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Sugar cane can be used as a biofuel.

Biofuel (also called agrofuel) can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from biomass. This article, however, is principally about biofuel in the form of liquid or gas transportation fuel derived from biomass. Biomass can also be used directly for heating or power. One type of biomass is wood, which is frequently used in industry, either by itself to create energy or with other combustible matter (such as coal) to burn and create heat. (Wood has been burned for millennia - as solids.)

Biofuel is considered a means of reducing^[1] greenhouse gas emissions and increasing energy security by providing an alternative to fossil fuels. However, In October 2007, Nobel Laureate Paul Crutzen published findings that the release of Nitrous Oxide (N₂O) among the commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming than fossil fuel savings due to global cooling. Crops with less N demand, such as grasses and woody coppice species have more favourable climate impacts. ^[2]

Biofuels are used globally: biofuel industries are expanding in Europe, Asia and the Americas. The most common use for biofuels is in automotive transport (for example E10 fuel). Biofuel can be produced from any carbon source that can be replenished rapidly e.g. plants. Many different plants and plant-derived materials are used for biofuel manufacture.

[edit] Biomass

Main article: Biomass

Biomass is material derived from recently living organisms. This includes plants, animals and their by-products. For example, manure, garden waste and crop residues are all sources of biomass. It is a renewable energy source based on the carbon cycle, unlike other natural resources such as petroleum, coal, and nuclear fuels. Agricultural products specifically grown for biofuel production include 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 South-East 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 biofuel processes; 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 fuel security and help to prevent climate change, though alone they are not a comprehensive solution to these problems.

[edit] History

Humans have used biomass fuels - that is, solid biofuels - for heating and cooking since the discovery of fire. Following the discovery of electricity, it became possible to use biofuels to generate electrical power as well. However, the discovery and use of fossil fuels: coal, gas and oil, have dramatically reduced the amount of biomass fuel used in the developed world for transport, heat and power.

Liquid biofuels have been used since the early days of the car industry. Nikolaus August Otto, the German inventor of the internal combustion engine, conceived his invention to run on ethanol. Rudolf Diesel, the German inventor of the Diesel engine, designed it to run on peanut oil. Henry Ford originally designed the Ford Model T, a car produced from 1903 to 1926, to run completely on ethanol. However, when crude oil became cheaply available (thanks to oil reserves discovered in Pennsylvania and Texas), cars began using fuels derived from mineral oil: petroleum or diesel.

Nevertheless, before World War II, biofuels were seen as providing an alternative to imported oil. Germany powered its vehicles using a blend of gasoline with alcohol fermented from potatoes, called Reichskraftsprit. In Britain, grain alcohol was blended with petrol by the Distillers Company Limited under the name Discol and marketed through Esso's affiliate Cleveland.

After the war, cheap Middle Eastern oil lessened interest in biofuels. But the oil shocks of 1973 and 1979 increased interest from governments and academics. The counter-shock of 1996 again reduced oil prices and interest.

Since around 2000 renewed interest in biofuels has been seen. The drivers for biofuel use and development include rising oil prices, concerns over the potential oil peak, greenhouse gas emissions (global warming), rural development interests, and instability in the Middle East. The US president George W. Bush said in his 2006 State of the Union speech that the US should replace 75% of imported oil with biofuel by 2025.

The U.S. Dept. of Energy has earmarked $375 million to fund bioenergy research centers. Second generation biofuel production processes are in development (see below). These allow biofuel to be derived from any source of biomass, not just from food crops such as corn and soy beans.

Many U.S. Presidential candidates support biofuel development, in a recent debate Mike Huckabee said, "We once had a president who said, "Let's go to the moon in 10 years," and we were there in eight. And we did that when we started with a technology of bottle rockets when we got the thing launched. And we all saw that we can do it." ^[3] Several candidates from both parties have voiced similar support for energy independence.

[edit] Carbon emissions

Biofuels and other forms of renewable energy aim to be carbon neutral. This means that the carbon released during the use of the fuel, e.g. through burning to power transport or generate electricity, is reabsorbed and balanced by the carbon absorbed by new plant growth. These plants are then harvested to make the next batch of fuel. Carbon neutral fuels lead to no net increases in atmospheric carbon dioxide levels, which means that global warming need not get any worse.

