聚乙烯高压热解及其反应机理研究

High-pressure pyrolysis and its mechanism of polyethylene

塑料废弃物数量日益增加,实现低能耗、高值化利用是促进塑料废弃物回收利用的关键。在380℃设定温度和(1−5)×10^(5)Pa初始压力条件下分别开展聚乙烯高压热裂解和催化热解实验,记录反应过程温度曲线,分析聚乙烯高压热裂解/催化热解产物分布。研究结果表明,反应过程中反应物相态是影响热解反应历程的重要因素;因反应路径而异,压力变化对聚乙烯热裂解和催化热解产生不同程度的影响。聚乙烯高压热裂解实验过程中存在飞温现象,飞温峰值随初始压力的增加呈现单调增加的趋势;峰值温度的升高带来聚乙烯断链程度的加深,即获得更多小分子量产物。在相同设定温度和初始压力条件下的聚乙烯高压催化热解实验中不存在飞温现象,利用锌负载的ZSM-5催化剂实现聚乙烯高选择性制备芳香烃,液体产物中单环芳烃占比达82.53%,积炭产率在1.5%以下。

With the increasing waste disposal problems,high-value utilization technology using less energy is important to incentivize better recycling of plastic waste.Polyethylene high-pressure thermal cracking and catalytic pyrolysis experiments were conducted at a set temperature of 380℃and low initial pressures(1−5)×10^(5)Pa.The process temperature curves were recorded and the hydrocarbon distribution of products was analyzed.The results suggest that the phase state in the pyrolysis system is a critical issue for reaction pathways.Thus,the pressure changes have different effects on the thermal cracking and catalytic pyrolysis of polyethylene.There is a phenomenon of thermal runaway during the polyethylene high-pressure pyrolysis process.The peak temperature represents a monotonous increase with the increasing initial pressure;the higher peak temperature leads to deeper cracking of polyethylene,giving more low-molecular-weight products.In the high-pressure catalytic pyrolysis experiments under the same other conditions,no thermal runaway is observed.The Zn-supported ZSM-5 catalyst converts polyethylene into aromatics,and the selectivity for monocyclic aromatics in the liquid phase is up to 82.53%.Moreover,the coke yield is less than 1.5%.