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Fields of corn or wheat are common sights in rural Canada, and are usually associated with food. But these grains are not just for cinnamon toast and corn flakes anymore. They also end up in Canadians’ gas tanks, in the form of fuel ethanol. This first generation biofuel is produced commercially by breaking down corn and wheat starch into sugar, then using yeast to ferment the sugar into ethanol. Ethanol production plants are considered biorefineries because they convert a grain biomass into biofuel using enzymes and living microorganisms.
Ethanol is a liquid alcohol that can be used like gasoline in vehicles with internal combustion engines. These engines compress liquid fuel, ignite it with a spark, and capture the energy that is released during the combustion reaction to power the vehicle. Over a century ago, Henry Ford designed the first Model T car to run on gasoline, ethanol, or a mixture of the two.
The Biochemical Path from Kernels to Kick-Start
Ethanol production plants in Ontario and Quebec mainly use corn kernels as a feedstock (input material), and those in Western Canada mainly use wheat kernels, because that is the geographical distribution of corn and wheat agriculture. Corn accounts for over half of the Canadian ethanol feedstock, so it will be the ‘model grain’ for the biochemical conversion, but the processes are basically the same for wheat.
There are five main steps in the ethanol production process (also detailed in Figure 1):
1. Milling: Whole corn kernels are mechanically ground into a flour, or meal. The meal is mainly starch, a biological polymer made up of chains of covalently bonded sugar molecules.
2. Liquefaction: Water is added to the corn meal to make ‘slurry.’ The slurry is heated to break apart the starch granules. The enzyme alpha-amylase is added to catalyze the breakdown of the long starch molecules into smaller pieces.
3. Saccharification: Starch polysaccharide fragments are broken down into the simple sugar glucose. This reaction is catalyzed by another enzyme called glucoamylase.
4. Fermentation: Single celled microorganisms called yeast are added to the slurry. Glucose is used as a food source by the yeast in a biochemical process called fermentation. Yeast cells get energy by fermenting the glucose into ethanol.
5. Distillation, Dehydration and Denaturation: The product of the fermentation tanks is only 10-15% ethanol, so it must be concentrated. Ethanol has a lower boiling point than water, so it can be selectively evaporated and re-condensed. This distillation process produces ethanol that is 95% pure. The remaining 5% is residual water, which is removed by sieves to produce dehydrated, 100% ethanol. A small amount of gasoline is added as a denaturant to make fuel ethanol undrinkable.
There are two main byproducts of corn ethanol production: carbon dioxide (CO2) and distillers’ grains. CO2 is produced by yeast as a byproduct of the fermentation reaction. It is often released into the atmosphere, but it can be captured and used to make carbonated beverages or dry ice (frozen CO2) for cold storage applications, or used in vegetable greenhouses (for photosynthesis). Distillers’ grains are the residue from the fermentation tanks, containing all the non-fermentable components of the corn kernels plus the added yeast. It is valuable as a high-protein ingredient in livestock feed.
Figure 1: Overview of the Biochemistry of Corn Ethanol Production.
The biochemical pathway from corn kernels to fuel ethanol is summarized in words, molecular formulae, and structure diagrams.
For clarity, a simplified molecular formula is given for starch. As a large biological polymer, starch has an indefinite molecular
formula and structure due to variable branch points for the glucose chains. The alpha-1,4-glycosidic bond between glucose
molecules is characteristic of starch polymers, and is the substrate for alpha-amylase and glucoamylase enzymes.
Inset Photo credits: Maize Corn By Joel Penner from Winnipeg, Canada (Expecting Edibility) [CC-BY-2.0], via Wikimedia Commons (also used for header photo above), Yeast By Bob Blaylock (Own work) [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons
Corn Ethanol – A Widely Used Renewable Fuel
Canadian biorefineries make around two billion litres of ethanol per year (world’s 5th largest producer), most of which is blended into gasoline. All gasoline-powered vehicles built since the 1980s can run on a blend of up to 10% ethanol (E10) without any engine modifications. Some North American car companies make Flex Fuel vehicles with modified engines that can use blends up to 85% ethanol and 15% gasoline (E85). Canada’s Renewable Fuel Standard, enacted in 2010, requires an average of 5% renewable fuel content in non-renewable fossil fuels. Corn ethanol is renewable, because new corn crops are grown every year to replenish the biomass. That is a stark contrast to the millions of years it took to create the world’s finite supply of oil.
