Atmospheric Hydrodeoxygenation of Biomass Fast Pyrolysis Vapor by MoO3

MoO3 has been tested as a catalyst in hydrodeoxygenation (HDO) of both model compounds (acetone and guaiacol) and real biomass pyrolysis vapors under atmospheric pressure. The pyrolysis vapor was obtained by fast pyrolysis of wood or lignin in a continuous fast pyrolysis reactor at a fixed temperature of 500 °C, and it subsequently passed through a downstream, close coupled, fixed bed reactor containing the MoO3 catalyst.

The influences of the catalyst temperature and the concentration of H2 on the HDO of the pyrolysis vapors were investigated. The level of HDO of the biomass pyrolysis vapors was not significant at temperatures below 400 °C. At 450 °C catalyst temperature and 93 vol % H2 concentration, the wood pyrolysis vapor was more active toward cracking forming gas species instead of performing the desired HDO forming hydrocarbons. The lignin pyrolysis vapor was more resistant to cracking and yielded 16.2 wt %daf organic liquid, while achieving 52% degree of deoxygenation at 450 °C catalyst temperature under 89 vol % H2 concentration.

The corresponding energy recovery in the liquid phase was 23.5%. The spent catalyst showed two deactivation routes, coke formation and reduction of MoO3 to MoO2, which is inactive in HDO. The catalyst experienced severe reduction at temperatures higher than 400 °C. The yields of coke relative to the fed biomass were in the range of 3–4 wt %daf for lignin and 5–6 wt %daf for wood. Compared to untreated bio-oil the upgraded lignin organic liquid showed improved compatibility with hydrocarbons and was miscible with a toluene/heptane mixture.