Making Ethanol fuel
Ethanol has been used by humans for thousands of years, in part because it is easy to make. Ethanol can be produced from any biological feedstock’s that contain appreciable amounts of sugar or materials that can be converted into sugar such as starch or cellulose. Sugar beets and sugar
cane are examples of feedstock’s that contain sugar. Corn contains starch that can relatively easily be converted into sugar. A significant percentage of trees and grasses are made up of cellulose, which can also be converted to sugar, although with more difficulty than required to convert starch.
The process is shown in here in its simplest form:
- Wheat or corn kernels are ground in a hammermill to expose the starch.
- The ground grain is mixed with water, cooked briefly and enzymes are added to convert the starch to sugar using a chemical reaction called hydrolysis.
- Yeast is added to ferment the sugars to ethanol.
- The ethanol is separated from the mixture by distillation and the water is removed from the mixture using dehydration.
The ethanol production process starts by grinding up the feedstock so it is more easily and quickly processed in the following steps. Once ground up, the sugar is either dissolved out of the material or the starch or cellulose is converted into sugar. The sugar is then fed to microbes that use it for food, producing ethanol and carbon dioxide in the process. A final step purifies the ethanol to the desired concentration. Ethanol is also made from a wet-milling process. Many larger ethanol producers use this process, which also yields products such as high-fructose corn sweetener.
A new process is under development for making ethanol from the cellulose and hemicellulose components of less expensive biomass feedstock’s such as wood and agricultural residues. The method is similar to the traditional process that uses the starch component of grain or corn. However, this method is more difficult because these types of feedstock require more complex pretreatment and hydrolysis steps that use acid or enzymes before the sugars can be fermented to ethanol.
Fermentation is a biochemical process carried out by microscopic organisms called yeast. Yeast is commonly known as a major component in making bread. Bakers use the yeasts ability to make carbon dioxide gas to make the bread rise, making it thicker. If it were not for yeast, pizza dough would be flatter than a pancake. Yeast is anaerobic, meaning it can live and eat without needing oxygen. Many living things eat sugar, and yeast eats sugar too. When oxygen is limited, yeast consumes simple sugars, but is unable to absorb all of the available energy in sugar. During the partial absorption process while digesting the sugar, it is converted into ethanol and carbon dioxide gas. While Ethanol can also be made from the sugar found in most kitchens, it takes a lot of sugar to fill the tank of your car with ethanol. Some countries, such as Brazil, that grow a lot of sugar use it to make ethanol for cars. Brazil has been producing ethanol fuels for decades. The United States does not have enough sugar cane plants to do this, so the U.S. has focused on making
ethanol from corn.
Scientists have also invented ways to make ethanol synthetically, without utilizing nature’s help. The process converts a byproduct of making gasoline into ethanol. Although this process is used, more than 90% of the ethanol produced per year is made using yeast. Corn has less sugar in it than sugar cane, requiring scientists to develop ways to convert corn’s more complex sugars into simple sugars. Critics of using corn for fuel say that it takes more energy to make ethanol from corn than it takes to make regular gasoline.
A new method is being developed that may be even more promising than using corn or sugar cane as yeast food. All plants make a complex sugar called cellulose; one of the most abundant plant materials on earth. Cotton is almost completely cellulose, and some forms of cellulose can be found in many of the foods that we eat. Trees have it, grass has it, and even corn stalks contain cellulose.
Yeast does not naturally consume cellulose, so several groups of researchers have developed enzymes, which are complex molecules that operate like little machines. These enzymes break cellulose molecules down into simple sugars that the yeast can eat. Cellulose is often found with another plant compound called lignin. Lignins, a waste product of papermaking are compounds that make plants strong, and they trap cellulose. But, lignin materials extracted from waste materials can also be used for making ethanol as they can be burned (rather than fossil fuels) to power the process.
What makes this very interesting is that farms and other industries already produce tons and tons of waste materials that contain cellulose. Just imagine all the sticks and grass clippings from our yards, schools, and playgrounds could be turned into fuel for your car. Farms can also grow plants for making ethanol. Farms and timber companies can also convert their leftover
product into ethanol. President George W. Bush, in the 2006 State of the Union address mentioned switch grass when discussing fuel resources.
It's not a question of if we will stop using oil but when. Soon, we will all have to replace oil with a different, renewable source and ethanol may be the answer.