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

[Display omitted] • The tandem hydrotreatment process was initially proposed to produce biomethane. • Ni/NiAl 2 O 4 catalyst yielded 77.7% CH 4 with 97.8% selectivity from pine sawdust. • The tar and CO x intermediates were fully converted into CH 4. • The optimized temperatures: hydropyrolysis at 550 °C, hydrotreatment at 350 °C. • Increasing reaction pressure to 1.2 MPa shifted dominance to cycloalkanes. This study investigated hydropyrolysis and subsequent vapor-phase hydrotreatment over a NiAl 2 O 4 catalyst to produce biomethane (CH 4) from pine sawdust. The non-catalytic pressurized hydropyrolysis generated tar, CO 2 , and CO as the primary products. However, using a NiAl 2 O 4 catalyst in the second-stage reactor significantly increased the formation of CH 4 and reduced CO and CO 2 in gas products. The catalyst also fully converted tar intermediates to produce CH 4 , resulting in a maximum carbon yield of 77.7% with 97.8% selectivity. The temperature plays a crucial role in CH 4 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 CH 4 , 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. [ABSTRACT FROM AUTHOR]