Influence of the stirring duration were also investigated. The experiments were
done with a water:bio-oil ratio of 10:1 and water temperature of 30 °C. Figure 4 shows
the properties of pyrolytic lignin extracted with different stirring durations. The results
showed that the stirring time did not significantly affect the heating value or C/H atomic
ratio of the pyrolytic lignin. However, the acidity decreased with increasing stirring
duration from 0.5 to 1 h. After that, the acidity became quite stable, indicating that the
dissolving of polar compounds in the water was saturated. Thus, the stirring duration
should be at least 1 h , in order to effectively reduce the acidity.