Coupling hydropyrolysis and vapor-phase catalytic hydrotreatment to produce biomethane from pine sawdust

This study investigated hydropyrolysis and subsequent vapor-phase hydrotreatment over a NiAl₂O₄ catalyst to produce biomethane (CH₄) from pine sawdust. The non-catalytic pressurized hydropyrolysis generated tar, CO₂, and CO as the primary products. However, using a NiAl₂O₄ catalyst in the second-stage reactor significantly increased the formation of CH₄ and reduced CO and CO₂ in gas products. The catalyst also fully converted tar intermediates to produce CH₄, resulting in a maximum carbon yield of 77.7% with 97.8% selectivity. The temperature plays a crucial role in CH₄ generation, with both its yield and selectivity showing a positive correlation with the reaction temperature. Increasing the reaction pressure from 0.2 to 1.2 MPa notably inhibited the production of CH₄, leading to a shift towards cycloalkanes due to a competitive reaction. This tandem approach shows great potential as an innovative technique for producing alternative fuels from biomass wastes.