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

A study has been carried out using HZSM-5, HY and H beta zeolite-based catalysts in the pyrolysis of high density polyethylene (HDPE) continuously fed into a conical spouted bed reactor (CSBR) at 500 degrees 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 C11+ 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, approximate to 58 wt% once equilibrated: whereas high yields of non-aromatic C-5-C-11 products (around 45 wt%) are obtained with H beta and HY zeolite-based catalysts. Wax yield increases as reactions proceed, especially with HY and H beta 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. (C) 2008 Elsevier B.V. All rights reserved.