【作者】 贾延华；

【导师】 张东；

【作者基本信息】 温州大学 ， 应用化学， 2010， 硕士

【摘要】 随着人们环保意识的加强以及聚酯降解问题不断引起世人的关注,对于聚酯解聚反应特性和解聚规律的进一步认识显得更为重要。到目前为止,聚酯PET降解的研究主要处在优化反应条件、选择最佳催化剂等阶段;聚酯降解机理研究远落后于聚酯回收技术水平,在一定程度上制约着聚酯降解工艺的发展。我们已对微波环境下无催化水解PET的反应机理和动力学等进行了大量研究,以期待为催化解聚反应的实际应用提供理论依据。此外,对进一步明晰化学反应中微波效应也具有重要的科学意义。本文主要研究聚酯PET在微波功率为260W,水与PET质量比为10:1 ,催化剂(醋酸锌、氧化亚锡、硫酸锌)为0.5% ,三个温度(190℃、180℃、170℃)中不同反应时间的催化解聚过程。通过对单体产物及残留物的测定、分析和表征来跟踪反应,研究其相应催化体系下的反应机理,并建立相应的动力学模型。采用电位滴定仪对各催化体系中PET解聚的单体产物量(TPA)和残留物PET的端羧基含量进行测定,而其未解聚完的残留物分子量则以端基法进行计算,同时对残留物进行扫描电镜(SEM)、红外(IR)、热分析(TG-DSC联用)等各种分析,以此研究各催化体系的解聚程度和催化解聚残留物的形貌情况。由催化解聚产物单体和残留物端羧基浓度含量的测定可以看出,相同催化剂和反应温度体系下,产物单体TPA浓度随反应时间的推进而增加,残留物端羧基浓度随反应时间的增加而先增后减。在相同催化剂和反应时间的体系下,温度越高产物羧基浓度越高。产物单体、残留物的端羧基浓度与反应时间的递增并不是线性正比关系,而是出现一定的突跃性变化。用端羧基分析方法计算催化解聚残留物的数均分子量(Mn),其结果显示PET大分子链在特定时间段内迅速断裂,而其分子量随时间的推进不断降低并逐渐趋向于稳定。综合各种分析技术的(FT-IR、TG-DSC、SEM)结果可知,在PET的催化解聚过程中,分子链断裂方式是有规-无规-有规催化解聚的循环过程。由分析结果可将解聚反应以分子链断裂方式分为无规和有规两个阶段。无规解聚随反应温度的升高更容易进行。在相同催化剂体系下,建立阶段性的催化解聚反应速率方程,并计算相应的速率常数和活化能。结果表明:微波环境下,催化解聚要比无催化剂的反应活化能都要低些,原因可能是微波的特殊加热和非热效应与催化剂之间的协同效应致使聚酯解聚反应更容易进行。更多还原

【Abstract】 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.更多还原