The use of alcohol as a fuel for internal combustion engines, either alone or in combination with other fuels, has been given much attention mostly because of its possible environmental and long-term economical advantages over fossil fuels.
Both ethanol and methanol have been considered for this purpose. While both may be obtained from petroleum or natural gas, ethanol is the most interesting since it is a renewable resource, easily obtained from organic material such as grain or sugarcane.
Fuel alcohols can be produced from a variety of crops, such as sugarcane, sugar beets, maize, barley, potatoes, cassava, sunflower, eucalyptus, etc. Two countries have developed significant bio-alcohol programmes: Brazil (ethanol from sugarcane) and Russia (methanol from eucalyptus). Alcohol can also be obtained synthetically, via ethene or acetylene, from calcium carbide, coal, oil gas, and other sources.
Agricultural alcohol for fuel requires substantial amounts of cultivable land with fertile soils and water. It is hardly an option for densely occupied and industrialized regions like Western Europe. For example, even if Germany were to be entirely covered with sugarcane plantations, it would get only half of its present energy needs (including fuel and electricity).
A mixture containing gasoline with at least 10% ethanol is known as gasohol. One common gasohol variant is "E15", containing 15% ethanol and 85% gasoline. These concentrations are generally safe for regular automobile engines, and some regions and municipalities mandate that the locally-sold fuels contain limited amounts of ethanol.
The term "E85 ethanol" is used for a mixture of 15% gasoline and 85% ethanol. Beginning with the model year 1999, a number of vehicles in the U.S. were manufactured so as to be able to run on E85 fuel without modification. Most of the vehicles have been officially classified as light trucks (a class containing minivans, SUVss, and pickup trucks). These vehicles are often labeled dual fuel or flexible fuel vehicles, since they can automatically detect the type of fuel and change the engine\'s behavior to compensate for the different ways that they burn in the engine cylinders.
In Brazil and the United States, the use of ethanol from sugar cane and grain as car fuel has been promoted by government programs. Some individual U.S. states in the corn belt began subsidizing ethanol from corn (maize) after the Arab oil embargo of 1973. The Energy Tax Act of 1978 authorized an excise tax exemption for biofuels, chiefly gasohol. The excise tax exemption alone has been estimated as worth US$11.4 billion per year. Another U.S. federal program guaranteed loans for the construction of ethanol plants, and in 1986 the U.S. even gave ethanol producers free corn.
Methanol too has been considered as a fuel, mainly in combination with gasoline. It has received less attention than ethanol, however, because it has a number of problems of its own. Its main advantage is that it can be easily manufactured from methane (the chief constituent of natural gas) as well as by pyrolysis of many organic materials. Pure methanol has been used in indy cars since the mid-1960's.
However, unlike ethanol, it is a toxic product; extensive exposure to it could lead to permanent health damage, including blindness. US maximum allowed exposure in air (40 h/week) are 1900 mg/m³ for ethanol, 900 mg/m³ for gasoline, and 260 mg/m³ for methanol. It is also quite volatile and therefore would increase the risk of fires and explosions.
Nevertheless, a drive to add a significant percentage of methanol to gasoline got very close to implementation in Brazil. A pilot experiment that was to be conducted in São Paulo was vetoed at the last minute by the city's mayor, out of concern for the health of gas station workers (who are mostly illiterate and could not be trusted to follow safety precautions).
The idea has not been heard of since.
There is an emerging view that current consumers of fossil fuels should move to using hydrogen as a fuel, creating a new so-called hydrogen economy. However, hydrogen should not be considered to be a fuel source in and of itself. In this view of energy usage, hydrogen is merely an intermediate energy storage medium existing between an energy source (be it solar power, biofuels, and even fossil fuels) and the place where the energy will be used. Because hydrogen in its gaseous state takes up a very large volume when compared to other fuels, logistics becomes a very difficult problem. One possible solution is to use ethanol to transport the hydrogen, then liberate the hydrogen from its associated carbon in a hydrogen reformer and feed the hydrogen into a fuel cell. Alternatively, some fuel cells can be directly fed by ethanol.
In early 2004, researchers at the University of Minnesota announced that they had invented a simple ethanol reactor that would take ethanol, feed it through a stack of catalysts, and output hydrogen suitable for a fuel cell. The device uses a rhodium-cerium catalyst for the initial reaction, which occurs at a temperature of about 700°C. This initial reaction mixes ethanol, water vapor, and oxygen and produces good quantities of hydrogen. Unfortunately, it also results in the formation of carbon monoxide, a substance that "chokes" most fuel cells and must be passed through another catalyst to be converted into carbon dioxide. The ultimate products of the simple device are roughly 50% hydrogen gas and 30% nitrogen, with the remaining 20% mostly composed of carbon dioxide. Both the nitrogen and carbon dioxide are fairly inert when the mixture is pumped into an appropriate fuel cell. Once the carbon dioxide is released back into the atmosphere, it is reabsorbed by plant life.
In the 1980s, Brazil seriously considered producing ethanol from cassava, a major food crop with massive starchy roots. However yields were lower than sugarcane, and the processing of cassava was considerably more complex, as it would require cooking the root to turn the starch into fermentable sugar. The babaçu plant was also investigated as a possible source of alcohol.
