Alcohol fuel

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Gasoline on the left, alcohol on the right at a filling station in Brazil

Rising energy prices and environmental problems have led to increased interest in alcohol as a fuel. Alcohol has been used as a fuel in other points in history but fossil fuels have become the dominant energy resource for the modern world. Much attention has been placed on the prospects of using ethanol as fuel for cars.

The first four aliphatic alcohols (methanol, ethanol, propanol, and butanol) are of interest as fuels because they can be synthesized biologically, and they have characteristics which allow them to be used in current engines. One advantage shared by all four alcohols is octane rating. Biobutanol has the additional attraction that its energy per kilogram is closer to gasoline than the other alcohols (while still retaining over 25% higher octane rating).

Alcohol fuels are usually of biological rather than petroleum sources. When obtained from biological sources, they are sometimes known as bioalcohols (e.g. bioethanol). It is important to note that there is no chemical difference between biologically produced alcohols and that obtained from other sources. However, ethanol that is derived from petroleum should not be considered safe for consumption as this alcohol contains about 5% methanol and may cause blindness or death. This mixture may also not be purified by simple distillation, as it forms an azeotropic mixture.

Bioalcohols are not used in most industrial processes, as alcohols derived from petroleum are usually cheaper in the current economic millieu. Many economists argue that this fact illustrates the economic infeasibility of using bioalcohol as a petroleum substitute and argue that government programs that mandate the use of bioalcohol are simply agricultural subsidies. ^{[citation needed]} Lines of counter-argument point out that estimations of feasibility assume the current, status quo infrastructure, which already exists, and therefore is not an initial cost.^{[citation needed]}

Recent "full up" energy analyses have shown that there is a net energy loss for use of bioalcohols. Use of more optimized crops, elimination of pesticides and fertilizers based on petroleum, and a more rigorous accounting process will help improve the feasibility of bioalcohols as fuels. ^{[citation needed]} The "full up" energy analysis does not include the energetic cost of synthesizing crude oil, making the comparison a largely moot point. This merely illustrates that extracting pre-made fuel requires less input energy than producing the fuel from other (potentially renewable) sources of energy.

Brazil is by far the largest producer of Alcohol Fuel in the world. They typically ferment Ethanol from sugarcane and sugar beets.

1 Methanol and ethanol
2 Propanol and Butanol
3 See also
4 External links

[edit] Methanol and ethanol

For more details on this topic, see Methanol fuel.

For more details on this topic, see Ethanol fuel.

Methanol and Ethanol both have advantages and disadvantages over fossil fuels, such as petrol and diesel. For instance, ethanol can run at a much higher compression ratio without octane-boosting additives (its octane rating is 129 as opposed to approximately 91 for ordinary petrol). It burns more completely because ethanol molecules contain oxygen; carbon monoxide emissions are 100% lower than fossil-fuelled engines because the only products of an ethanol combustion reaction are carbon dioxide, water, and heat.

However, ethanol is degrading to some plastic or rubber parts of fuel delivery systems designed to use petrol, and has 37% less energy per litre than petrol. Methanol is even more corrosive and its energy per liter is 55% lower than that of petrol. High compression ratios and corrosion-resistant materials can overcome these issues, but require extensive engine modification.

Methanol has also been proposed as a fuel of the future. There has been extensive use of methanol fuel in Funny Cars for years, and it has been the fuel of Indy car racing in North America since 1965.

Ethanol is already being used extensively as a fuel additive, and the use of ethanol fuel alone or as part of a mix with gasoline is increasing. In 2007, the Indy Racing League will use ethanol as its exclusive fuel, after 40 years of using methanol [1].

[edit] Propanol and Butanol

Propanol and butanol are considerably less toxic and less volatile than methanol. In particular, butanol has a high flashpoint of 35 °C, which is a benefit for fire safety, but may be a difficulty for starting engines in cold weather. The concept of flash point is however not directly applicable to engines as the compression of the air in the cylinder means that the temperature is several hundred degrees Celsius before ignition takes place.

The fermentation processes to produce propanol and butanol from cellulose are fairly tricky to execute, and the Weizmann organism (Clostridium acetobutylicum) currently used to perform these conversions produces an extremely unpleasant smell, and this must be taken into consideration when designing and locating a fermentation plant. This organism also dies when the butanol content of whatever it is fermenting rises to 7%. For comparison, yeast dies when the ethanol content of its feedstock hits 14%. Specialized strains can tolerate even greater ethanol concentrations - so-called turbo yeast can withstand up to 16% ethanol [2].

Despite these drawbacks, DuPont, British Petroleum, and British Sugar Corporation have reportedly started to convert an ethanol plant in the United Kingdom to produce butanol fuel from sugar beets (and in the future perhaps other starting materials).[3]