In practice, biofuels are not carbon neutral. This is because energy is required to grow crops and process them into fuel. Examples of energy use during the production of biofuels include: fertilizer manufacture, fuel used to power machinery, and fuel used to transport crops and fuels to and from biofuel processing plants. The amount of fuel used during biofuel production has a large impact on the overall greenhouse gas emissions savings achieved by biofuels.

In October 2007, further doubt has been thrown on the advantages of biofuel by Nobel Laureate Paul Crutzen, who says that the advantages of reduced carbon dioxide emissions are more than offset by increased nitrous oxide emissions. . Nitrous oxide is both a potent greenhouse gas and a destroyer of atmospheric ozone.

The carbon emissions produced by biofuels are calculated using a technique called Life Cycle Analysis (LCA). This uses a "cradle to grave" or "well to wheels" approach to calculate the total amount of carbon dioxide and other greenhouse gases emitted during biofuel production, from putting seed in the ground to using the fuel in cars and trucks. Many different LCAs have been done for different biofuels, with widely differing results. The majority of LCA studies show that biofuels provide significant greenhouse gas emissions savings when compared to fossil fuels such as petroleum and diesel. Therefore, using biofuels to replace a proportion of the fossil fuels that are burned for transportation can reduce overall greenhouse gas emissions.

This does assume however that the land used for growing the crops would alternatively be desert or paved area. If the land was previously a (tropical rain-) forest, the carbon absorption of this forest should be deducted from the greenhouse gas savings. This implies that the net effect of burning bio-fuels is an increase in greenhouse gasses. This effect should be incorporated in the LCA, to get a proper overview of the total net effect. Using waste material from plantation forests on previous agricultural land could be carbon positive, due to the carbon stored below ground in the root systems.

The well-to-wheel analysis for biofuels has shown that first generation biofuels can save up to 60% carbon emission and second generation biofuels can save up to 80% as opposed to using fossil fuels.^[4] However these studies do not take into account emissions from nitrogen fixation, deforestation, land use, or any indirect emissions.

However, a 2007 study by scientists from Britain, U.S., Germany, Switzerland and including Professor Paul Crutzen, who won a Nobel Prize for his work on ozone, have reported that measurements of emissions from the burning of biofuels derived from rapeseed and corn have been found to produce more greenhouse gas emissions than they save.^[5]

The claim that biofuels result in emissions savings has also been critiqued on the grounds that it overlooks the 'displacement' effects of large-scale biofuel production, in terms of its direct and indirect role in promoting land use changes and soil carbon losses.^[6]

In 2006, a UK Government study showed that carbon emissions were reduced between 50% and 60%. This was when biofuels were used in conjunction with other fuels such as petrol and diesel.

[edit] 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 is available from biomass by 2020, 46% from bio-wastes: municipal solid waste (MSW), agricultural residues, farm waste and other biodegradable waste streams.^[7][8]

Landfill sites generate gases as the waste buried in them undergoes anaerobic digestion. These gases are known collectively as landfill gas: this can be burned and is a source of renewable energy. Landfill gas (LFG) can be burned either directly for heat or to generate electricity for public consumption. Landfill gas contains approximately 50 percent methane, the same gas that is found in natural gas.

If landfill gas is not harvested, it escapes into the atmosphere: this is not desirable because methane is a greenhouse gas, with more global warming potential than carbon dioxide. ^[9][10] Over a time span of 100 years, methane has a global warming potential of 23 relative to CO₂. ^[9] Therefore, 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. So by harvesting and burning landfill gas, its global warming potential is reduced a factor of 23, in addition to providing energy for heat and power.

PhD Frank Keppler and PhD Thomas Rockmann discovered that living plants also produce methane CH₄.^{[citation needed]} The amount of methane produced by living plants is 10 to 100 times greater than that produced by dead plants 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 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, power or to power certain automotive vehicles.

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. This is 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 of oil per year.

