The intense temperatures and pressures in ③ can be used for liquefaction or
molecular weight reduction of proteins and other polymer compounds. For algae,
polysaccharide saccharification can reportedly be achieved as well. This approach,
however, poses difficulties in terms of treatment of large volumes of algae due to
capacity issues with the internal pressure vessels (Huang et al. 2011).
B. Saccharification
Saccharification includes processes of acid hydrolysis, degradation under high
temperature and pressure, and enzymolysis. Acid hydrolysis may be achieved
through treatment with 3% sulfuric acid for 60 min at 120 °C. Most polysaccharides can be broken down to monosugars through acid hydrolysis, but monosugar
retention may also be reduced by excessive degradation. Too much breakdown
reduces the recovery rate for monosugars, which in turns lowers the recovery rate
for ethanol. It is also necessary to remove the sulfuric acid following hydrolysis.
Alkali neutralization offers a simple means of removing the sulfuric acid, but this
results in the formation of basis that can affect the growth and fermentation of yeast
and other microorganisms that participate in ethanol fermentation.
An alternative approach is to treat the decomposition solution with ion-exchange
resin to isolate the monosugars and sulfuric acid. Once recovered, the sulfuric acid
can be reused, but measures must also be taken to prevent corrosion of the device
by the acid, which increases the investment cost.
When treated at various pressures and temperatures, algae transform into algal
tissues or components, making monosugar extraction easier or causing decomposition. Land biomass such as lumber is broken down to emit its components under
supercritical conditions (temperature of 374 °C or greater, pressure of 22 MPa or
greater) or subcritical conditions (close to supercritical; see Fig. 9.1). Treatment of
algae with high pressures at supercritical or subcritical conditions (e.g., 500–
1000 Mpa at 60–80 °C for 30 min) results in liquefaction and saccharification taking
place simultaneously. This method cannot be used for the processing of large amounts
of algae, as it requires a pressure vessel capable of withstanding ultra-high pressure.
With enzyme-based saccharification, the type of enzyme used depends on the
components and bonding methods of the algal sugar. Algae polysaccharides contain
various constituent sugars, and the component monosugars and bonding methods
are varied (Table 9.1).
In the case of polysaccharides consisting of D-glucose, such as fibrin with is Dglucose beta-1,4 bond, fibrinogenase may be used for saccharification. For laminaran and other polysaccharides with a D-glucose b-1,3 bond, b-1,3 glucanase can
be used. The fibrinogenase XP-425 has been developed as an enzyme capable of
breaking down various kinds of bonds, including glucose b-1,4 and b-1,3 bonds
and bonds between xylose, and can be used for a broad range of liquefaction and
saccharification.
Just as substances have freezing (melting) points and evaporation (condensation)
points, so most also have a triple point and critical point. The critical point is a
characteristic of the substance; each substance has a different one. “Critical point”
9.2 Producing Ethanol with Algae
301
molecular weight reduction of proteins and other polymer compounds. For algae,
polysaccharide saccharification can reportedly be achieved as well. This approach,
however, poses difficulties in terms of treatment of large volumes of algae due to
capacity issues with the internal pressure vessels (Huang et al. 2011).
B. Saccharification
Saccharification includes processes of acid hydrolysis, degradation under high
temperature and pressure, and enzymolysis. Acid hydrolysis may be achieved
through treatment with 3% sulfuric acid for 60 min at 120 °C. Most polysaccharides can be broken down to monosugars through acid hydrolysis, but monosugar
retention may also be reduced by excessive degradation. Too much breakdown
reduces the recovery rate for monosugars, which in turns lowers the recovery rate
for ethanol. It is also necessary to remove the sulfuric acid following hydrolysis.
Alkali neutralization offers a simple means of removing the sulfuric acid, but this
results in the formation of basis that can affect the growth and fermentation of yeast
and other microorganisms that participate in ethanol fermentation.
An alternative approach is to treat the decomposition solution with ion-exchange
resin to isolate the monosugars and sulfuric acid. Once recovered, the sulfuric acid
can be reused, but measures must also be taken to prevent corrosion of the device
by the acid, which increases the investment cost.
When treated at various pressures and temperatures, algae transform into algal
tissues or components, making monosugar extraction easier or causing decomposition. Land biomass such as lumber is broken down to emit its components under
supercritical conditions (temperature of 374 °C or greater, pressure of 22 MPa or
greater) or subcritical conditions (close to supercritical; see Fig. 9.1). Treatment of
algae with high pressures at supercritical or subcritical conditions (e.g., 500–
1000 Mpa at 60–80 °C for 30 min) results in liquefaction and saccharification taking
place simultaneously. This method cannot be used for the processing of large amounts
of algae, as it requires a pressure vessel capable of withstanding ultra-high pressure.
With enzyme-based saccharification, the type of enzyme used depends on the
components and bonding methods of the algal sugar. Algae polysaccharides contain
various constituent sugars, and the component monosugars and bonding methods
are varied (Table 9.1).
In the case of polysaccharides consisting of D-glucose, such as fibrin with is Dglucose beta-1,4 bond, fibrinogenase may be used for saccharification. For laminaran and other polysaccharides with a D-glucose b-1,3 bond, b-1,3 glucanase can
be used. The fibrinogenase XP-425 has been developed as an enzyme capable of
breaking down various kinds of bonds, including glucose b-1,4 and b-1,3 bonds
and bonds between xylose, and can be used for a broad range of liquefaction and
saccharification.
Just as substances have freezing (melting) points and evaporation (condensation)
points, so most also have a triple point and critical point. The critical point is a
characteristic of the substance; each substance has a different one. “Critical point”
9.2 Producing Ethanol with Algae
301