Direct liquefaction of sawdust under syngas with and without catalyst

Sawdust loaded with 1 wt.% Mo catalyst was liquefied in a 250 ml autoclave at 300 °C, initial gas pressure of 2.0 MPa and reaction time of 30 min in attempt to produce more liquid fuels. The effects of different catalyst preparation methods including mechanical mixing, impregnation and ultrasonic treatment with or without solvents on liquefaction were compared. The effect of atmosphere and temperature was also examined. The results show that the highest yield of oil and lowest yield of preasphaltene and asphaltene are obtained using the sample loaded catalyst with ultrasonic treatment than those with impregnation or mechanical mixing no matter with or without solvents due to the well dispersion of the catalyst. Solvent, especially a hydrogen-donor, plays an important role in sawdust liquefaction, while gaseous hydrogen itself displays less action in promoting hydrogenation reaction and enhancing catalyst ability. Gaseous hydrogen and catalyst do show significant functions in the presence of solvent. Higher temperature is favorable of thermal decomposition, hydrogenation and hydrocracking reactions. Based on the experimental results, a two-step liquefaction mechanism is proposed.