there are many methods available, this chapter focuses on one of the fastest and costeffective conversion methods, which is hydrothermal conversion.
2 Hydrothermal Conversion
The biomass is converted into biochar, biocrude, and biogas in the presence of
subcritical or supercritical water at high temperatures and pressures. The three
phases of water and various points can be identified from the phase diagram as
given in Fig. 1. Water at subcritical conditions breaks the long chain macromolecules of the biomass into smaller fragments by acting as a catalyst due to its higher
ionic product that favors acids or base-catalyzed reactions [14]. In general, hydrothermal conversion is further divided into three separate processes: (1) hydrothermal
carbonization, (2) hydrothermal liquefaction, and (3) hydrothermal gasification
depending on the severity of its operating conditions.
Table 2 Lignocellulosic biomass feedstock composition
Category
Feedstock
Constituents (wt% in dry basis)
Cellulose
Hemicellulose
Lignin
Woody biomass
Pine wood
45.3
22.5
26.8
Oak wood
38.1
23
32
Spruce wood
45.6
20
28.2
Agricultural residue
Rice straw
41.1
23.8
19.5
Common reed
43.3
29.6
27.1
Corncob
38.8
33
13.1
Cotton cocoon shell
32.6
10.2
48.7
Table 3 Algal biomass feedstock composition
Category
Feedstock
Constituents (wt% in dry basis)
Protein Carbohydrate Lipids
Others (ash and
fibers)
Macroalgae Caulerpa serrulata
14.48
45.6
4.24
27.66
Daviesia divaricata
8.89
14.6
10.51 38.99
Padina tetrastromatica 3.87
15.54
3.92
34.58
Turbinaria triquetra
4.13
16.3
1.62
53.19
Sargassum
subrepandum
4.22
17.21
3.83
39.73
Microalgae Chaetoceros calcitrans 34
6.0
16
44
Nannochloropsis
oculata
35
7.8
18
39.2
Dunaliella tertiolecta
20
12.2
15
52.8
Chroomonas salina
29
9.1
12
49.9
Isochrysis galbana
29
12.9
23
35.1
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
205
2 Hydrothermal Conversion
The biomass is converted into biochar, biocrude, and biogas in the presence of
subcritical or supercritical water at high temperatures and pressures. The three
phases of water and various points can be identified from the phase diagram as
given in Fig. 1. Water at subcritical conditions breaks the long chain macromolecules of the biomass into smaller fragments by acting as a catalyst due to its higher
ionic product that favors acids or base-catalyzed reactions [14]. In general, hydrothermal conversion is further divided into three separate processes: (1) hydrothermal
carbonization, (2) hydrothermal liquefaction, and (3) hydrothermal gasification
depending on the severity of its operating conditions.
Table 2 Lignocellulosic biomass feedstock composition
Category
Feedstock
Constituents (wt% in dry basis)
Cellulose
Hemicellulose
Lignin
Woody biomass
Pine wood
45.3
22.5
26.8
Oak wood
38.1
23
32
Spruce wood
45.6
20
28.2
Agricultural residue
Rice straw
41.1
23.8
19.5
Common reed
43.3
29.6
27.1
Corncob
38.8
33
13.1
Cotton cocoon shell
32.6
10.2
48.7
Table 3 Algal biomass feedstock composition
Category
Feedstock
Constituents (wt% in dry basis)
Protein Carbohydrate Lipids
Others (ash and
fibers)
Macroalgae Caulerpa serrulata
14.48
45.6
4.24
27.66
Daviesia divaricata
8.89
14.6
10.51 38.99
Padina tetrastromatica 3.87
15.54
3.92
34.58
Turbinaria triquetra
4.13
16.3
1.62
53.19
Sargassum
subrepandum
4.22
17.21
3.83
39.73
Microalgae Chaetoceros calcitrans 34
6.0
16
44
Nannochloropsis
oculata
35
7.8
18
39.2
Dunaliella tertiolecta
20
12.2
15
52.8
Chroomonas salina
29
9.1
12
49.9
Isochrysis galbana
29
12.9
23
35.1
Hydrothermal Conversion of Biomass into Fuel and Fine Chemicals
205