Introduction:A variety of fuels can be made from biomass resources including the liquid fuels ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels such as hydrogen and methane.
Biofuels research and development is composed of three main areas: producing the fuels, applications and uses of the fuels, and distribution infrastructure.
Biofuels are primarily used to fuel vehicles, but can also fuel engines or fuel cells for electricity generation.
Ethanol is made by converting the carbohydrate portion of biomass into sugar, which is then converted into ethanol in a fermentation process similar to brewing beer.
Ethanol is the most widely used biofuel today with current capacity of 1.8 billion gallons per year based on starch crops such as corn.
Ethanol produced from cellulosic biomass is currently the subject of extensive research, development and demonstration efforts.
Biodiesel is produced through a process in which organically derived oils are combined with alcohol (ethanol or methanol) in the presence of a catalyst to form ethyl or methyl ester.
The biomass- derived ethyl or methyl esters can be blended with conventional diesel fuel or used as a neat fuel (100 percent biodiesel).
Biodiesel can be made from soybean or Canola (rapeseed) oils, animal fats, waste vegetable oils, or microalgae oils.
Biofuels from Synthesis Gas:
Biomass can be gasified to produce a synthesis gas composed primarily of hydrogen and carbon monoxide, also called syngas or biosyngas.
Hydrogen can be recovered from this syngas, or it can be catalytically converted to methanol.
It can also be converted using Fischer-Tropsch catalyst into a liquid stream with properties similar to diesel fuel, called Fischer-Tropsch diesel. However, all of these fuels can also be produced from natural gas using a similar process.
B. Conversion Processes:
Biochemical Conversion Processes:
Enzymes and microorganisms are frequently used as biocatalysts to convert biomass or biomass derived compounds into desirable products.
Cellulase and hemicellulase enzymes break down the carbohydrate fractions of biomass to five and six carbon sugars, a process known as hydrolysis.
Yeast and bacteria ferment the sugars into products such as ethanol. Biotechnology advances are expected to lead to dramatic biochemical conversion improvements.
Photobiological Conversion Processes:
Photobiological processes use the natural photosynthetic activity of organisms to produce biofuels directly from sunlight.
For example, the photosynthetic activities of bacteria and green algae have been used to produce hydrogen from water and sunlight.
Thermochemical Conversion Processes:
Heat energy and chemical catalysts are used to break down biomass into intermediate compounds or products.
In gasification, biomass is heated in an oxygen-starved environment to produce a gas composed primarily of hydrogen and carbon monoxide.
In pyrolysis, biomass is exposed to high temperatures in the absence of air, causing it to decompose. Solvents, acids and bases can be used to fractionate biomass into an array of products including sugars, cellulosic fibers and lignin.
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