Energy & Fuels, Vol.34, No.1, 546-556, 2020
Distinctly Different Performances of Two Iron-Doped Charcoals in Catalytic Hydrocracking of Pine Wood Hydropyrolysis Vapor to Methane or Upgraded Bio-Oil
The catalytic hydrocracking of pine wood hydropyrolysis vapor with two Fe-doped charcoals (Fe/CC-s and Fe/CC-n) was conducted in a two-stage fixed bed reactor at a H-2 pressure of 5 MPa to investigate the catalytic effects on the upgrading of bio-oil and gaseous products. The two catalysts behaved quite differently. Fe/CC-n strongly facilitated the methanation of the volatile matter, resulting in a yield of hydrocarbon gases (mainly CH4) as high as 29.9% (dry biomass basis) at the hydrocracking temperature of 600 degrees C. Fe/CC-s acted as a superior catalyst for bio-oil upgrading. The yields of bio-oil (water free) obtained with this catalyst at 550-600 degrees C reached 20.9-24.5% with significantly increased light aromatic hydrocarbons. While iron in Fe/CC-n was finely dispersed on the charcoal, it occurred in Fe/CC-s as agglomerates. Mechanistic studies suggested that the volatile matter interacted with the charcoal forming a relatively stable intermediate, through which the hydrodeoxygenation and hydrogenation reactions took place more effectively. The strong catalytic activity of Fe/CC-n led to an extensive breakage of the volatile components and an effective hydrogenation of the fragments into CH4, while the moderate catalytic activity of Fe/CC-s allowed a selective hydrodeoxygenation of the intermediate to form upgraded bio-oil.