HHV MJ=kg
ð
Þ¼0:3491 C
ð Þ þ 1:1783 H
ð Þ þ 0:1005 S
ð Þ þ 0:1034 O
ð Þ
þ 0:0151 N
ð Þ þ 0:021 A
ð Þ
ð5Þ
O ¼ 100 À C þ H þ N þ S
ð
Þ
ð 6Þ
Energy Densification ED
ð Þ ¼ HHV Biochar or Biocrude
ð
Þ =HHV Biomass
ð7Þ
The elemental composition of the raw material, biochar, and biocrude obtained
from the hydrothermal carbonization and liquefaction process is given in Table 5.
The high heating value (HHV) of the hydrothermal products compared to the
feedstock is increased significantly due to the carbonization. It is observed from
Table 5 that the hydrothermal products (biochar and biocrude) have a high energy
densification ratio higher than 1, which proves the decarboxylation and deoxygenation reactions were involved during the hydrothermal carbonization and liquefaction. Table 6 shows the elemental composition of reference feedstock. Figure 7
depicts the van Krevelen plot, and it shows that the lignocellulosic feedstock is
converted to products similar to that of lignite and liquefaction of algal biomass
resulted in biocrude that resembles petroleum crude. The only disadvantage is the
high nitrogen content in the biocrude.
Compared to other energy intensification processes, the hydrothermal processes
have higher ratios and also low heat of reactions as the subcritical and supercritical
water lowers the activation energy. Additionally, the mechanical dewatering or any
other preheating is not required, as the feedstock of the process is moist biomass.
Hydrothermal coal is also called biocoal and has ash melting point similar to
lignite, although in the case of algal biomass, the minerals in the solid product fuse
together to form a sticky dense slurry-like material that changes the behavior of
biochar entirely compared to lignocellulosic biochar. The algal biochar and solid
residue are hygroscopic, and they are difficult to separate. Materials that are obtained
from hydrothermal carbonization also have shown promising properties with varying functionalities, morphologies, and porosities [60]. They have important applications in a variety of modern fields such as electrode materials in superior
performance supercapacitors, Na-based batteries, Li-ion batteries, and fuel cells [14].
At supercritical conditions, hydrogen and methane from biomass can also be
manufactured from single-step hydrothermal gasification process without the formation of any solid residue:
C 6 H 12 O 6 þ 6H 2 O ! 6CO 2 þ 14H 2
ð8Þ
C 6 H 12 O 6 ! 3CH 4 þ 3CO 2
ð9Þ
Thus, Table 7 shows promising results that both lignocellulosic and algal biomass
can be used for hydrogen gas production.
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
217
ð
Þ¼0:3491 C
ð Þ þ 1:1783 H
ð Þ þ 0:1005 S
ð Þ þ 0:1034 O
ð Þ
þ 0:0151 N
ð Þ þ 0:021 A
ð Þ
ð5Þ
O ¼ 100 À C þ H þ N þ S
ð
Þ
ð 6Þ
Energy Densification ED
ð Þ ¼ HHV Biochar or Biocrude
ð
Þ =HHV Biomass
ð7Þ
The elemental composition of the raw material, biochar, and biocrude obtained
from the hydrothermal carbonization and liquefaction process is given in Table 5.
The high heating value (HHV) of the hydrothermal products compared to the
feedstock is increased significantly due to the carbonization. It is observed from
Table 5 that the hydrothermal products (biochar and biocrude) have a high energy
densification ratio higher than 1, which proves the decarboxylation and deoxygenation reactions were involved during the hydrothermal carbonization and liquefaction. Table 6 shows the elemental composition of reference feedstock. Figure 7
depicts the van Krevelen plot, and it shows that the lignocellulosic feedstock is
converted to products similar to that of lignite and liquefaction of algal biomass
resulted in biocrude that resembles petroleum crude. The only disadvantage is the
high nitrogen content in the biocrude.
Compared to other energy intensification processes, the hydrothermal processes
have higher ratios and also low heat of reactions as the subcritical and supercritical
water lowers the activation energy. Additionally, the mechanical dewatering or any
other preheating is not required, as the feedstock of the process is moist biomass.
Hydrothermal coal is also called biocoal and has ash melting point similar to
lignite, although in the case of algal biomass, the minerals in the solid product fuse
together to form a sticky dense slurry-like material that changes the behavior of
biochar entirely compared to lignocellulosic biochar. The algal biochar and solid
residue are hygroscopic, and they are difficult to separate. Materials that are obtained
from hydrothermal carbonization also have shown promising properties with varying functionalities, morphologies, and porosities [60]. They have important applications in a variety of modern fields such as electrode materials in superior
performance supercapacitors, Na-based batteries, Li-ion batteries, and fuel cells [14].
At supercritical conditions, hydrogen and methane from biomass can also be
manufactured from single-step hydrothermal gasification process without the formation of any solid residue:
C 6 H 12 O 6 þ 6H 2 O ! 6CO 2 þ 14H 2
ð8Þ
C 6 H 12 O 6 ! 3CH 4 þ 3CO 2
ð9Þ
Thus, Table 7 shows promising results that both lignocellulosic and algal biomass
can be used for hydrogen gas production.
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
217