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

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.