Hydrogen rich reducing gases generation in the production of charcoal from woody biomass carbonization

Highlights: • High temperature slow pyrolysis of eucalyptus wood + catalytic upgrading of vapors. • Catalysts performance: Ni/CeO₂-Al₂O₃ > Katalco 57-4Q > Ni/HZSM5 > HZSM5. • Homemade Ni/CeO₂-Al₂O₃ catalyst produces no tars and CO + H₂ rich gases. • High quality charcoal for metallurgical applications. - Abstract: The metallurgical industry uses fossil carbonaceous materials in order to fulfill the high energetic demand of its processes, involving the emission of great amounts of CO₂ that contribute to the greenhouse effect. These CO₂ emissions can be mitigated by using biomass derived fuels and products due to their CO₂-neutral condition. The objective of this paper is to study the carbonization process of woody biomass with the aim of producing a metallurgical grade charcoal and at the same time, a gas reducing agent with a high proportion of H₂ + CO through the thermo-catalytic treatment of the pyrolysis vapors. The experiments were performed using two reactors connected in series. The first one was a semi-batch non stirred 3.5 L reactor swept with 1 L min¹ N₂, where pyrolysis took place at 750 °C. The second one, directly connected to the first reactor, was a tubular reactor where the thermal and/or catalytic treatment of the pyrolysis vapors took place at 900 °C. The sample used for the experiments was eucalyptus trunk wood and to improve the yield and quality of the pyrolysis gases, the following catalysts were tested: commercial HZSM5 zeolite, as received and modified with nickel, a commercial Ni-containing steam reforming catalyst (Katalco 57-4Q), and a homemade Ni/CeO₂–Al₂O₃ catalyst. As a general rule, the catalysts tested had a beneficial effect in the process: they reduced liquid yields, increased gas yields, raised the H₂ content and decreased the CO, CO₂ and CH₄ content in the gases. The positive effect of the catalysts increased in the following order: HZSM5, Ni/HZSM5, Katalco 57-4Q and the homemade Ni/CeO₂-Al₂O₃ catalyst.