Alcohol fuel

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

Rising energy prices and global warming have led to increased interest in alternative fuels. 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. Generally speaking, the chemical formula for alcohol fuel is C_nH_2n+2O. The larger n is, the higher the energy density.

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 advantage that its energy density 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 those 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 still in developmental and research stages. Use of optimized crops with higher yields of energy, elimination of pesticides and fertilizers based on petroleum, and a more rigorous accounting process will help improve the feasibility of bioalcohols as fuels.

1 Alcohol in Brazil
2 Methanol and ethanol
3 Propanol and Butanol
4 See also
5 External links

[edit] Alcohol in Brazil

Brazil is by far the largest producer of alcohol fuel in the world, typically fermenting ethanol from sugarcane and sugar beets. The country produces a total of 18 billion liters annually, of which 3.5 billion are exported, 2 billion of them to the US (Portuguese)[1]. Alcohol cars debuted in the Brazilian market in 1978 and became quite popular because of heavy subsidy, but in the 80's prices rose and gasoline regained the leading market share.

But from 2004 on, alcohol is rapidly rising it's market share once again because of new technologies involving hybrid fuel car engines [2], called "Flex" by all major car manufacturers (Volkswagen, General Motors, Fiat, etc.). "Flex" engines work with gasoline, alcohol or any mixture of both fuels. As of February 2007, approx. 80% of new vehicles sold in Brazil are hybrid fuel (Portuguese)[3].

Because of the Brazilian leading production and technology, many countries became very interested in importing alcohol fuel and adopting the "Flex" vehicle concept [4]. In March 7th of 2007, US president George W. Bush visited the city of São Paulo to sign agreements with Brazilian president Lula on importing alcohol and it's technology as an alternative fuel.

[edit] Methanol and ethanol

Ethanol used as a fuel.

Main articles: Methanol fuel, Ethanol fuel

Methanol and Ethanol both have advantages and disadvantages over fossil fuels, such as petrol and diesel. For instance, both alcohols can run at a much higher compression ratio without octane-boosting additives (its octane rating is 129 (RON), equal to 102 (MON) or 116 (AKI) as opposed to approximately 91 (RON), 81 (MON), 86 (AKI) for ordinary European petrol; note that American 'regular-grade gasoline' is about 1 point higher on all 3 scales, but still offers very similar performance.) Ethanol 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. Despite this reduction in carbon monoxide, ethanol releases as much or more carbon dioxide than its gasoline counterpart (though this carbon dioxide has previously been drawn from the air in biologically-produced ethanol, so there is no net modern release, as there is for fossil fuels). There are also lower NOx emissions, as ethanol needs more energy to vaporise than petrol - so it draws more heat out of the air in a cylinder than petrol, having a greater cooling effect, which reduces the opportunity for nitrogen and oxygen in the cylinder (as air) to fuse into poisonous nitrogen oxides.

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 used as a fuel for open wheel car racing in North America since 1965. Unfortunately, although its octane rating is comparable to ethanol and it has similar emissions, it is also toxic (producing some toxic emissions, formaldehyde and formic acid), and has a lower (-38%) energy content than ethanol (-55% compared to petrol.)

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 [5].

Methanol combustion is: 2CH₄O + 3O₂ → 2CO₂ + 4H₂O + heat

Ethanol combustion is: C₂H₆O + 3O₂ → 2CO₂ + 3H₂O + heat

[edit] Propanol and Butanol

Main article: Butanol fuel

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 [6]. However, if ordinary Saccharomyces yeast can be modified to improve its ethanol resistance, scientists may yet one day produce a strain of the Weizmann organism with a butanol resistance higher than the natural boundary of 7%. This would be useful because butanol has a higher energy density than ethanol, and because waste fibre left over from sugar crops used to make ethanol could be made into butanol, raising the alcohol yield of fuel crops without there being a need for more crops to be planted.

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).[7] Enerey Environment International developed a method for producing butanol from biomass, which involves the use of two separate micro-organisms in sequence to minimize production of acetone and ethanol byproducts.[8]

Propanol combustion is: 2C₃H₈O + 9O₂ → 6CO₂ + 8H₂O + heat

Butanol combustion is: C₄H₁₀O + 6O₂ → 4CO₂ + 5H₂O + 24kJ/mL