Some Good News: Combating Climate Change with Corn
One of the main benefits of using corn ethanol as fuel is a reduction in greenhouse gas (GHG) emissions. Transportation accounted for 28% of Canada’s GHG emissions in 2010, most of which was CO2 released by burning fossil fuels like gasoline (Environment Canada). Fossil fuels store carbon. When they are combusted, the CO2 byproduct is released to the atmosphere, where it is a powerful GHG and contributes to climate change. There is no way to turn it back into oil. In contrast, some of the CO2 released by corn ethanol combustion is absorbed by a new corn crop for photosynthesis, and incorporated into the sugar molecules that will be converted into ethanol again.
However, the GHG picture is much more complicated because fossil fuels are often burned at many steps in the production of fuel ethanol. For example, farmer’s tractors use diesel fuel, the trucks that transport corn to biorefineries use diesel fuel, and the biorefineries themselves sometimes use fossil fuels for power. Therefore, a lifecycle analysis must be done to fully understand the GHG impact of biofuels compared to conventional fossil fuels. Although estimates vary widely, a recent Canadian lifecycle analysis determined that using pure corn ethanol (E100) as fuel reduces GHG emissions by around 45% compared to gasoline. E5 or E10 blends would have proportionally smaller reductions in GHG emissions.
Remember that the Canadian Renewable Fuel Standard mandates 5% renewable content in gasoline. That 5% level is currently being met with corn/wheat ethanol (E5). What about the E85 blend that can be used in Flex Fuel vehicles? Some Canadian companies with large vehicle fleets use E85, but it is not yet commercially available. There are only three or four gas stations in Canada that sell E85, all in Ontario. In contrast, there are over 2,000 gas stations with E85 pumps in the U.S., though that is still less than 2% of total fuel stations.
Global Dynamics of Ethanol Production 2012
The U.S. is the world’s largest producer and exporter of corn, and also the world leader in fuel ethanol production at 50 billion litres per year. The U.S. Renewable Fuel Standard mandates 9% ethanol in gasoline this year, and about 40% of the U.S. corn crop goes to ethanol production. (In comparison, about 10% of Canada’s corn crop is converted to ethanol.) Because the 2012 U.S. corn harvest is reduced due to drought, there is international pressure for the government to waive their ethanol mandate for one year. The Food and Agricultural Organization of the United Nations appealed for a waiver out of concern for decreasing supply and increasing corn prices on the global market. So far, the U.S. ethanol mandate is unchanged. In contrast, the European Union is capping their allowable food crop-based biofuel content at 5% (E5), both to reduce pressure on food prices and prevent land from being cleared for biofuel crop cultivation.
Some Modestly Good News: Corn Ethanol and Energy Balance
Ethanol is a great energy source, but corn kernels don’t turn into ethanol all by themselves. If the input energy to make a fuel is greater than the output energy, that fuel has a negative energy balance (not good). If the output energy is greater than the input energy, the fuel has a positive energy balance (good). In the early days of ethanol production, many studies found a negative energy balance. However, recent Canadian and American lifecycle analyses have found a modestly positive energy balance, with corn ethanol providing up to two times the energy it takes to produce. The improvement is largely due to new biorefineries being built to modern energy-efficient standards. Canadian corn ethanol may have a slightly better positive energy balance because less nitrogen fertilizer is used and corn is not irrigated in Canada.
Some Potentially Discouraging News: The Food versus Fuel Debate
A real concern with corn ethanol is the economics and ethics of using cropland to grow fuel biomass instead of food. Critics of first generation biofuels like corn ethanol, argue that diverting food for fuel production increases food prices and makes it even harder for the world’s poor to afford adequate nutrition. Corn is a renewable feedstock, but its supply is determined by the success of each harvest. When agricultural conditions are good, there may be plenty of corn for human food, animal feed and biofuel production. But when harvests suffer due to conditions like the summer 2012 drought, the supply of corn is reduced. When the supply of a commodity (anything valuable that is bought, sold or traded), such as corn, goes down, the price goes up (see insert on page 3).
Of course, this ‘food versus fuel’ debate has another side. Fuel ethanol proponents point to studies that show that increased fossil fuel costs (such as diesel used by agricultural machinery and food transportation vehicles) have a much bigger impact on food prices than competition with biofuels. There is also evidence that so far in North America, increasing crop yields have met the demand for corn for ethanol production, not clearing more land for agriculture.
There are certainly no easy answers because the global food chain and biofuel industry are interconnected in complicated ways. However, there is increasing global awareness of the possible drawbacks of first generation food crop-based biofuels, and a push towards second generation biofuels that use non-food feedstock like agricultural, restaurant and municipal waste.
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