Continuous microwave co-pyrolysis of LDPE and PET coupled ex-situ catalysis to monocyclic aromatic hydrocarbons using different structural forms of HZSM-5 as catalysts

Continuous microwave co-pyrolysis of LDPE and PET coupled ex-situ catalysis to monocyclic aromatic hydrocarbons (MAHs) using coconut husk-based biochar as absorbent and different structural forms of HZSM-5 including granular HZSM-5 (GH), pelletized HZSM-5 (PH), irregular HZSM-5/SiC foam ceramic (IH) and structured HZSM-5/SiC foam ceramic (SH) as catalysts was investigated. The highest liquid yield of 50.92 wt.% and the highest peak relative content of MAHs of 67.40% were obtained with SH. SH maintained a stable relative content of MAHs in the first 40-min time on stream, which was higher than peak relative content of MAHs with the other three catalysts. This was because the mass transfer of both the reactants and products was enhanced through three-dimensional structure of SiC foam ceramic. However, due to severe acid site loss of SH, catalytic activity rapidly decreased to about 55% of the initial value in the last 20-min time on stream. After regeneration, the physicochemical properties of SH were not restored to the level of the fresh catalyst, indicating an irreversible deactivation, while irreversible deactivation rate gradually increased as 5 run-regeneration cycles proceeded. In comparison, the addition of mesoporous Al₂O₃ in PH diluted catalytic activity of HZSM-5, but it alleviated deactivation of HZSM-5 by playing a role of external coke storage station.