Nickel-catalysed pyrolysis/gasification of biomass components

Hydrogen and syngas production have been investigated from the pyrolysis/gasification of biomass components (cellulose, xylan and lignin) in the presence of Ni-based catalysts by using a two-stage fixed-bed reaction system. Biomass samples were pyrolysed at the first stage and the derived products were gasified at the second stage. The Ni–Mg–Al and Ni–Ca–Al catalysts, prepared by co-precipitation, were applied in the gasification process. The lignin sample pyrolysed with more difficulty (56.0 wt.% of residue fraction) compared with cellulose and xylan at 500 °C, and therefore resulted in the lowest gas yield (42.7 wt.%) for the pyrolysis/gasification of lignin. However, the highest H2 concentration from the three types of feedstock (55.1 vol.%) was collected for the lignin sample in the presence of steam and catalyst. Carbon deposition was very low as indicated from the TPO and SEM analyses of the reacted Ni–Mg–Al catalyst. The investigation of reaction conditions showed that water injection rate (0.02 and 0.05 g min−1) had little influence on the gas production from the pyrolysis/gasification of lignin in the presence of the Ni–Ca–Al catalyst; however, the increase of gasification temperature from 700 to 900 °C resulted in a higher gas and hydrogen production due to the promotion of secondary reactions during the gasification process. Furthermore, coking was highest for the reacted Ni–Ca–Al catalyst at the gasification temperature of 800 °C (7.27 wt.%), when the temperature was increased from 700 to 900 °C. This work shows that the components of biomass have a significant influence on the catalytic gasification process related to hydrogen and syngas production.

► Highest gas yield occurred for catalytic steam pyrolysis/gasification of cellulose.
► Highest concentrations of hydrocarbon gases was obtained for lignin.
► Ni–Mg–Al catalyst suffered negligible coke deposition.
► Gasification temperature of 900 °C generated highest hydrogen and lowest coke.