Catalytic pyrolysis of HDPE in continuous mode over zeolite catalysts in a conical spouted bed reactor

Abstract

A study has been carried out using HZSM-5, HY and Hβ zeolite-based catalysts in the pyrolysis of high density polyethylene (HDPE) continuously fed into a conical spouted bed reactor (CSBR) at 500 °C and atmospheric pressure, with the aim being to assess the yields and composition of the main products (both light olefins and automotive fuel hydrocarbons). Product streams have been grouped into seven lumps: light olefins (C 2–C 4) and light alkanes (<C 4) in the gas fraction, the liquid fraction consisting of three lumps (non-aromatic C 5–C 11 compounds, single-ring aromatics and C 11+ hydrocarbons), wax and coke. The results are compared with those already obtained in thermal pyrolysis in a CSBR and with those obtained in the literature using catalysts in bubbling fluidized beds. HZSM-5 zeolite-based catalyst is very selective to light olefins, ≈58 wt% once equilibrated; whereas high yields of non-aromatic C 5–C 11 products (around 45 wt%) are obtained with Hβ and HY zeolite-based catalysts. Wax yield increases as reactions proceed, especially with HY and Hβ zeolite-based catalysts, due to catalyst deactivation by coke formation. Product distribution with the different catalysts and their evolution throughout continuous operation by feeding HDPE is explained according to the different properties of the zeolites used.