Valorization of Polyolefin/LCO Blends over HZSM-5 Zeolites

Abstract

The cracking of low density polyethylene (PE) and of polypropylene (PP) dissolved in LCO (light cycle oil, product of a commercial FCC unit) is studied in the 450−550 oC range, by using a reactor simulating a FCC riser. The reaction was carried out on catalysts prepared based on HZSM−5 zeolites with different Si/Al ratio The results are explained by the shape selectivity of the HZSM−5 zeolite and by the total acidity, which decreases as the Si/Al ratio of the zeolite is increased. A feed with polyolefin content higher than 5 wt% limits the conversion of LCO. The cracking on HZSM−5 zeolite catalysts of PE/LCO and PP/LCO blends produces a yield of C5−C12 fraction, which is highly aromatic and with a high content of styrene, and a low yield of C1 and C2 gases and of coke. A feed made up of polyolefins and LCO contributes to increasing the yield of light olefins, of which the concentration of ethylene increases with temperature. When compared to the coke selectivity of LCO cracking, a feed with PP contributes to increasing it, whereas PE decreases it.