原位红外光谱研究聚对苯二甲酸乙二醇酯(PET)醇解反应过程

Study of Process of Polyethylene Terephthalate(PET) Methanolysis by FT-IR in situ

以醋酸锌(ZnAc2)为催化剂,甲醇(CH3OH)为醇解剂,采用在线红外光谱仪跟踪了聚对苯二甲酸乙二醇酯(PET)解聚反应过程中产物红外特征峰强度随时间的变化关系,研究了催化剂用量和反应温度对PET解聚过程的影响,并给出了可能的解聚机理。红外光谱跟踪结果表明,解聚过程中C-O,C=O基团的红外吸光强度随时间不断增强,解聚完成后吸光强度趋于定值。同时二者表现出相同的变化趋势,可以用其表征PET的解聚率。通过比较不同反应条件下的PET解聚速率发现,催化剂ZnAc2的适宜用量为PET质量的0.8%;提高反应温度可显著缩短PET解聚所需的时间,在190℃条件下,PET完全解聚仅用时15 min,具有良好的工业应用价值。PET解聚的主要产物是对苯二甲酸二甲酯(DMT)和乙二醇(EG),解聚过程中PET存在多种断链机制,产生不同的中间产物,可继续与甲醇发生酯交换反应生成DMT和EG。

The process of polyethylene terephthalate（PET） alcoholysis was monitored by means of FT-IR spectrometer in situ.Using zinc acetate（ZnAc2） as the catalyst and methanol（CH3OH） as the alcoholysis reagent,the relationship between the IR peaks intensities of the reaction products and the reaction time was studied.Additionally,the influence of the used catalyst dosage and reaction temperature on the PET depolymerization process was investigated,and a possible mechanism of depolymerization was given.Infrared tracking results show that the infrared absorption intensities of C-O,C=O groups increase with the reaction time during the depolymerization process and tend to be respective constants after complete depolymerization.Based on this,the infrared absorption intensity of C-O,C=O groups can be used to characterize the PET depolymerization rate.It was found that the best used dosage of the catalyst ZnAc2 is 0.8% of the mass of PET.The time required for complete depolymerization can be greatly shortened when the reaction temperature is increased.At 190℃,PET can be depolymerized completely in only 15 min,it has a good industrial application value.There are several chain scission mechanisms in PET depolymerization process,the chain scissions of PET can produce different intermediates which can continually react with methanol to generate dimethyl terephthalate（DMT） and ethylene glycol（EG） through transesterification reaction with methanol.