Methane Production from the Pyrolysis–Catalytic Hydrogenation of Waste Biomass: Influence of Process Conditions and Catalyst Type

The production of methane through the optimization of various operating parameters and the use of different catalysts has been investigated using a two-stage, pyrolysis–catalytic hydrogenation reactor. Pyrolysis of the biomass in the first stage produces a suite of gases, including CO2 and CO, which undergo catalytic hydrogenation in the presence of added H2 in the second stage. The influence of the biomass pyrolysis temperature, catalyst temperature, and H2 gas space velocity has been investigated for the optimization and enhancement of the methane yield. In addition, different metal catalysts (Co/Al2O3, Mo/Al2O3, Ni/Al2O3, Fe/Al2O3), the influence of different metal loadings, catalyst calcination temperature, and different support materials (Al2O3, SiO2, and MCM-41) were investigated. The yield of methane was linked to the properties of the catalysts including the preparation calcination temperature and support material which influenced the catalyst surface area and metal crystallite particle size by sintering. The highest methane yield of 7.4 mmol g–1 biomass was obtained at a final pyrolysis temperature of 800 °C, catalyst temperature of 500 °C, and H2 gas hourly space velocity of 3600 mL h–1 g–1 catayst. This optimization process resulted in 75.5 vol % of methane in the output gaseous mixture.