Upgrading of pyrolysis bio-oil using nickel phosphide catalysts

Abstract

Pyrolysis bio-oil is a promising source of liquid fuels, but requires upgrading to remove excess oxygen and produce a satisfactory fuel oil. Nickel phosphide has been shown to be an active composition for hydrodeoxygenation (HDO) of bio-oil model compounds. In this study, nickel phosphide catalysts were used for direct upgrading of an actual pyrolysis bio-oil derived from cedar chips. The activity of Ni2P deposited on an amorphous SiO2 support for HDO was first verified using the model compound, 2-methyltetrahydrofuran (2-MTHF), at the temperature of the pyrolysis oil treatment of 350°C. The Ni2P/SiO2 catalyst showed high activity for 2-MTHF hydrodeoxygenation under atmospheric pressure hydrogen with low cracking activity.Fast pyrolysis and catalytic upgrading were conducted sequentially using a laboratory-scale, two-stage system consisting of a fluidized bed pyrolyzer and a fluidized bed catalytic reactor both operating at 0.1MPa, with a hydrogen partial pressure of 0.06MPa. It was found that the Ni2P/SiO2 catalyst was moderately effective in upgrading the biomass pyrolysis vapors and producing a refined bio-oil with decreased oxygen content. The moderate deoxygenation of the bio-oil was confirmed by elemental analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Gas chromatography–mass spectrometry (GC–MS) analysis showed that the treated bio-oil mainly consisted of phenolic compounds, and the MS spectra before and after upgrading suggested that reactions including hydrodeoxygenation, hydrogenation, decarbonylation, and hydrolysis occurred during the upgrading. Furthermore, Ni2P supported on ZSM-5 zeolite eliminated oxygen in the bio-oil with smaller reduction in the oil yield than Ni2P supported on SiO2. The deoxygenation activity of the nickel phosphide catalysts was higher than that of conventional catalysts such as Ni/SiO2, Pd/C and an FCC-catalyst.