The Technical Study Of PET Glycolysis

As we all know,poly(ethylene terephthalate)(PET)is very difficult to be degradated in the environment.Therefore,recovery and reused PET can not only ease the pressure of the environment but also can reduce the waste of resources.Thus,find out a new and efficient catalyst to recovery and reused PET is still the key problem of the present time.In this article,zeolitic imidazolate frameworks(ZIFs)was used as catalysts in PET glycolysis and got good results.Three kinds of ZIFs(ZIF-7,ZIF-8 and ZIF-67)were synthe sized and characterized by FTIR,XRD,TGA,BET and NH3-TPD.Then,they were used as catalysts in PET glycolysis and exhibited excellent catalytic activities.The influences of raw material ratio on the catalytic activity of ZIFs were in vestigated and the optimum results were presented.The results showed that the surface area and acidity of catalyst play important roles in PET glycolysis.When the raw material mole ratio of ZIF-7,ZIF-8 and ZIF-67 were respectively 3:1,4:1 and 4:1,the activity of the catalyst is the highest.Besides,the process technology of the PET glycolysis was studied and the effects of reaction factors,such as reaction temperature,reaction time,the amount of catalyst and the amount of solvent on the conversion of PET and yield of bis(hydroxyethyl)terephthalate(BHET)were also examined.In addition,as solid catalysts,three kinds of ZIFs can be easily separated from the reaction mixture and can be recycled and reused up to three times without significant decrease in catalytic activity.The solvent ethylene glycol(EG)can also be recycled and reused.The main product and by-products were received and characterized and the main product was proved to be BHET monomer and the main by-products were proved to be BHET dimers.At the presence of ZIF-7,ZIF-8 and ZIF-67,the kinetic of PET glycolysis was proved to be first-order and the activation energies were 231.04 kJ/mol,137.64 kJ/mol and 191.63 kJ/mol respectively.