[edit] First generation biofuels

'First-generation fuels' refer to biofuels made from sugar, starch, vegetable oil, or animal fats using conventional technology.^[11]

The most common first generation biofuels are listed below.

[edit] Vegetable oil

Main article: Vegetable oil used as fuel

Vegetable oil can be used for either food or fuel; the quality of the oil may be lower for fuel use. Vegetable oil can be used in many older diesel engines (equipped with indirect injection systems), but only in warm climates. In most cases, vegetable oil is used to manufacture biodiesel, which is compatible with most diesel engines when blended with conventional diesel fuel. MAN B&W Diesel, Wartsila and Deutz AG offer engines that are compatible with straight vegetable oil. Used vegetable oil is increasingly being processed into biodiesel, and at a smaller scale, cleaned of water and particulates and used as a fuel.

[edit] Biodiesel

Main article: Biodiesel

Biodiesel is the most common biofuel in Europe. It is produced from oils or fats using transesterification and is a liquid similar in composition to mineral diesel. Its chemical name is fatty acid methyl (or ethyl) ester (FAME). Oils are mixed with sodium hydroxide and methanol (or ethanol) and the chemical reaction produces biodiesel (FAME) and glycerol. 1 part glycerol is produced for every 10 parts biodiesel.

Biodiesel can be used in any diesel engine when mixed with mineral diesel. In some countries manufacturers cover their diesel engines under warranty for 100% biodiesel use, although Volkswagen Germany, for example, asks drivers to make a telephone check with the VW environmental services department before switching to 100% biodiesel (see biodiesel use). Many people have run their vehicles on biodiesel without problems. However, the majority of vehicle manufacturers limit their recommendations to 15% biodiesel blended with mineral diesel. In many European countries, a 5% biodiesel blend is widely used and is available at thousands of gas stations [1][2].

In the USA, more than 80% of commercial trucks and city buses run on diesel. Therefore "the nascent U.S. market for biodiesel is growing at a staggering rate—from 25 million gallons per year in 2004 to 78 million gallons by the beginning of 2005. By the end of 2006 biodiesel production was estimated to increase fourfold to more than 1 billion gallons," energy expert Will Thurmond writes in an article for the July-August 2007 issue of THE FUTURIST magazine.

[edit] Bioalcohols

Main article: Alcohol fuel

Biologically produced alcohols, most commonly ethanol and less commonly propanol and butanol, are produced by the action of microorganisms and enzymes through fermentation.

[edit] Butanol

Main article: Butanol fuel

Biobutanol (also called biogasoline) is often claimed to provide a direct replacement for gasoline, because it can be used directly in a gasoline engine (in a similar way to biodiesel in diesel engines).

It is not in widespread production, and engine manufacturers have not made statements about its use^{[verification needed]}. While on paper (and a few lab tests) it appears that butanol has sufficiently similar characteristics with gasoline such that it should work without problem in any gasoline engine, no widespread experience exists. Butanol is formed by ABE fermentation (acetone, butanol, ethanol) and experimental modifications of the process show potentially high net energy gains with butanol as the only liquid product. Butanol will produce more energy and allegedly can be burned "straight" in existing gasoline engines (without modification to the engine or car) [3], and is less corrosive and less water soluble than ethanol, and could be distributed via existing infrastructures. DuPont and BP are working together to help develop Butanol.

[edit] Bioethanol

Main article: Ethanol fuel

Ethanol is the most common biofuel worldwide. This alcohol fuel is produced by fermentation of sugars derived from wheat, corn, sugar beet and sugar cane. The production methods used are enzymatic digestion (to release sugars from stored starches e.g. from wheat and corn), fermentation of the sugars, distillation and drying. Ethanol can be used in petrol engines as a replacement for gasoline; it can be mixed with gasoline to any percentage, see common ethanol fuel mixtures for information on ethanol. All petrol engines can run on blends of up to 15% bioethanol with petroleum/gasoline. For higher percentage blends, engine modifications are needed. Many car manufacturers are now producing flex-fuel vehicles, which can run on any combination of bioethanol and petrol, up to 100% bioethanol.

