396
Alternative Fuels for Transportation
refer to biomass-to-liquid (BTL) technologies, namely, biological conversion; that is, cellulosic ethanol and thermochemical conversion that includes
Fischer–Tropsch fuel, methanol, dimethyl ether (DME), and biohydrogen,
and so on.
These technologies are in the development stage and have yet to be
commercialized. The goal of second-generation biofuel processes is to extend
the amount of biofuel that can be produced sustainably by using biomass
consisting of the residual nonfood parts of current crops as well as other
crops not used for food purposes. These includes stems, leaves, and husks
that are left behind once the food crop has been extracted from the current
crops and other nonfood crops such as switch grass and jatropha, and also
industry waste such as wood chips, skins, and pulp. There are varieties of
conversion methods to produce second-generation biofuels from lignocelluloses. However, two commonly followed pathways are as follows:
• Biological method: Enzymes and other microorganisms are used
to convert cellulose and hemicellulose components of feedstocks to
sugars prior to their fermentation to produce ethanol
1. Bioethanol (cellulose, sorghum, cassava)
• Thermochemical method: Pyrolysis/gasification technologies produce a synthesis gas (CO + H 2 ) from which a wide range of longcarbon chain biofuels can be
requirements of:
1. Fischer–Tropsch liquids
2. Biohydrogen
3. Dimethyl ether
obtained and are reformed to the
Thermal conversion processes convert all biomass feedstocks into useful
energy forms and have a high degree of feedstock flexibility. In the biological
conversion process, only a limited fraction of biomass can be converted with
the known enzymatic technology to date. Biological processes may require
limited feedstock flexibility and hence microorganisms must be tailored to
the feedstock. Further research and development are needed to improve the
conversion rate and economics.
13.4 Biological Conversion
13.4.1 Bioethanol
Ethanol is an alternative that can be blended with gasoline to improve the
octane number and also for energy conservation reasons. Ethanol is a high
Alternative Fuels for Transportation
refer to biomass-to-liquid (BTL) technologies, namely, biological conversion; that is, cellulosic ethanol and thermochemical conversion that includes
Fischer–Tropsch fuel, methanol, dimethyl ether (DME), and biohydrogen,
and so on.
These technologies are in the development stage and have yet to be
commercialized. The goal of second-generation biofuel processes is to extend
the amount of biofuel that can be produced sustainably by using biomass
consisting of the residual nonfood parts of current crops as well as other
crops not used for food purposes. These includes stems, leaves, and husks
that are left behind once the food crop has been extracted from the current
crops and other nonfood crops such as switch grass and jatropha, and also
industry waste such as wood chips, skins, and pulp. There are varieties of
conversion methods to produce second-generation biofuels from lignocelluloses. However, two commonly followed pathways are as follows:
• Biological method: Enzymes and other microorganisms are used
to convert cellulose and hemicellulose components of feedstocks to
sugars prior to their fermentation to produce ethanol
1. Bioethanol (cellulose, sorghum, cassava)
• Thermochemical method: Pyrolysis/gasification technologies produce a synthesis gas (CO + H 2 ) from which a wide range of longcarbon chain biofuels can be
requirements of:
1. Fischer–Tropsch liquids
2. Biohydrogen
3. Dimethyl ether
obtained and are reformed to the
Thermal conversion processes convert all biomass feedstocks into useful
energy forms and have a high degree of feedstock flexibility. In the biological
conversion process, only a limited fraction of biomass can be converted with
the known enzymatic technology to date. Biological processes may require
limited feedstock flexibility and hence microorganisms must be tailored to
the feedstock. Further research and development are needed to improve the
conversion rate and economics.
13.4 Biological Conversion
13.4.1 Bioethanol
Ethanol is an alternative that can be blended with gasoline to improve the
octane number and also for energy conservation reasons. Ethanol is a high