不同醇解聚聚对苯二甲酸乙二醇酯的反应特性

Study on depolymerization of polyethylene terephthalate by different alcohols

分别选择几种常用的一元醇和二元醇为介质,基于在线红外仪监测不同醇解聚聚对苯二甲酸乙二醇酯(PET)的反应过程,研究PET解聚反应特性,比较不同醇解聚PET的反应活性.在线红外分析结果表明,对于不同的醇解体系,在解聚过程中C—O、C=O基团的红外吸光强度均随反应时间不断增强,在解聚完成后吸光强度趋于定值,根据反应体系内C—O或C=O基团吸光强度随时间的变化可表征PET解聚率随时间变化的关系.一元醇解聚PET的反应活性顺序为甲醇﹥乙醇﹥正丙醇﹥异丙醇,二元醇解聚PET的活性顺序为1,2-丙二醇﹥乙二醇﹥1,4-丁二醇.这是因为醇解聚PET是亲核取代反应,在解聚过程中醇的反应活性与分子结构有关,醇的羟基氧原子亲核活性越大、空间位阻越小,解聚速率越快.关于二元醇醇解PET体系,研究反应温度对PET解聚过程的影响,升高温度可以大大缩短二元醇解反应需要的时间,198℃下以PET质量分数1%的醋酸锌为催化剂,1,2-丙二醇完全解聚PET需要40min.

The depolymerization of polyethylene terephthalate （PET） by several common monohydric alco- hols and binary alcohols was monitored by means of FTIR spectrometer in situ. The depolymerization reaction of PET and the reaction activities of different alcohols were investigated and compared. Infrared tracking results show that, for different alcoholysis systems, the infrared absorption intensity of C--O, C=O groups increases with the reaction time during the depolymerization process of PET and tends to be constant after the completion of depolymerization. The PET depolymerization degree vs. time could be characterized by the infrared absorption intensity of C--O or C=O groups vs. time. It was found that the reaction activity order is methanol 〉 ethanol 〉 propanol 〉 isopropanol for monohydric alcohols and 1,2-propylene glycol 〉 ethylene glycol 〉 1,4-butadiene alcohol for binary alcohols. Because the alcoholysis of PET is a nucleophilic substitution reaction, the reaction activities of alcohols are related to their molecular structures. The greater nucleophilic activities of the alcohol oxygen atoms, the smaller the space resist- ance, the faster PET depolymerization reaction. Using binary alcohols, the influence of reaction tempera- ture on PET depolymerization was studied. The increase of reaction temperature can greatly speed up PET depolymerization. Using ZnAc2 with 1 % weight of PET as catalyst,PET can be depolymerized completely