Deactivation by coking of industrial ZSM-5 catalysts used in LDPE pyrolysis and regeneration by ozonation process – Bench scale studies

Abstract

Study of the catalytic deactivation during successive uses of ZSM-5 catalysts in bench-scale pyrolysis of low-density polyethylene (200:20 g LDPE:ZSM-5) has been carried out in a semi-batch reactor at 450 °C. The correlation between coke formation over catalyst properties and selectivity during pyrolysis is observed. The loss of catalytic performances translates into a significant drop of aromatics and an increase of waxes in pyrolysis products. The observed deactivation is due to the formation of heavy coke over the catalysts, causing surface hindering, porosity blockage and acid sites diminution. The capacity of ozonation process to regenerate such coked catalysts around 100 °C is demonstrated using a fixed bed reactor. Different times of exposure are investigated to evaluate ozonation efficiency. By using this coke oxidizing treatment during 48 h, regenerated catalysts recovered their initial textural and chemical characteristics (porous volume and acidity) as well as their catalytic performances (similar aromatics proportion as the first pyrolysis).