Enhancing the production of renewable petrochemicals by co-feeding of biomass with plastics in catalytic fast pyrolysis with ZSM-5 zeolites

Abstract

This study investigated catalytic fast pyrolysis (CFP) of a series of biomass (cellulose, lignin, and pine wood), plastics (low-density polyethylene (LDPE), polyethylene (PP), and polystyrene (PS)), and their mixtures with ZSM-5 zeolite. Co-feeding of cellulose with LDPE (mixing ratios of 4–1) produced much higher petrochemical (aromatics and olefins) yields (52.1–55.6 C%) and lower solid (coke/char) yields (22.6–10.9 C%) than those expected if there were no chemical interactions between the two feedstocks in co-feed CFP (37.4–39.2 C% and 25.0–15.9 C% for petrochemicals and solid, respectively, calculated by linear addition of the corresponding yields determined in CFP of cellulose and LDPE individually). This result indicates that cellulose and LDPE have a significant synergy that enhances the production of valuable petrochemicals and decreases the undesired coke in CFP. Similar synergy was also observed in co-feed CFP of pine wood and LDPE mixtures (mixing ratio of 2), which produced 49.5 C% petrochemicals and 19.5 C% solid residue. In comparison, CFP of pine wood and LDPE individually produced only 31.6 C% and 41.0 C% petrochemicals and 46.5 C% and 6.74 C% solid, respectively. This synergy, however, was less pronounced for the other combinations of biomass and plastics (cellulose/PP, cellulose/PS, and lignin/LDPE) tested in this study. The results suggest that the interactions between the primary pyrolysis products of cellulose and LDPE, especially Diels–Alder reactions of cellulose-derived furans with LDPE-derived linear α-olefins, play an important role in the synergy for petrochemical production and coke reduction in co-feed CFP. Co-feeding LDPE thus has great potential in improving the performance of CFP of natural lignocellulosic biomass, which usually contains a significant fraction (40–50wt.%) of cellulose component.