低密度聚烯烃在微孔分子筛上的催化裂解及其机理研究

Catalytic pyrolysis of low-density polyolefins on micropore zeolite catalysts and its reaction mechanism

废塑料热解技术是一种将废塑料裂解成燃料和化学品的有效方法,可有效地减少环境污染和发展循环经济。采用具有不同孔径的微孔分子筛H-Y、H-ZSM-5、H-Beta为催化剂,催化裂解低密度聚乙烯（LDPE）和低密度聚丙烯（LDPP）制液体燃料,主要考察微孔分子筛的孔径和酸性对LDPE和LDPP裂解产物的影响,阐明LDPE和LDPP的催化分解机理。结果表明,微孔分子筛的孔径和催化剂的酸性对液体燃料的成分具有重要影响,液体产物的主要成分有烯烃、烷烃、单环的芳香烃化合物、萘酚与其取代衍生物以及茚类化合物。具有最小孔径的H-ZSM-5得到最高收率的芳烃,其碳原子数主要在C7~C11范围,并且单环芳香烃中对二甲苯的含量最高。分子筛中的Brnsted酸位能够显著促进低密度聚乙烯的C—C键的断裂,短链的小分子在分子筛孔道中形成＂碳池＂中间体,这些中间体再经过脱氢和芳构化产生芳香烃化合物,是微孔分子筛促进芳烃生成的主要原因。

The LDPE and LDPP have been pyrolyzed to produce fuels using H-Y,H-beta and H-ZSM-5with different pore sizes as catalysts.The effect of pore sizes and acidity of these micropore zeolites on the products of LDPE and LDPP pyrolysis as well as catalytic pyrolysis mechanism of LDPE and LDPP were investigated.The results showed that the pore size and the acidity of zeolites affected the behavior of LDPE and LDPP remarkably,and the components of the liquid products included olefins,paraffins,monocyclic aromatics,naphethelene and its derivatives,and indenes.HZSM-5obtained the highest yield of aromatics,in which the carbon number ranges from C7to C11with the highest content of p-xylene.It was found that the Brnsted acid site could promote the cracking of C—C bonds and catalyze the dehydrogenation and aromatization of small molecules to aromatics.