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

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 C4, which are formed through a carbocationic end-chain cracking mechanism. The selectivity towards C3−C5 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%).