Kinetics Of Catalysis Hydrolytic Depolym Erization Of Poly (ethylene Terephthalate) Under Microwave Irradiation

With the strengthening of people's awareness of environmental protection and the ingcreasing attention about polyethylene terephthalate (PET) depolymerization, further understanding of PET depolymerization reaction characteristics and accumulation seems more important. Prestently, the study of PET depolymerization is just optimization of reaction conditions, the best catalyst selection stage, etc. the study of depolymerization mechanism is far behind the level of PET recycling technology, and thus to some extent restricting the development of PET depolymerization process. The reaction mechanism and kinetics of hydrolytic depolymerization of PET without catalyzer under the microwave irradiation had been studied. It is expected that the theoretical foundation could been afforded to the practical application of the catalysis hydrolytic depolymerization. Moreover, it is of great scientific significance to further clarify the microwave effect in the chemical reaction.In this thesis, the catalysis hydrolytic depolymerization of PET under microwave irradiation at different times for different temperatures was studied, in which the proportion of water to PET was 10:1and the catalyst was 0.5%of PET. the reaction mechanism and corresponding dynamic model were investigated by the way of analyzing the monomer and residues. In various catalytic systems, the carboxyl concentration of monomer TPA and residues could be measured by potentiometric titration. At the same time, the relative number average molecular weight(Mn) of the residues was determined by end-group method. And then the PET residues were studied by the analytical techniques such as SEM, FT-IR and TG- DSC, etc.Based on experimental results, it could be found that under the same system of catalyst and reaction temperature, The concentration of TPA with reaction time moving forward had increased, the carboxyl concentration of the residues with reaction time increasing had increased first and then decreased. under the same catalyst and reaction time, the concentration of carboxyl group had increased with temperature increasing. The relationship of carboxyl-group concentration versus time did not change by linear Proportion,but had a certain shock.The result of residues Mn which was determined by end-group method showed that the chains of PET moleculars would quickly break into end-group moleculars in a certain period, and the Mn would decrease fast, then tend to stability little by little. Combining with various kinds of the characterization results,it was indicated that in the process of the PET catalysis depolymerization, the way of molecular chain break was the rule-random-rule catalysis degradation course. There would be two different stages, in which one was mainly rule depolymerization and another was the random cleavage degradation happening quickly.With the increase of the reaction temperature,the random chain cleavage degradation reaction was more easily carried out.Under the same catalysis system, the reaction rate equations for different stages were established, respectively. The reaction rate constants and the reaction activation energy were calculated. The results showed that the reaction activation energy with catalyst was much less than the needed energy without catalyst under the microwave irradiation. The reason may be a special synergy among the catalyst, the microwave heating effect and the microwave non-heating effect, which resulted in polymerization of polyester more easily.