5 Things You Need to Know About How Ethanol Is Made

by Bill Siuru
07/03/2008



A Very Old Technology
While the technology and equipment is much more sophisticated today, ethanol, or ethyl alcohol, is produced basically as it has been done as long as man has been making beer and wine. As done for centuries, most ethanol today is produced by fermentation. When the feedstock is a grain like corn, the starch is first converted to sugars. Then, in the presence of the right type of yeast and in the absence of oxygen, the sugars are converted to ethyl alcohol and carbon dioxide. It is important that there is no oxygen during fermentation, otherwise you get water and carbon dioxide rather than ethanol. Ethanol can also be made from rice, wheat, sorghum, sunflower, and potatoes. In Brazil, where ethanol accounts for over 40 percent of the country's automotive fuel, sugar cane is used as the feedstock. Brazil is currently the world's biggest producer of ethanol.

Fuel or Food
Critics of using ethanol as a fuel say that the environmental benefits are nil and more important, the use of biofuels has to compete with the same feedstocks that are used for food. As we're seeing now, this means higher food prices and even food shortages. In the U.S., ethanol is mostly produced from corn that is both land and energy intensive. Experts say there is not enough agricultural land to grow enough corn for both fuel and food. The U.S. Department of Energy says corn-based ethanol provides only 26 percent more energy than required for its production, much of this being the fossil fuels used for fertilizer, diesel for tractors and trucks, and coal and natural gas for operating ethanol plants.

Government Mandate
The new Energy Independence and Security Act calls for a dramatic increase in biofuels - from 7.5 billion gallons in 2012 to 36 billion gallons in 2022. Corn- and other grain-based ethanols are expected to account for up to 15 billion gallons of these biofuels. The remaining 21 billion gallons will come from cellulosic and biomass sources.

Cellulosic Ethanol to the Rescue
Since cellulose is present in every plant, there is an abundance of low cost feedstock materials. Promising feedstock candidates include grasses and fast growing trees. The estimated 325 million tons of waste materials discarded every year - like urban wood waste, mill residues, corn stover and wheat straw - could provide as much as 30 percent of our fuel needs. Currently, switchgrass is of great interest because it contains much cellulose. An acre of grasses or other crops grown to make ethanol could produce more than twice the gallons of ethanol compared to corn, partly because the whole plant can be used. One gallon of fossil fuel can produce over five gallons of ethanol from prairie grasses.

Development Still Needed
While cellulosic biomass is cheaper to grow than corn because it requires less energy, fertilizer, herbicides, and other necessities make it substantially more expensive to process into ethanol than corn. Currently, it costs about $2.25 per gallon, about twice as much as from corn. This translates to the equivalent of $120 a barrel oil. The target is to half this by 2012. Incidentally, there is no difference between corn and cellulosic ethanol since both are ethyl alcohol. Also, ethanol cannot be transported readily through existing petroleum pipelines and must now be transported by barge, rail, or truck. This adds greatly to the cost of E85 (85-percent ethanol and 15-percent gasoline) and means E85 is still only readily available in or near corn-growing states. Finally, the oil companies have shown little interest in selling this competitor to gasoline.

Current Status for Cellulosic Ethanol
Plants to produce cellulosic ethanol, at least in demonstration quantities, are coming on line in various locations in the U.S. as well as in China and Spain. Recently, General Motors announced its partnership with Coskata to use this company's breakthrough technology to make ethanol from many feedstocks including garbage, old tires, and plant waste. It uses microorganisms that eliminate the need for costly pretreatments with enzymes. The microorganisms also ferment the material at lower temperatures and pressures to further reduce costs. A cost of about $1 per gallon is projected. The process extracts about 7.7 units of energy for every unit spent in turning feedstock into ethanol. It also reduces CO2 emissions by up to 84 percent compared to gasoline. Coskata's process uses less than a gallon of water to make a gallon of ethanol compared to three gallons or more for other processes. Coskata will deliver the first ethanol from its pilot plant to GM in late 2008, The first commercial-scale plant making 50 to 100 million gallons of ethanol should be running in 2011.

Bill Siuru is a retired USAF colonel who has been writing about automotive technology for nearly 40 years. He has a bachelor's degree in automotive engineering, a PhD in mechanical engineering and has taught engineering at West Point and the U.S. Air Force Academy.