Hydrogen production from biomass and plastic mixtures by pyrolysis-gasification

•H2 has been produced from the pyrolysis/gasification of plastics/biomass mixtures.•Adding plastic to biomass increases H2 content with synergetic interaction.•Polypropylene addition produces higher H2 yield compared to polystyrene.•Addition of Ni/Al2O3 catalyst dramatically improved gas and H2 yield.

The addition of plastics to the steam pyrolysis/gasification of wood sawdust with and without a Ni/Al2O3 catalyst was investigated in order to increase the production of hydrogen in the gaseous stream. To study the influence of the biomass/plastic ratio in the initial feedstock, 5, 10 and 20 wt.% of polypropylene was introduced with the wood in the pyrolysis reactor. To investigate the effect of plastic type, a blend of 80 wt.% of biomass and 20 wt.% of either polypropylene, high density polyethylene, polystyrene or a mixture of real world plastics was fed into the reactor. The results showed that a higher gas yield (56.9 wt.%) and a higher hydrogen concentration and production (36.1 vol.% and 10.98 mmol H2 g−1 sample, respectively) were obtained in the gaseous fraction when 20 wt.% of polypropylene was mixed with the biomass. This significant improvement in gas and hydrogen yield was attributed to synergetic effects between intermediate species generated via co-pyrolysis. The Ni/Al2O3 catalyst dramatically improved the gas yield as well as the hydrogen concentration and production due to the enhancement of water gas shift and steam reforming reactions. Very low amounts of coke (less than 1 wt.% in all cases) were formed on the catalyst during reaction, with the deposited carbonaceous material being of the filamentous type. The Ni/Al2O3 catalyst was shown to be effective for hydrogen production in the co-pyrolysis/gasification process of wood sawdust and plastics.

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