There is also growing interest in the use of biomass as a source for ethanol and other types of fuel. This is a broad-ranging idea, using various types of organic matter including purpose-grown crops of plants and trees as well as leftover waste products — even including animal waste.
At this time, most of the different processes for converting biomass into ethanol and other fuels are very complicated and not particularly efficient. A few processes have seen increasing buzz, including thermal depolymerization (though that process produces what is described as light crude oil).
Switching to a system with negative fuel energy balance would only increase the consumption of non-alcohol fuels. Such a system would only be worth considering as a way of exploiting non-alcohol fuels that may not
be suitable for transportation use, such as coal, natural gas, or biofuel from crop residues. (Indeed, many U.S proposals assume the use of natural gas for distillation.) However, many of the expected environmental and sustainability advantages of alcohol fuels would not be realized in a system with negative fuel balance.
Even a positive but small energy balance would be problematic: if the net fuel energy balance is 50%, then, in order to eliminate the use of non-alcohol fuels, it would be necessary to produce two gallons of alcohol for each gallon of alcohol delivered to the consumer.
In this regard, geography is the decisive factor. In tropical regions with abundant water and land resources, such as Brazil, the viability of production of ethanol from sugarcane is no longer in question; in fact, the burning of sugarcane residues (bagasse) generates far more energy than needed to operate the ethanol plants, and many of them are now selling electric energy to the utilities. Also, in countries with abundant hydroelectric power, the net fuel energy balance of the cycle could be improved to some extent by using electricity in the production, e.g. for milling and distillation.
The picture is quite different for other regions, such as the United States, where the climate is too cool for sugarcane. In the U.S., agricultural ethanol is generally obtained from grain, chiefly
maize, and the net fuel energy balance of that route is still critical.
However, continuous refinements to ethanol production procedures have much improved the benefit/cost ratio, and most studies of modern systems indicate that they now have a positive net energy balance.
Many other studies of corn ethanol production have been conducted, with greatly varied net energy estimates. Most indicate that production requires energy equvialent to 1/2, 2/3, or more of the fuel produced is required to run the process. A 2002 report by the United States Department of Agriculture concluded that corn ethanol production in the U.S. has a net energy value of 1.34, meaning 34% more energy was produced than what went in. This means that 75% (1/1.34) of each unit produced is required to replace the energy used in production. MSU Ethanol Energy Balance Study: Michigan State University, May 2002. This comprehensive, independent study funded by MSU shows that there is 56% more energy in a gallon of ethanol than it takes to produce it.
There has been concern about increased evaporative smog-forming hydrocarbon emissions. For example, the conservative organization RPPI claims that "adding ethanol to gasoline will at best have no effect on air quality and could even make it worse. Studies show ethanol could even increase emissions of nitrogen oxides and volatile organic compounds, which are major ingredients of smog." [1] Other critics have argued that the beneficial effects of ethanol can be achieved with other cheaper additives made from petroleum.
It is important to distinguish the issues. Ethanol in a blend with gasoline replaces tetra ethyl lead, benzene and MTBE -- all of which are additives that are meant to raise octane levesl. Ethanol, with an octane rating of 110, far surpasses regular gasoline and precludes any need for other additives that are dangerous. However, ethanol can increase vapor pressure of gasoline causing increased evaporative emissions which, on balance, are far less serious than lead, benzene or MTBE.
Ethanol as a straight fuel is far cleaner than gasoline in its own right and this has been recognized from the dawn of the automotive age. See, for instance, Kovarik's "Fuel of the Future" http://www.radford.edu/~wkovarik/lead
Needless to say, this advantage will be accrued only with agricultural ethanol, not with ethanol derived from petroleum — which, due to its much smaller cost, presently accounts for most of the alcohol produced for industrial consumption. This point must be taken into account when estimating the cost of the switch.
A somewhat related (but more compelling) argument is that developed regions like the United States and Europe consume much more fossil fuels than they can extract from their territory. Those countries have therefore become dependent on foreign suppliers, and their economies have thus become hostage to inernational events. The dependency has also been a major cause of wars, coups d'etat, and attendant misery and human rights violations. Thus switching to an agricultural ethanol economy, by lessening that dependency, would stabilize the economies of consumer countries, and make the world a better place for all.
Tax Incentives for ethanol and petroleum: U.S. General Accounting Office, September 2000. This study examines subsidies given to the oil industry and to the ethanol industry and finds that the amounts of those to the oil industry are far higher. See Statism.
In Brazil, ethanol is produced from sugar cane which is a more efficient source of fermentable carbohydrates than corn as well as much easier to grow and process. Brazil has the largest sugarcane crop in the world, which, besides ethanol, also yields sugar, electricity, and industrial heating. Sugar cane growing requires little labor, and government tax and pricing policies have made ethanol production a very lucrative business for big farms. As a consequence, over the last 25 years sugarcane has become one of the main crops grown in the country.
One ton (1,000 kg) of harvested sugarcane, as shipped to the processing plant, contains about 145 kg of dry fiber (bagasse) and 138 kg of sucrose. Of that, 112 kg can be extracted as sugar, leaving 23 kg in low-valued molasses. If the cane is processed for alcohol, all the sucrose is used, yielding 72 liters of ethanol. Burning the bagasse produces heat for distillation and drying, and (through lo Source | Copyright
