Co-Pyrolysis Behavior of Low-Rank Coal and High-Density Polyethylene Over Zsm-5 Via In-Situ Py-Tof-Ms

Abstract

Catalytic co-pyrolysis of low-rank coal and waste plastic is a prospective method to enhance the pyrolysis products quality. This study investigated the catalytic effects on co-pyrolysis behavior between Hami coal (HM) and high-density polyethylene (HDPE) using a ZSM-5 catalyst, with reaction mechanisms elucidated through in situ Py-TOF-MS analysis. Results revealed that HDPE-derived hydrogen radicals reacted with HM-derived char, promoting secondary cracking and polycondensation reactions to generate polycyclic aromatic hydrocarbons, thereby significantly reducing coal char yield. Meanwhile, the hydrogen radical transfer reacted with phenoxy radicals of HM pyrolysis to form phenolic products, such as benzenediol (m/z=110), methyl-benzenediol (m/z=124), and dimethoxybenzene. C2-C4 were the dominant gas compositions due to the ZSM-5 catalyst's rich pore structure and acid sites; it can accelerate the transfer of hydrogen free radicals and promote secondary cracking of volatiles during catalytic co-pyrolysis. Furthermore, the ZSM-5 catalyst significantly enhanced the alkenes selectivity while simultaneously facilitating aromatization pathways, thereby converting phenolic compounds into n-alkyl benzenes. These results can guide the application of ZSM-5 in the coal and waste plastic co-pyrolysis and optimal tar production.

Keywords: Hami coal, High-density polyethylene, ZSM-5, catalytic co-pyrolysis