PET Depolymerization Under Microwave Irradiation And Its Non-isothermal Kinetics Research

Microwave heating technology has been widely applied in various fields, however, the mechanism of it hasn’t been entirely clear, and there is no scientific and unified understanding for the thermal and non-thermal effect of microwave yet. Research on PET hydrolysis under microwave irradiation could explicit the regularity and action mechanism of the non-thermal effect of microwave, to provide the theoretical basis and research methods for the effective and safe use of microwave energy.This thesis studied the depolymerization process of PET under microwave irradiation at 180 ℃ with 260 W(microwave power), 120 Psi(reaction pressure), 10:1(the mass ratio of water and PET), the depolymerization rate was calculated. Using thermogravimetric(TGA) analyzer, combined with integral method and differential method, single and multiple scanning rate method to study the non-isothermal pyrolysis kinetics of the intermediate products of depolymerization, infer the mechanism function and corresponding kinetic parameters which pyrolysis should follow by contrast, discuss the influence of microwave on the depolymerization degree of PET deeply.Obtain the molecular weight and its distribution information of PET chips and undepolymerization PET quickly and accurately by gel chromatography(GPC), to auxiliary explain the reaction mechanism of microwave. At the same time, analyze and characterize the residues combined with infrared(IR), scanning electron microscopy(SEM) and other methods to explore the fracture regularity of PET ester bond under microwave, further explore the non-thermal effect of microwave.The analysis results of non-isothermal kinetics indicated that PET microwave hydrolysis was not a kinetics continuous process in another way, the change of the thermal decomposition activation energy(Ea)presented a certain degree of abrupt decrease. We learned that PET microwave depolymerization was a process from random depolymerization dominated to ruly and random depolymerization simultaneously, and then to ruly depolymerization dominated from TG curve and Ea analysis. A more in-depth study on the mechanism of non thermal effect of microwave was discussed. GPC results showed PET chain ruptured rapidly in a certain reaction time, molecular weight sharply declined, which was consistent with the results of TGA. IR and SEM results showed that the microwave hydrolysis of PET was mainly the rupture of ester bonds, and the depolymerization was conducted inside and outside at the same time, the early stage of the reaction was random depolymerization dominated, and later ruly depolymerization dominated.