Catalytic co-pyrolysis of biomass and waste plastics as a route to upgraded bio-oil

A two-stage reactor system consisting of co-pyrolysis of biomass and plastic in the 1st stage and catalytic upgrading (zeolite ZSM-5 catalyst) of the derived pyrolysis gases in the 2nd stage was used to investigate the yield and composition of the product gases and bio-oil. Biomass waste wood and waste plastics in the form of high density polyethylene, low density polyethylene, polypropylene, polystyrene and polyethylene terephthalate were used as feedstock. The addition of the plastics to the biomass with co-pyrolysis-catalysis, produced a higher CnHm gas yield compared with what would be expected by calculation, suggesting some interaction of the biomass and plastic. The presence of waste plastic resulted in a decrease in the relative proportion of oxygenated compounds in the product oil compared to pyrolysis of biomass alone; for example a reduction of >65% for biomass with polyethylene and polypropylene and >95% reduction for biomass with polystyrene. The fuel properties of the co-pyrolysis upgraded oil were improved compared to biomass alone; for example, the co-pyrolysis of polystyrene and biomass showed an improved relative proportion of compounds in the C5 ― C12 fuel range (76%). In terms of the ratio of biomass to plastic, even low quantities of plastic (9:1 biomass:plastic ratio) produced a lower relative proportion of oxygenated bio-oil compounds, for example biomass:polystyrene at a ratio of 9:1 reduced the relative proportion of oxygenated compounds in the product bio-oil by >55%.