Biofuel (if cultivated, then also called agrofuel or agrifuel) can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from, recently dead biological material, most commonly plants. The fact that the material is only recently dead distinguishes biofuel from fossil fuel, which is derived from long dead biological material.
Theoretically, biofuel can be produced from any (biological) carbon source. The most common source by far is photosynthetic plants that capture solar energy. Many different plants and plant-derived materials are used for biofuel manufacture.
Biofuels are used globally, and biofuel industries are expanding in Europe, Asia, and the Americas. The most common use for biofuels is as liquid fuels for automotive transport. The use of renewable biofuels provides increased independence from petroleum and enhances energy security.
There are various current issues with biofuel production and use, which are being discussed in the popular media and scientific journals. These include the effect of moderating oil prices, the "food versus fuel" debate, carbon emissions levels, sustainable biofuel production, deforestation and soil erosion, impact on water resources, human rights issues, poverty reduction potential, biofuel prices, energy balance and efficiency, and centralized versus decentralized production models.
One of the greatest technical challenges is to develop ways to convert biomass energy specifically to liquid fuels for transportation. The two most common strategies for achieving this conversion are as follows:
- To grow sugar crops (sugar cane, sugar beet, and sweet sorghum), or starch (corn), and then use yeast fermentation to produce ethanol (ethyl alcohol)
- To grow plants that (naturally) produce oils, such as oil palm, soybean, algae, or jatropha. When these oils are heated, their viscosity is reduced, and they can be burned directly in a diesel engine, or the oils can be chemically processed to produce fuels such as biodiesel.
Wood and its byproducts can be converted into biofuels such as woodgas, methanol, or ethanol fuel. Some researchers are working to improve these processes.
Sugar cane can be used as a biofuel or food.
Biomass
Biomass is material derived from recently living organisms. Biomass can include plants, animals, and their by-products. For example, manure, garden waste, and crop residues are all sources of biomass. Unlike other natural resources such as petroleum, coal, and nuclear fuels, biomass is a renewable energy source based on the carbon cycle.
Animal waste is a persistent and unavoidable pollutant produced primarily by the animals housed in industrial-sized farms. Researchers from Washington University have figured out a way to turn manure into biomass. In April 2008, with the help of imaging technology, they noticed that vigorous mixing helps microorganisms turn farm waste into alternative energy, providing farmers with a simple way to treat their waste and convert it into energy.
There are also agricultural products specifically grown for biofuel production: corn, switchgrass, and soybeans, primarily in the United States; rapeseed, wheat, and sugar beet, primarily in Europe; sugar cane in Brazil; palm oil and miscanthus in Southeast Asia; sorghum and cassava in China; and jatropha in India. Hemp has also been proven to work as a biofuel. Biodegradable outputs from industry, agriculture, forestry, and households can be used for biofuel production, either using anaerobic digestion to produce biogas or using second generation biofuels; examples include straw, timber, manure, rice husks, sewage, and food waste. The use of biomass fuels can therefore contribute to waste management as well as energy security, and can help to prevent climate change, though alone they are not a comprehensive solution to these problems.
Bioenergy from Waste
Using waste biomass to produce energy can reduce the use of fossil fuels, reduce greenhouse gas emissions, and reduce pollution and waste management problems. A recent publication by the European Union highlighted the potential for waste-derived bioenergy to contribute to the reduction of global warming. The report concluded that 19 million tons of oil equivalent could be available from biomass by 2020, and that 46% of that would be from biowastes—municipal solid waste (MSW), agricultural residues, farm waste, and other biodegradable waste streams.
Landfill sites generate gases as the waste buried in them undergoes anaerobic digestion. These gases are known collectively as landfill gas (LFG). This gas can be burned and is considered a source of renewable energy, even though landfill disposals are often nonsustainable. Landfill gas can be burned either directly for heat or to generate electricity for public consumption. Landfill gas contains approximately 50% methane, the same gas that is found in natural gas.
