Catalytic fast pyrolysis of waste battery separators with limited removal of the AlO layer for selective aromatic hydrocarbons production over HZSM-5 catalyst.

Waste battery separators typically feature a "sandwich" structure made of plastic substrates and AlO layers, which are stable and difficult to degrade or recycle. To address this, a novel method was developed for the directional degradation and high-value conversion of waste plastics, combining alkaline pretreatment with catalytic pyrolysis, promoting the efficient and valuable recycling of waste battery separators. Specifically, alkaline washing was applied for the pretreatment of the AlO-layered separators to control the limited removal of the AlO layer. Aromatic hydrocarbons (AHs) were subsequently produced by pyrolysis using a HZSM-5 catalyst. Pyrolysis-gas chromatography/mass spectrometry was used for the systematical evaluation of the effects of pretreatment and pyrolysis conditions on AHs production. The findings demonstrated the limited removal of the compact AlO layer through alkaline pretreatment enhanced the synergistic catalytic effect of AlO and HZSM-5. This not only promoted the release of volatile components and their decomposition into more light olefins catalyzed by AlO, but also enhanced the subsequent conversion of light olefins into AHs catalyzed by HZSM-5. Optimal conditions included a 0.050 mol/L NaOH concentration, a 650°C-pyrolysis temperature and a catalyst/sample ratio of 12, achieving an AHs yield of 89.89 wt% (on dry ash-free basis). This yield was considerably higher than the 60.40 wt% achieved from untreated separators and the 65.61 wt% from pure polyethylene separators. This study laid a solid foundation for the efficient and high-value recycling of waste battery separators.