Abstract:

Fine impurity particles were separated from the waste plastics at four waste disposal sites and used as additives in the pyrolysis of pure plastics in order to study the effect of impurities on the oil quality during the pyrolysis of non-recyclable waste plastics. The effects of four types of impurities (I₁—I₄) on polyethylene, polypropylene, polystyrene and their mixture were investigated, as well as the role of organics and inorganics in the impurities. The additives increased the concentration of primary components in oil from 65.5% to 79.2%—90.3%. The highest concentration was obtained with impurity sample I₄, collected at a bicycle dismantling plant. I₄ also increased the alkenes in the polyethylene/polypropylene pyrolysis oil by 25.0% and 21.1%, but had no significant effect on polystyrene pyrolysis. The I₄ had 3 effects on the pyrolysis of plastics: inorganic ash acting as a heat carrier, the catalytic effect of specific active ash components and the effect of organics in the impurities. Ash as a heat carrier promoted the cleavage of polymer chains. Active ash components catalyzed hydrogenation and hydrogen transfer reaction. Pyrolysis of the organic components in I₄ produced additional aromatics and alkenes. The study would provide guidance for the pretreatment and oil quality control in the large-scale waste plastic pyrolysis process.

Key words: pyrolysis, waste treatment, polymer, plastic, impurity, oil

摘要：

以从4个典型的废弃物处理场取得的与废塑料掺混的杂质样品作为纯塑料热解过程中的添加剂，研究不可回收废塑料中掺混的杂质组分对塑料热解油品质的影响。研究内容包括4种杂质（I₁～I₄）对聚乙烯、聚丙烯、聚苯乙烯及混合塑料热解的影响以及杂质中的无机和有机组分在热解中分别起到的作用。结果表明，杂质的添加将塑料热解油中主要组分的富集度由65.5%提升到79.2%～90.3%；其中来源于废旧自行车拆解厂的杂质I₄对热解油组成的影响最为显著。I₄使得聚乙烯及聚丙烯热解油中的烯烃含量分别提高了25.0%及21.1%，但对聚苯乙烯的热解没有显著影响。I₄对塑料热解的影响可分为三个方面：无机灰分作为热载体起到的作用、特定活性灰分组分的催化作用以及杂质中有机组分参与热解的影响。灰分作为热载体促进了聚合物分子链的裂解；活性灰分组分能够催化加氢及氢转移等反应；而I₄中有机组分热解提高了油相产物中芳烃和烯烃的含量。该研究将为废塑料规模化热解过程中原料的预处理及热解油品质调控提供指导。

关键词: 热解, 废物处理, 聚合物, 塑料, 杂质, 油