[edit] Biomethanol

Main article: methanol

Methanol is currently produced from natural gas, a fossil fuel. It can also be produced from biomass (biomethanol). The methanol economy is an interesting alternative to the hydrogen economy.

[edit] BioGas

Main article: biogas

Biogas is produced by the process of anaerobic digestion of organic material by anaerobes. It can be produced either from biodegradable waste materials or by the use of energy crops fed into anaerobic digesters to supplement gas yields. The solid byproduct, digestate, can be used as a biofuel or a fertiliser.

Biogas contains methane and can be recovered from industrial anaerobic digesters and mechanical biological treatment systems. Landfill gas is a less clean form of biogas which is produced in landfills through naturally occurring anaerobic digestion. If it escapes into the atmosphere it is a potent greenhouse gas.

Oils and gases can be produced from various biological wastes:

• Thermal depolymerization of waste can extract methane and other oils similar to petroleum.
• GreenFuel Technologies Corporation developed a patented bioreactor system that uses nontoxic photosynthetic algae to take in smokestacks flue gases and produce biofuels such as biodiesel, biogas and a dry fuel comparable to coal.^[12]

[edit] Solid Biofuels

Examples include wood, charcoal, and dried excrement.

[edit] Second generation biofuels

Main article: Second generation biofuels

Second generation biofuels use biomass to liquid technology, including cellulosic biofuels from non food crops. ^[13]

The following second generation biofuels are under development:

• BioHydrogen
• Bio-DME
• Biomethanol
• DMF
• HTU diesel
• Fischer-Tropsch diesel
• Mixed Alcohols (i.e., mixture of mostly ethanol, propanol and butanol, with some pentanol, hexanol, heptanol and octanol)

Bio-DME, Fischer-Tropsch, BioHydrogen diesel, Biomethanol and Mixed Alcohols all use syngas for production. This syngas is produced by gasification of biomass. HTU (High Temperature Upgrading) diesel is produced from particularly wet biomass stocks using high temperature and pressure to produce an oil.

BioHydrogen is the same as hydrogen except it is produced from a biomass feedstock. This is done using gasification of the biomass and then reforming the methane produced, or alternatively, this can be accomplished with some organisms that produce hydrogen directly under certain conditions. BioHydrogen can be used in fuel cells to produce electricity.

DMF. Recent advances in producing DMF from fructose and glucose using catalytic biomass-to-liquid process have increased its attractiveness.

Bio-DME is the same as DME but is produced from a bio-sources. Bio-DME can be produced from Biomethanol using catalytic dehydration or it can be produced from syngas using DME synthesis. DME can be used in the compression ignition engine.

Biomethanol is the same as methanol but it is produced from biomass. Biomethanol can be blended with petrol up to 10-20% without any infrastructure changes. ^[14]

HTU diesel is produced from wet biomass. It can be mixed with fossil diesel in any percentage without need for infrastructure. ^[15]

Fischer-Tropsch diesel (FT)diesel is produced using gas-to-liquids technology. FT diesel can be mixed with fossil diesel at any percentage without need for infrastructure change.

Mixed alcohols are produced from syngas with catalysts similar to those used for methanol. Most R&D in this area is concentrated in producing mostly ethanol. However, some fuels are marketed as mixed alcohols (see Ecalene) ^{[16] [17]}. Mixed alcohols are superior to pure methanol or ethanol, in that the higher alcohols have higher energy content. Also, when blending, the higher alcohols increase compatibility of gasoline and ethanol, which increases water tolerance and decreases evaporative emissions. In addition, higher alcohols have also lower heat of vaporization than ethanol, which is important for cold starts. (For another method for producing mixed alcohols from biomass see bioconversion of biomass to mixed alcohol fuels)

Wood diesel A new biofuel was developed by the University of Georgia from wood chips. The oil is extracted and then added to unmodified diesel engines. Either new plants are used or planted to replace the old plants. The charcoal byproduct is put back into the soil as a fertilizer. According to the director Tom Adams since carbon is put back into the soil, this biofuel can actually be carbon negative not just carbon neutral. Carbon negative decreases carbon dioxide in the air reversing the greenhouse effect not just reducing it