Conversion of HDPE into Value Products by Fast Pyrolysis Using FCC Spent Catalysts in a Fountain Confined Conical Spouted Bed Reactor

Continuous catalytic cracking of polyethylene over a spent fluid catalytic cracking (FCC) catalyst was studied in a conical spouted bed reactor (CSBR) with fountain confiner and draft tube. The effect of temperature (475-600 °C) and space-time (7-45 g_cat min g_HDPE ^-1 ) on product distribution was analyzed. The CSBR allows operating with continuous plastic feed without defluidization problems and is especially suitable for catalytic pyrolysis with high catalyst efficiency. Thus, high catalyst activity was observed, with waxes yield being negligible above 550 °C. The main product fraction obtained in the catalytic cracking was made up of C₅ -C₁₁ hydrocarbons, with olefins being the main components. However, its yield decreased as temperature and residence time were increased, which was due to reactions involving cracking, hydrogen transfer, cyclization, and aromatization, leading to light hydrocarbons, paraffins, and aromatics. The proposed strategy is of great environmental relevance, as plastics are recycled using an industrial waste (spent FCC catalyst).