Nanocrystalline ZSM-5: a highly active catalyst for polyolefin feedstock recycling

摘要

Nanocrystalline HZSM-5 (crystal size around 25 - 60 nm) shows remarkable activity in the catalytic cracking of LDPE, HDPE and PP despite the low temperatures (340 - 380°C) and catalyst loadings used (plastic / catalyst mass ratio = 100). Gaseous hydrocarbons are the main products with a maximum centered at C_4, which are formed through a carbocationic end-chain cracking mechanism. The selectivity towards C_3 - C_5 hydrocarbons is enhanced on decreasing the cracking temperature, reaching a 95 - 100 % at 340°C. PIONA analyses of the liquid hydrocarbons obtained at higher temperatures (380°C) indicate that the highest amount of olefins (47%) is obtained in the cracking of the linear HDPE. In contrast, the branched PP leads mainly towards aromatic compounds (38%).