compound ethanol, also known as ethyl
alcohol or grain alcohol, is the
bio-alcohol found in alcoholic beverages. When non-chemists
refer to "alcohol", they almost always mean
ethanol. It is also increasingly being used as a fuel (usually
replacing or complementing gasoline). Ethanol's chemical formula
Pure ethanol is a flammable, colorless liquid with a boiling point of 78.5° C. Its low melting point of -114.5° C allows it to be used in antifreeze products. It has a pleasant odor reminiscent of whiskey. Its density is 789 g/l about 20% less than that of water. It is easily soluble in water and is itself a good solvent, used in perfumes, paints and tinctures. Alcoholic drinks have a large variety of tastes, since various flavor compounds are dissolved during brewing. >A solution of 70-85% of ethanol is commonly used as a disinfectant; it kills organisms by denaturing their proteins and dissolving their lipids: it is effective against most bacteria and fungi, and many viruses, but is ineffective against bacterial spores. This disinfectant property of ethanol is the reason that alcoholic beverages can be stored for a long time.
Ethanol can lose a proton from the hydroxyl group and is a very weak acid, weaker than water. The CAS number of ethanol is 64-17-5 and its UN number is UN 1170.
Ethanol as fuel
Ethanol is flammable and burns more cleanly than many other fuels. When fully combusted its combustion products are only carbon dioxide and water. For this reason, it is favoured for environmentally conscious transport schemes and has been used to fuel public buses. However, pure ethanol attacks certain rubber and plastic materials and cannot be used in unmodified car engines. Additionally, ethanol has a much higher octane rating than ordinary gasoline, requiring changes to the spark timing in engines.
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, SUVs, 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$1.4 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.
Arguments in favor of ethanol are the search for decreased dependency on oil producing countries and the decreased net ouptut of the greenhouse gas carbon dioxide. Some critics argue that it is mainly a government subsidy for corn-growing agribusiness. The Archer Daniels Midland Corporation of Decatur, Illinois, better known as ADM, the world's largest grain processor, produces 40% of the ethanol used to make gasohol in the U.S.. The company and its officers have been eloquent in their defense of ethanol and generous in contributing to both political parties.
Other critics contend that it is economically absurd to consider ethanol from grain as a replacement for petroleum, when industrial ethanol is made from petroleum feedstocks because it is far cheaper than fermented ethanol. Environmentalists do not like arguments like this, since they advocate a transition to renewable energy rather than continued usage of fossil fuels.
There is widespread belief that ethanol containing fuel is more environmentally friendly than gasoline without additives. However, there is a controversy over whether requiring ethanol in automotive fuel is wise since it has been argued that the beneficial effects of ethanol can be achieved with other cheaper additives made from petroleum. Also, both the Environmental Protection Agency and the National Academy of Sciences have issued "reports showing 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."
Net energy value
Some studies have found that the total energy needed to produce ethanol from grain—including fermentation, fertilizing, fuel for farm tractors, harvesting and transporting the grain, building and operating an ethanol plant, and the natural gas used to distill corn sugars into alcohol—exceeds the energy content of ethanol. Since production energy comes mostly from fossil fuels, gasohol isn't just wasting money but hastening the depletion of nonrenewable resources, critics have argued. Most such studies were based on data collected in the 1970s and early 1980s.
Early corn ethanol production systems were shown to have a negative net energy balance, meaning that the energy produced did not equal or exceed the amount of energy going in to make the ethanol. However, refinements to ethanol production procedures has turned the tide, and most studies of modern systems indicate that they now have a positive net energy balance. As late as 2001, analyses have continued to indicate that ethanol has a negative energy balance. A peer-reviewed study by Cornell University ecology professor David Pimentel pointed toward this conclusion, but the study was rebutted by others in the field, forcing Pimentel to revise his figures. In August 2003, he stated in a Cornell bulletin that production of ethanol only takes 29% more energy than it produces.
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 productin 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.
Sugar cane grows in the southern United States, but not in the cooler climates where corn is dominant. However, many regions that currently grow corn are also appropriate areas for growing sugar beets. Some studies indicate that using these sugar beets would be a much more efficient method for making ethanol in the U.S. than using corn.
The Brazilian experiment
Brazil, ethanol is produced from sugar cane—which is a more efficient source of fermentable carbohydrates than corn, and much easier to grow and process. Sugarcane 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.
The cane is pressed, fermented, and distilled at large ethanol plants, typically owned and run by big farms or farm consortia, and located near the producing fields. The stalk fibers (bagasse) which are left over from sugarcane processing are regularly used as fuel by the refineries, thus reducing the production costs. The bulk product is sold at regulated prices to the state oil company (Petrobrás).
Most cars run either on alcohol or on gasohol; only recently have dual-fuel engines become available. The market share of the two types has varied a lot over the last decades, in response to fuel price changes (which are fixed by the government, largely for political reasons). Most gas stations sell both fuels.
The Brazilian ethanol-for-fuel program significantly reduced the country's oil import bill, and noticeably improved the air quality in big cities. However, it also brought a host of environmental and social problems of its own. Sugarcane fields are traditionally burned just before harvest, in order to remove the leaves and kill snakes. Therefore, in sugarcane-growing parts of the country, the smoke from burning fields turns the sky gray throughout the harvesting season. As winds carry the smoke into nearby towns, air pollution goes critical and respiratory problems soar. Thus, the air pollution which was removed from big cities was merely transfered (and multiplied) to the rural areas. (This practice has been decreasing of late, due to pressure from the public and health authorities; but the powerful sugarcane growers' lobby has managed to prevent a total ban.)
The ethanol program also led to widespread replacement of small farms and varied agriculture by vast seas of sugarcane monoculture, leading to a decrease in biodiversity and further shrinkage of the residual native forests (not only from deforestation but also through fires caused by the burning of adjoining fields). The replacement of food crops by the more lucrative sugarcane has also led to a sharp increase in food prices over the last decade.
>Since sugarcane only requires hand labor at harvest time, this shift also created a large population of destitute migrant workers, who can only find temporary employment as cane cutters (at about US$3–5 per day) for one or two months every year. This huge social problem has contributed to political unrest and violence in rural areas, which are now plagued by recurrent farm invasions, vandalism, armed confrontations, and assassinations.
Ethanol in the hydrogen economy
An emerging view is that current consumers of fossil fuels should transition 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, producing 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, 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.
1- Ethanol Molecule Summary - PubChem
2- Ethanol CDC -- Occupational Safety and Health