Hydrogen Production through Intermediate Pyrolysis and Thermo-Catalytic Reforming of  Forestry and Agricultural Residues
Creators: Cumpa Millones, Enrique J
Publisher: name: University of Alberta Library
Year: 2024

<p>Hydrogen, a clean energy carrier, is essential for achieving net zero emissions in the energy sector by 2050 and limiting global warming to 1.5 °C. Current hydrogen production relies on fossil fuels, but shifting to renewable sources is an important opportunity. The thermochemical conversion of biomass waste offers a promising alternative for green hydrogen production. In particular, the process which integrates intermediate pyrolysis and thermal reforming, offers the flexibility to optimize both the yield and quality of the products, to obtain hydrogen-rich syngas, high-quality bio-oil, and high-quality biochar. This study investigates the potential of hydrogen production from forest and agricultural residues using an intermediate pyrolysis process, through experimental investigation including the characterization of feedstocks and products. Also, this research aims to quantify the hydrogen and volumetric syngas produced per kilogram of feedstock. The study evaluates the effect of reformer temperatures on the yield and quality of syngas, bio-oil, and biochar.In the first part of this study, softwood (SWPs) and hardwood pellets (HWPs) were processed in a 2 kg/h reactor (TCR®-2) at different intermediate pyrolysis temperatures (i.e., 400 °C, 450 °C, 500 °C, and 550 °C), and reformer temperatures (i.e., 500 °C, 600 °C, 650 °C, and 700 °C). The reformer temperature has more influence on the yield and quality of the products than intermediate pyrolysis. At higher process temperatures, the syngas yield increases, while the bio-oil, biochar, and aqueous phase yields decrease. However, the quality of the products improves at elevated temperatures. The highest H2 yield from SWPs was 24.46 g H2/kg dry biomass obtained at 550 °C in the intermediate pyrolysis reactor and 700 °C in the reformer. Similarly, the highest H2 yield from HWPs was 24.47 g H2/kg dry biomass, obtained at 450 °C in the intermediate pyrolysis reactor and 650 °C in the reformer. Furthermore, the highest volumetric syngas yield was obtained at 550 °C in the pyrolysis reactor and 700 °C in the reformer, for both feedstocks, SWPs (0.79 Nm3/kg dry biomass) and HWPs (0.81 Nm3/kg dry biomass). The H2/CO molar ratios for the syngas for SWPs (0.73-1.21) and HWPs (1.01-1.51) suggest that the syngas can be used to produce Fischer-Tropsch liquid fuels, methanol, and aldehydes via oxo-synthesis. At these high temperatures in the intermediate pyrolysis and reformer reactors, the bio-oil reaches a higher quality with a low total acid number (TAN) (SWP: 9.6 mg KOH/g, HWP: 17.3 mg KOH/g), low kinematic viscosity (SWP: 8.4 cSt, HWP: 3.9 cSt), low O/C molar ratio (SWP: 0.096, HWP: 0.099), high HHV (SWP: 34.56 MJ/kg, HWP: 35.18 MJ/kg), low phenols values (SWP: 23.09 %, HWP: 14.67 %), and high content of polyaromatic hydrocarbons (PAHs) (SWP: 34.34 %, HWP: 39.52 %) and monoaromatic hydrocarbons (MAHs) (SWP: 17.93 %, HWP: 18.88 %). Similarly, the biochar quality improves at higher temperatures, reaching a low H/C (SWP: 0.128, HWP: 0.121) and low O/C (SWP: 0.008, HWP: 0.016).In the second part of this study, wheat straw pellets (WSPs) were processed at three intermediate pyrolysis (i.e., 450 °C, 500 °C, and 550 °C) and three reformer (i.e., 600 °C, 650 °C, and 700 °C) temperatures in a TCR-2 unit. The highest H2 (19.06 g H2/kg dry biomass) and volumetric syngas (0.63 Nm3/kg dry biomass) yields were found at 550 °C and 700 °C, in the intermediate pyrolysis and reformer, respectively. H2/CO molar ratios between 1.06 and 1.17 indicate that the syngas can be further processed for Fischer-Tropsch synthesis, methanol, and oxo-synthesis. Furthermore, bio-oil and biochar qualities are enhanced at these elevated temperatures. The bio-oil achieves the highest quality, indicated by a low TAN (15.6 mg KOH/g), low kinematic viscosity (12.5 cSt), low O/C molar ratio (0.067), high HHV (37.28 MJ/kg), low phenolic compounds content (9.60 %), and high PAH content (61.76 %). Likewise, the biochar reaches a low H/C (0.128) and low O/C (0.065).The findings from this study provide valuable insights into the potential for hydrogen and H2-rich syngas production from forestry residues (SWPs and HWPs) and agricultural residues (WSPs) through thermo-catalytic reforming technology. Moreover, this research highlights potential applications for the enhanced quality bio-oil and high-quality biochar generated in the process.</p>