Biomass can come from waste plant material. If landfill gas is not harvested, it escapes into the atmosphere: Allowing the landfill gas to go into the atmoshpere is not desirable because methane is a greenhouse gas, with more global warming potential than carbon dioxide. Over a time span of 100 years, methane has a global warming potential of 23 relative to CO2. That is, during this time, one ton of methane produces the same greenhouse gas (GHG) effect as 23 tons of CO2. When methane burns, the formula is CH4 + 2O2 = CO2 + 2H2O. Therefore, when landfill gas is harvested and burned, its global warming potential is reduced a factor of 23.
Frank Keppler and Thomas Rockmann discovered that living plants also produce methane CH4. The amount of methane produced by living plants is 10 to 100 times greater than that produced by dead plants (in an aerobic environment) but does not increase global warming because of the carbon cycle. Anaerobic digestion can be used as a distinct waste management strategy to reduce the amount of waste sent to landfill and to generate methane, or biogas. Any form of biomass can be used in anaerobic digestion and will break down to produce methane, which can be harvested and burned to generate heat or power.
A 3 MW landfill power plant would power 1,900 homes. It would eliminate 6,000 tons per year of methane from getting into the environment. It would eliminate 18,000 tons per year of CO2 from fossil fuel replacement. The effect would be the same as removing 25,000 cars from the road, or planting 36,000 acres (146 km2) of forest, or not using 305,000 barrels (48,500 m3) of oil per year.
Liquid Fuels for Transportation
Most transportation fuels are liquids, because vehicles usually require high energy density, as occurs in liquids and solids. Vehicles usually need high power density, which can be provided most inexpensively by an internal combustion engine. These engines require clean-burning fuels in order to keep the engine clean and minimize air pollution. The fuels that are easier to burn cleanly are typically liquids and gases. Only liquids meet the requirements of being both portable and clean burning. Also, liquids can be pumped, which means handling is easily mechanized, and thus less laborious.
First-Generation Biofuels
First-generation biofuels are biofuels made from sugar, starch, vegetable oil, or animal fats using conventional technology. The basic feedstocks for the production of first generation biofuels are often seeds or grains, such as wheat , which yields starch that is fermented into bioethanol, or sunflower seeds, which are pressed to yield vegetable oil that can be used in biodiesel. These feedstocks could also enter the animal or human food chain, and as the global population has risen their use in producing biofuels has been criticized since it diverts food away from the human food chain, leading to food shortages and rising food prices.
The most common first-generation biofuels are listed below.
- Vegetable oil
- Biodiesel
- Bioalcohols
- BioGas
- Solid Biofuels
- Syngas
Second-Generation Biofuels
Supporters of biofuels claim that a more viable solution is to increase political and industrial support for, and rapidity of, second-generation biofuel implementation from nonfood crops, including cellulosic biofuels. Second-generation biofuel production processes can use a variety of nonfood crops. These include waste biomass, the stalks of wheat, corn, wood, and special-energy-or-biomass crops (e.g., Miscanthus). Second-generation biofuels use biomass-to-liquid technology, including cellulosic biofuels from nonfood crops. Many second-generation biofuels are currently under development: biohydrogen, biomethanol, DMF, Bio-DME, Fischer-Tropsch diesel, biohydrogen diesel, mixed alcohols, and wood diesel.
Cellulosic ethanol production uses nonfood crops or inedible waste products and does not divert food away from the animal or human food chain. Lignocellulose is the "woody" structural material of plants. This feedstock is abundant and diverse, and in some cases (for example, citrus peels or sawdust) it is a significant disposal problem.
Producing ethanol from cellulose is a difficult technical problem to solve. In nature, ruminant livestock (such as cattle) eat grass and then use slow enzymatic digestive processes to break it into glucose (sugar). In cellulosic ethanol laboratories, various experimental processes are being developed to do the same thing; the sugars that are released can then be fermented to make ethanol fuel.
Third-Generation Biofuels
Algae fuel, also called oilgae or third-generation biofuel, is a biofuel from algae.
Second- and third-generation biofuels are also called advanced biofuels.
Fourth-Generation Biofuels
An emerging fourth generation of biofuels is based in the conversion of vegoil and biodiesel into gasoline. Craig Venter's company Synthetic Genomics is genetically engineering microorganisms to produce fuel directly from carbon dioxide on an industrial scale.
External Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Biofuel."
