Upgrading of the liquid fuel from fast pyrolysis of biomass over MoNi/γ-Al2O3 catalysts

The hydrotreatment of bio-oil, which obtained from fast pyrolysis of pine sawdust, was investigated over MoNi/γ-Al2O3 catalyst under mild conditions (373 K, 3 MPa hydrogen pressure). Acetic acid was taken as a model compound to investigate the effects of Mo promoter contents and reducing temperatures of catalysts on the catalysts activity under the condition of 473 K and 3 MPa hydrogen pressure. X-ray diffraction and temperature programmed reduction showed that the addition of Mo promoter benefited the uniformity of nickel species and inhibited the formation of NiAl2O4 spinel in the catalysts. The GC spectrum of liquid products showed the mechanism of the model reaction. The maximum conversion of acetic acid (33.20%) was attained over 0.06MoNi/γ-Al2O3 catalysts being reduced at 873 K. This catalyst was chosen for the upgrading of raw bio-oil. After the upgrading process, the pH value of the bio-oil increased from 2.33 to 2.77. The water content increased from 35.52 wt.% to 41.55 wt.% and the gross calorific value increased from 13.96 MJ/kg to 14.17 MJ/kg. The hydrogen content in the bio-oil increased from 6.25 wt.% to 6.95 wt.%. The product properties of the upgraded bio-oil, particularly the hydrogen content and the acidity were considerably improved. The results of gas chromatography–mass spectrometry analysis showed that both hydrotreatment and esterification had happened over 0.06MoNi/γ-Al2O3 (873) catalyst during the upgrading process.