Fast and ex Situ Catalytic Copyrolysis of Switchgrass and Waste Polyethylene

Continuous fast and ex situ catalytic pyrolysis of blends of switchgrass with 15 wt % polyethylene (PE) was studied using a fluidized bed pyrolysis system. Higher than typical temperatures for biomass pyrolysis were utilized (630 °C) to overcome the higher thermal stability of polyethylene. For fast pyrolysis, the high pyrolysis temperature led to a lower yield of oil and a higher yield of gas from the switchgrass. When polyethylene was blended in, a small increase in the yield of oil was noted, and the oil had a slightly lower oxygen content and higher hydrogen content. GC/MS and NMR analysis showed that linear alkenes and alkanes were present in the oil in addition to phenolics, acids, and other oxygenates derived from biomass. However, a phase separated wax product was also formed, and this accounted for an estimated 27% of the input plastic carbon. Ethylene was also a major product of PE pyrolysis, accounting for 29% of the input plastic carbon. Only about 19% of the input plastic carbon was in the oil product. When ex situ catalytic pyrolysis was performed over HY at 250 °C, the oil product phase separated into a largely biomass derived fraction and a plastic derived fraction. When the catalysis was performed at 300 °C, there was a shift in reactivity for the blends compared with switchgrass only, decreasing CO formation and resulting in an oil rich in alkyl benzenes, alkyl naphthalenes, and alkyl phenols.