Cat.,microwave 600 W,PET:EG:NMP=1:2:2,atmospheric pressure,when the reaction time was 8 min,the yield of BHET reached up to 77.6%.The results of homogeneous microwave glycolysis of PET once again proved that microwave can accelerate the glycolysis reaction and obtain colorless product. |
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