The water temperature was one factor that could affect the properties of pyrolytic
lignin. In this study, both cold (4 oC) water, following the method of B. Scholze and D.
Meier [10], and room-temperature distilled water was used as extraction media. Table 1
shows the properties of pyrolytic lignin extracted with different water temperatures. For
this part of the study, the water:bio-oil ratio was set at 5:1 by volume and the stirring
time was fixed at 2 h. The results indicated that the water temperatures did not
significantly affect the pyrolytic lignin’s properties. Therefore, the room-temperature
method, which saves the energy required to produce cold water, should be considered.
Method B was chosen over Method A, due to the time saving; however, the
acidity of the pyrolytic lignin from method B was still higher than that from method A.
In this part of the study, the amount of water used in Method B was investigated, with the hope that more water can remove more polar compounds including acids. Water:biooil
ratios of 5:1, 10:1, 15:1 and 20:1 by volume were studied. The amount of water was
fixed, while the bio-oil was varied in order to limit the total volume of liquid in the
extraction system, which used a constant stirring speed.
Figure 3 shows the properties of pyrolytic lignin (yield, acidity, C/H atomic ratio
and heating value) extracted with different water:bio-oil ratios. As shown in Figure 3A,
higher water:bio-oil ratios resulted in lower yields of pyrolytic lignin, indicating that
more polar-compounds in bio-oil dissolved into the aqueous phase. This loss of some light-phase compounds caused the decease in the acidity of the pyrolytic lignin, as show
in the Figure 3. The acidity decreased with the increasing water:bio-oil ratios from 5:1
to 15:1, then converged around 13 mg KOH/g oil.