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Water for Energy and Fuel Production
In general, 60%–84% of the biomass carbon remains in the hydrochar. The char
composition is mainly affected by the nature of the feedstock, the temperature, and
the reaction time. For all feedstock, an increase in temperature increases the carbon
content and decreases the oxygen content of the hydrochar.
Hydrochar is often used for soil application as a fertilizer or a carbon sequester.
Some discussion in this regard is given by Libra et al. [15] and others [30–40].
Experimental evidences indicate that depending on the nature of char, it can remain
in soil for a long period. While less aromatic hydrochar stays longer in soils than
uncarbonized carbon, it decomposes faster than the char from dry pyrolysis. The
oxidation and degradation of char can be affected by the swelling–shrinking of clay
materials by the weather. The degradation of hydrochar is also accelerated by labile
carbon substrates and white-rot fungi, which are dominant char decomposers. In
general, the degradation and stability of hydrochar in top soils of Earth’s surface
can be affected by surface erosion and dissolution as dissolved organic carbon or
transported to subsoil as small particles with rain water. The char particles that are
imbedded in subsoil surface are less susceptible to erosion and degradation.
Hydrochar promotes the fungal growth and soil aggregation [15,30–40]. It will
very likely reduce the tensile strength, increase the hydraulic conductivity, and
enhance the soil water holding capacity (WHC). Hydrochar does not have a very
large internal surface area that may affect the penetration by water and nutrients
and the resulting microbial activity. While the WHC of hydrochar is generally
higher than that of mineral soils, it can be considerably reduced after it is fully
dried. Hydrochars are more acidic than biochars and they do undergo aging process
that can change the functional groups and therefore its effectiveness as nutrient. The
hydrochar can also be used as (1) activated carbon adsorbents, (2) raw materials
for the generation of nanostructured materials, (3) catalyst supports or as catalysts,
(4) CO 2 sorption materials, and (5) energy production and storage materials. These
applications of hydrochar are described in more detail in an excellent review by
Libra et al. [15].
The HTC process is accompanied by a large number of intermediate products
due to complex reaction mechanism. The solids coming out of the HTC process
represent the agglomerates of chemical substances. An elemental analysis of the
hydrochar shows that it may approach lignite or even sub-bituminous coal depending
on the reaction severity (Figure 5.2). An exception is resin whose H/C ratio remains
unaffected by the HTC process. As mentioned earlier, HTC coal from lignin tends to
have a lower hydrogen content, whereas coal from cellulose tends to achieve higher
carbon content [15,18,19,21].
HTC coal (hydrochar) is soluble in benzol–alcohol mixtures, alkaline solutions,
and ammonia [15]. The skeletal of HTC coal is very similar to that of natural coal,
although it exhibits a higher amount of functional groups compared to natural
bituminous coal. The removal of hydroxyl and carboxyl groups during the HTC
process makes HTC coal with a lower hydrophobicity than the original materials
[15,18,19,21]. While the inorganics largely remain in HTC coal, their relation with
process conditions is not well known. While HTC coal has a small surface area, this
area can be increased significantly (by 2 orders of magnitude) by removing extractables or by thermal treatment [15]. Observations of the nanostructure of HTC coal
Water for Energy and Fuel Production
In general, 60%–84% of the biomass carbon remains in the hydrochar. The char
composition is mainly affected by the nature of the feedstock, the temperature, and
the reaction time. For all feedstock, an increase in temperature increases the carbon
content and decreases the oxygen content of the hydrochar.
Hydrochar is often used for soil application as a fertilizer or a carbon sequester.
Some discussion in this regard is given by Libra et al. [15] and others [30–40].
Experimental evidences indicate that depending on the nature of char, it can remain
in soil for a long period. While less aromatic hydrochar stays longer in soils than
uncarbonized carbon, it decomposes faster than the char from dry pyrolysis. The
oxidation and degradation of char can be affected by the swelling–shrinking of clay
materials by the weather. The degradation of hydrochar is also accelerated by labile
carbon substrates and white-rot fungi, which are dominant char decomposers. In
general, the degradation and stability of hydrochar in top soils of Earth’s surface
can be affected by surface erosion and dissolution as dissolved organic carbon or
transported to subsoil as small particles with rain water. The char particles that are
imbedded in subsoil surface are less susceptible to erosion and degradation.
Hydrochar promotes the fungal growth and soil aggregation [15,30–40]. It will
very likely reduce the tensile strength, increase the hydraulic conductivity, and
enhance the soil water holding capacity (WHC). Hydrochar does not have a very
large internal surface area that may affect the penetration by water and nutrients
and the resulting microbial activity. While the WHC of hydrochar is generally
higher than that of mineral soils, it can be considerably reduced after it is fully
dried. Hydrochars are more acidic than biochars and they do undergo aging process
that can change the functional groups and therefore its effectiveness as nutrient. The
hydrochar can also be used as (1) activated carbon adsorbents, (2) raw materials
for the generation of nanostructured materials, (3) catalyst supports or as catalysts,
(4) CO 2 sorption materials, and (5) energy production and storage materials. These
applications of hydrochar are described in more detail in an excellent review by
Libra et al. [15].
The HTC process is accompanied by a large number of intermediate products
due to complex reaction mechanism. The solids coming out of the HTC process
represent the agglomerates of chemical substances. An elemental analysis of the
hydrochar shows that it may approach lignite or even sub-bituminous coal depending
on the reaction severity (Figure 5.2). An exception is resin whose H/C ratio remains
unaffected by the HTC process. As mentioned earlier, HTC coal from lignin tends to
have a lower hydrogen content, whereas coal from cellulose tends to achieve higher
carbon content [15,18,19,21].
HTC coal (hydrochar) is soluble in benzol–alcohol mixtures, alkaline solutions,
and ammonia [15]. The skeletal of HTC coal is very similar to that of natural coal,
although it exhibits a higher amount of functional groups compared to natural
bituminous coal. The removal of hydroxyl and carboxyl groups during the HTC
process makes HTC coal with a lower hydrophobicity than the original materials
[15,18,19,21]. While the inorganics largely remain in HTC coal, their relation with
process conditions is not well known. While HTC coal has a small surface area, this
area can be increased significantly (by 2 orders of magnitude) by removing extractables or by thermal treatment [15]. Observations of the nanostructure of HTC coal