High Yields of Bio Oils from Hydrothermal Processing of Thin Black Liquor without the Use of Catalysts or Capping Agents

The mass yield of carbon from black liquor to bio-oil can be up to 80 wt.%.

“The mass yield of carbon from black liquor to bio-oil can be up to 80 wt.% [58].”

Over that temperature range, the bio-oil yield increased from ca. 67 wt.% to a maximum of 78 wt.% (ca. 648 K), before falling back to ca. 60 wt.% at 693 K.

“Over that temperature range, the bio-oil yield increased from ca. 67 wt.% to a maximum of 78 wt.% (ca.648 K), before falling back to ca. 60 wt.% at 693 K.”

In Orebom et al. [58], a maximum bio-oil yield of 76 wt.% was achieved at a residence time of 20 min, while the yield slightly decreased to ca. 68 wt.% when the experiment was extended up to 120 min.

“A maximum bio-oil yield of 76 wt.% was achieved at a residence time of 20 min while the yield slightly decreased to ca. 68 wt.% when the experiment was extended up to 120 min.”

In Orebom et al. [58], the char yield remained relatively stable at between 8 wt.% and 10 wt.% while the residence time ranged from 10 min to 120 min.

“The char yield remained relatively stable at between 8 wt.% and 10 wt.% while the residence time ranged from 10 min to 120 min (see Figure 11).”

The widely differing bio-oil yields of Orebom et al. [58] and Lee et al. [106] can be explained by the raw material used in the experiments, as well as the different expressions for the bio-oil yield and differences in the experimental set-ups.

“The widely differing bio-oil yields of Orebom et al. [58] and Lee et al. [106] can be explained by the raw material used in the experiments, as well as the different expressions for the bio-oil yield and differences in the experimental set-ups.”

In Orebom et al. [58], when the lignin concentration increased from 5 wt.% to 18 wt.%, the bio-oil yield decreased from around 73 wt.% to 58 wt.%, while the char yield increased from 8 wt.% to 40 wt.%.

“When the lignin concentration increased from 5 wt.% to 18 wt.%, the bio-oil yield decreased from around 73 wt.% to 58 wt.%, while the char yield increased from 8 wt.% to 40 wt.%.”

Orebom et al. studied the HTL of fresh, weak black liquor at a temperature of 613-693 K and a residence time of one hour in a batch reactor.

“Orebom et al. [58] studied the HTL of fresh, weak (low solid concentration) black liquor at a temperature of 613-693 K and a residence time of one hour in a batch reactor.”

They observed that the pH of the product decreased from 11 to 8-9 as the reaction temperature increased from 613 K to 683 K, whereby most of the phenols were transferred from the aqueous phase to bio-oil.

“They observed that the pH of the product decreased from 11 to 8-9 as the reaction temperature increased from 613 K to 683 K, whereby most of the phenols were transferred from the aqueous phase to bio-oil.”

Orebom et al. reported that in the liquefaction of black liquor, the yield of monocyclic aromatic compounds, such as phenols, cresols and mesitols, increased nearly linearly from 3 wt.% to 9 wt.% when the temperature increased from 613 K to 693 K.

“Orebom et al. [58] reported that in the liquefaction of black liquor, the yield of monocyclic aromatic compounds, such as phenols, cresols and mesitols, increased nearly linearly from 3 wt.% to 9 wt.% when the temperature increased from 613 K to 693 K.”

In Orebom et al. [58], adding an aliphatic alcohol (ethanol) reduced the char yield when the experiments were made with an initial lignin concentration of 18 wt.% and a residence time of 1 h.

“The authors noticed that adding an aliphatic alcohol (ethanol) reduced the char yield when the experiments were made with the initial lignin concentration of 18 wt.%and the residence time of 1 h.”

It was unclear whether Orebom et al. [58] diluted the lignin content by adding 10 wt.% of ethanol or kept the lignin content constant.

“However, it was unclear whether they diluted the lignin content by adding 10 wt.% of ethanol or the lignin content was kept constant.”

The absence of composition or HHV data for bio-oils obtained at different residence times in Orebom et al. [58] makes it impossible to estimate the effect of residence time on the energy recovery from feedstock to bio-oil.

“This makes it impossible to estimate the effect of residence time on the energy recovery from feedstock to bio-oil.”

In Orebom et al. [58], the yield of monomers was relatively stable, being 4 wt.% at 30 min and 5 wt.% at 60 min.

“The yield of monomers was also relatively stable, being 4 wt.% at 30 min and 5 wt.% at 60 min.”

In Orebom et al. [58], without ethanol the char yield was 27.5 wt.%, but it decreased significantly to 9.6 wt.% with an initial ethanol concentration of 10 wt.%.

“Without ethanol the char yield was 27.5 wt.% but it decreased significantly to 9.6 wt.% with an initial ethanol concentration of 10 wt.%.”

Orebom et al. [58] did not report any data on the composition or HHV for bio-oils obtained at different residence times.

“However, Orebom et al. [58] did not report any data on the composition or HHV for bio-oils obtained at different residence times.”

Orebom et al. reported that the Mw of feedstock Kraft lignin in black liquor was 3000 g/mol and the corresponding value of the bio-oil produced was about 550 g/mol.

“Orebom et al. [58] reported that the M w of feedstock (Kraft lignin in black liquor) was 3000 g/mol and the corresponding value of the bio-oil produced was ca.550 g/mol.”

In black liquor, inorganic sulfur compounds are present as anions, mainly bisulfide (HS-), sulfite (SO32-), sulfate (SO42-), and thiosulfate (S2O32-).

“The inorganic sulfur compounds are present as anions in the BL, mainly as bisulfide (HS–),36 sulfite (SO32–), sulfate (SO42–), and thiosulfate (S2O32–).”