Future Fuels
407
be considered as a very promising substrate for biohydrogen production.
The maximum theoretical hydrogen yield is 4 moles per mole of utilized
carbohydrates, expressed as glucose equivalents when carbohydrates are
used as substrates (Nandi and Sengupta 1998). Sweet sorghum stalks are
rich in sugars, mainly in sucrose that amounts up to 55% of dry matter and
in glucose (3.2% of dry matter). They also contain cellulose (12.4%) and hemicelluloses (10.2%; Billa et al. 1997). Sweet sorghum biomass is rich in readily
fermentable sugars and thus it can be considered as an excellent raw material
for fermentative hydrogen production.
13.5.2.4 Applications
Biohydrogen has properties similar to that of conventional hydrogen.
• Hydrogen, a colorless and odorless gas, is a clean fuel suitable for
automobiles at normal atmospheric conditions.
• Hydrogen can be stored in metal hydrates and compressed gas cylinders for vehicle application purposes.
• It is stable and coexists harmlessly with free oxygen until an input of
energy drives the exothermic (heat releasing) reaction.
• Fuel cells use hydrogen as a fuel that converts the chemical energy
contained in the hydrogen molecule into electrical energy.
13.5.3 Fischer–Tropsch Diesel
Synthetic fuels are often referred to as Fischer–Tropsch (F–T)diesel fuel or
gas-to-liquid fuel. The F–T process was named after the two German scientists who developed it in the 1920s—Frans Fischer and Hans Tropsch. The
Fischer-Tropsch process (F–T process) is the synthesis of long-chain hydrocarbons from CO and H 2 gas mixtures using a metal catalyst. Natural gas
is the major feedstock for the F–T process; the production comes under the
gas-to-liquid conversion process. F–T synthesis using coal is referred to as
the indirect liquefaction of coal. F–T manufactured from fossil fuels brings
no distinct greenhouse gas benefits in comparison with petroleum products.
A greenhouse benefit can only be achieved when F–T fuels are produced
from biomass.
Cleaning of synthesis gas is required before F–T processing and the process yields mixtures of different hydrocarbons. H 2 S removal is necessary
to protect synthesis catalysts as well as limit SO 2 emissions. In order to
maintain the catalyst for the maximum lifetime, sulfur levels in syngases
entering the synthesis reactor must be below 1 ppm by volume. These levels
are achieved through one of two methods—physical absorption by organic
fluids or chemical reactions between amines and sulfur compounds. The
cleaning synthesis process includes removal of tar, dust separation in the
407
be considered as a very promising substrate for biohydrogen production.
The maximum theoretical hydrogen yield is 4 moles per mole of utilized
carbohydrates, expressed as glucose equivalents when carbohydrates are
used as substrates (Nandi and Sengupta 1998). Sweet sorghum stalks are
rich in sugars, mainly in sucrose that amounts up to 55% of dry matter and
in glucose (3.2% of dry matter). They also contain cellulose (12.4%) and hemicelluloses (10.2%; Billa et al. 1997). Sweet sorghum biomass is rich in readily
fermentable sugars and thus it can be considered as an excellent raw material
for fermentative hydrogen production.
13.5.2.4 Applications
Biohydrogen has properties similar to that of conventional hydrogen.
• Hydrogen, a colorless and odorless gas, is a clean fuel suitable for
automobiles at normal atmospheric conditions.
• Hydrogen can be stored in metal hydrates and compressed gas cylinders for vehicle application purposes.
• It is stable and coexists harmlessly with free oxygen until an input of
energy drives the exothermic (heat releasing) reaction.
• Fuel cells use hydrogen as a fuel that converts the chemical energy
contained in the hydrogen molecule into electrical energy.
13.5.3 Fischer–Tropsch Diesel
Synthetic fuels are often referred to as Fischer–Tropsch (F–T)diesel fuel or
gas-to-liquid fuel. The F–T process was named after the two German scientists who developed it in the 1920s—Frans Fischer and Hans Tropsch. The
Fischer-Tropsch process (F–T process) is the synthesis of long-chain hydrocarbons from CO and H 2 gas mixtures using a metal catalyst. Natural gas
is the major feedstock for the F–T process; the production comes under the
gas-to-liquid conversion process. F–T synthesis using coal is referred to as
the indirect liquefaction of coal. F–T manufactured from fossil fuels brings
no distinct greenhouse gas benefits in comparison with petroleum products.
A greenhouse benefit can only be achieved when F–T fuels are produced
from biomass.
Cleaning of synthesis gas is required before F–T processing and the process yields mixtures of different hydrocarbons. H 2 S removal is necessary
to protect synthesis catalysts as well as limit SO 2 emissions. In order to
maintain the catalyst for the maximum lifetime, sulfur levels in syngases
entering the synthesis reactor must be below 1 ppm by volume. These levels
are achieved through one of two methods—physical absorption by organic
fluids or chemical reactions between amines and sulfur compounds. The
cleaning synthesis process includes removal of tar, dust separation in the