Ethanol is alcohol by another name. There is more than one kind of alcohol, but ethanol is the kind humans drink. To make it, vintners ferment grapes, and vodka makers ferment and distill potatoes or grain. Fermentation may have been the first chemical reaction humans learned to control, a process they probably discovered when their food spoiled.
When a certain species of yeast, saccharomyces cerevisiae, attacks the sugars in fruit or processed grain in the absence of oxygen, it produces alcohol and carbon dioxide. This reaction brings us fine wine, modern fuel, and the convict’s pruno.
To produce alcohol from starchy ingredients, the starches must first be converted to sugars. In beer-making the grain is allowed to sprout in order to convert the starch. In industrial production of ethanol, the grain or other material may be treated with an enzyme or dilute acid.
To make pruno, the curious can follow the recipe given by the inmate Jarvis Masters in the poem found at the link below. Essentially the brewer uses a starter culture of yeast left over from the last batch. He adds this to a mash of fruit and water in a plastic bag, having learned from experiment how sweet to make his mixture and how much starter to use. He heats the mixture, to get the yeast started, and then wraps it to conserve heat and hides it away until the yeast has converted the mash to alcohol, sometimes adding sugar along the way to feed the yeast.
Commercial ethanol producers are taking advantage of the same chemical reaction, but in a more sophisticated way. They commonly use one of two procedures to convert corn into alcohol, wet milling or dry milling. These processes differ mainly in the initial treatment of the grain.
In dry milling, the corn is first ground in a hammermill. Water is added to make a mash. Enzymes are added to the mash to convert the starch to sugar. Ammonia is added for pH control, and to feed the yeast. The mash is cooked to reduce bacteria levels and then cooled, and then the yeast is added. Fermentation takes 40 to 50 hours, during which time the mixture is kept cool and agitated to provide the best conditions for the yeast. The resulting “beer” is removed to distillation columns, where the alcohol is removed from the stillage, which becomes livestock feed. The remaining alcohol and water mix is then conventionally distilled to about 190 proof by heating and condensing: alcohol evaporates at 170 degrees and water at 212 so the mixture is heated to 170 which drives off the alcohol. The fumes are then recaptured and condensed. Then the alcohol is separated from the remaining water it contains in a molecular sieve, which takes advantage of the different sizes of the alcohol and water molecules. The pure alcohol is then denatured, by adding about 5% natural gasoline, so that it avoids the tax on drinkable alcohol. It is ready to ship.
Wet milling is a similar process, but the grain is first soaked in water and sulfurous acid for up to 48 hours. It is then separated into its component parts, most of which are removed for other uses, such as the manufacture of corn oil and food stock. The starch may then be converted to ethanol by what are essentially the same processes as used in dry milling.
Cellulose is the most common organic material in the world. Converting it to ethanol is a more complicated process, but could be more a more reasonable choice than the destruction of food to make fuel. This kind of ethanol was actually made in Germany and the U.S. during WWI. In this process, wood or straw is first pretreated to free the cellulose from the lignin and the crystalline structure in which it is bound. There are different ways to do this, and all have disadvantages, with Ammonia Fiber Expansion the current leading contender for most effective process.
After pretreatment, the long cellulose molecules are broken up so that yeast can ferment their sugars. This breaking up, hydrolysis, is accomplished by using enzymes or acids. Acids work, but may produce undesirable byproducts, and must be separated from the mash after they have done their work. Enzymes are the way cows and other ruminants digest cellulose, and they can be used in industry as well. Many researchers are exploring ways to break down cellulose.
Fermentation may be accomplished with yeast, as in the production of ethanol from corn. There are also bacteria that can change sugars to alcohol, and their use is being studied. This process may yet bring useful results.
As of now, according to Nobel Prize winner Paul Crutzen, who led a study of the effects of liquid fuel production from biomass, the net effect of ethanol production by current methods is to increase global warming. He finds that producing ethanol leads to lessened global warming when the fuel is used, but manufacturing releases nitrous oxide, a gas that contributes to global warming, when the fuel is produced. In short, we need better methods, at least, and conservation while we await them. So leave the car in the garage, stay home, and maybe sip a little ethanol.
http://www.freejarvis.org/text/recipe.html
http://www.ethanolrfa.org/resource/made/
http://www.ethanolrfa.org/resource/cellulosic/
http://www.iogen.ca/cellulosic_ethanol/what_is_ethanol/process.html
http://www.futurepundit.com/archives/004610.html
