Thus to reduce the solid residue and increase the yield of biocrude, the feedstock
chosen must be in such a way that its lignin content is carefully balanced with
cellulose and hemicellulose. The hydrothermal conversion of pure lignin at higher
temperatures of 350
C, carried out by Wahyudiono et al. [29], resulted in products
catechol, phenols, and cresols, which confirms the existence of secondary hydrolysis
of methoxy groups. Similar results were found for hydrothermal conversion of Kraft
pine resulting in major products as phenol, 4-ethylguaiacol, and methyl
dehydroabietate [30].
Conversion of Carbohydrates The carbohydrates in algae mainly constitute polysaccharides, celluloses, hemicelluloses, and starches. They are hydrolyzed to form
simple sugars with glucose as the main product; the glucose is then rapidly converted
to fructose which in turn degrades with fragmentation to form carbon-carbon double
bond components like aldehydes and phenols which are intermediates, thus
converting into gaseous products like H 2 , CO 2 , CH 4 , etc. [31].
Conversion of Proteins Proteins mostly consist of linear polymeric amino acids
that are connected to carboxylic and amine group using C-N bond links. During the
hydrothermal conversion process, these bonds get hydrolyzed to produce free amino
acids which quickly undergo decarboxylation and deamination to produce hydrocarbons, amines, aldehydes, and acids [32].
Conversion of Lipids Lipids are mainly comprised of fatty acid triglycerides
(TAG) which are nonpolar components with aliphatic characteristics. TAG is
hydrolyzed to form fatty acids and glycerol, where glycerol readily gets converted
into water-soluble components. Free fatty acids are pretty much stable but partially
get converted into hydrocarbons via decarboxylation [33].
3 Hydrothermal Conversion Process Conditions
The hydrothermal conversion processes depend upon various parameters: temperature and heating rate, solvent or hydrothermal media, biomass to solvent loading,
residence time, and catalysts. Once the reaction is over, the reaction products are
taken out and filtered for the residual water. Then it is washed with extraction solvent
to leach out the biocrude from the biochar, where the excess solvent is removed by
vacuum evaporation. There are various methods by which the recovery of the
products is calculated, and most widely used conventions are given below:
Biocrude yield wt%
ð
޼W es =W f  100
ð1Þ
Biogas yield wt%
ð
Þ¼W c À W rp =W c  100
ð2Þ
Biochar yield wt%
ð
޼ W r =W f  100
ð3Þ
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
209
chosen must be in such a way that its lignin content is carefully balanced with
cellulose and hemicellulose. The hydrothermal conversion of pure lignin at higher
temperatures of 350
C, carried out by Wahyudiono et al. [29], resulted in products
catechol, phenols, and cresols, which confirms the existence of secondary hydrolysis
of methoxy groups. Similar results were found for hydrothermal conversion of Kraft
pine resulting in major products as phenol, 4-ethylguaiacol, and methyl
dehydroabietate [30].
Conversion of Carbohydrates The carbohydrates in algae mainly constitute polysaccharides, celluloses, hemicelluloses, and starches. They are hydrolyzed to form
simple sugars with glucose as the main product; the glucose is then rapidly converted
to fructose which in turn degrades with fragmentation to form carbon-carbon double
bond components like aldehydes and phenols which are intermediates, thus
converting into gaseous products like H 2 , CO 2 , CH 4 , etc. [31].
Conversion of Proteins Proteins mostly consist of linear polymeric amino acids
that are connected to carboxylic and amine group using C-N bond links. During the
hydrothermal conversion process, these bonds get hydrolyzed to produce free amino
acids which quickly undergo decarboxylation and deamination to produce hydrocarbons, amines, aldehydes, and acids [32].
Conversion of Lipids Lipids are mainly comprised of fatty acid triglycerides
(TAG) which are nonpolar components with aliphatic characteristics. TAG is
hydrolyzed to form fatty acids and glycerol, where glycerol readily gets converted
into water-soluble components. Free fatty acids are pretty much stable but partially
get converted into hydrocarbons via decarboxylation [33].
3 Hydrothermal Conversion Process Conditions
The hydrothermal conversion processes depend upon various parameters: temperature and heating rate, solvent or hydrothermal media, biomass to solvent loading,
residence time, and catalysts. Once the reaction is over, the reaction products are
taken out and filtered for the residual water. Then it is washed with extraction solvent
to leach out the biocrude from the biochar, where the excess solvent is removed by
vacuum evaporation. There are various methods by which the recovery of the
products is calculated, and most widely used conventions are given below:
Biocrude yield wt%
ð
޼W es =W f  100
ð1Þ
Biogas yield wt%
ð
Þ¼W c À W rp =W c  100
ð2Þ
Biochar yield wt%
ð
޼ W r =W f  100
ð3Þ
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
209