Cellulosic Ethanol: a greener alternative
By Charles Stillman, June 2006
Midwestern corn supplies 90 percent of ethanol produced domestically, but many environmentalists and energy experts would like to see corn’s hold on the ethanol market replaced with more eco-friendly, higher yielding energy sources known as cellulosic biomass. Fibrous and woody vegetation, including grasses like miscanthus and switchgrass, agricultural waste like corn husks and rice hulls, fast growing trees like hybrid poplars and waste wood from trees damaged by natural disasters and left over scrap wood from paper and saw mills are just a few examples of such sources.
Unlike corn, most varieties of cellulosic vegetation require little to no fertilizers or pesticides and emit considerably less greenhouse gases. They also provide more ethanol per acre and higher energy yields than corn. Greater adoption of cellulosic ethanol has been limited by the high costs associated with converting vegetation into ethanol. The typical conversion process begins by grinding up the biomass, soaking it in water and adding an acidic pretreatment to separate it into its primary structural components: cellulose, hemicellulose and lignin. Enzymes are added to the mixture to break down the cellulose into its constituent sugars. The sugars are then fermented and finally distilled to create high-grade ethanol.
The amount of ethanol produced and the energy content of that fuel can vary widely depending on what feedstock is used for its production. There are two main factors that must be considered when comparing ethanol produced from different sources: fuel yield per acre per year and net energy yield. Sugar beets, which are used to produce the majority of France's ethanol, yield just over 700 gallons of ethanol per acre. Brazil's sugarcane produces 662 gallons of ethanol per acre. Switchgrass, a tall prairie grass native to the US that yields over 1,000 gallons per acre, more than 3 times the yield of corn. Recent research conducted at the University of Illinois has shown that miscanthus, a tall reed like grass, can produce as much as 1,500 gallons of ethanol per acre.
The net energy yield of a fuel is commonly represented in the form of an input to output ratio of energy. The input reflects the energy required to create the fuel (including the energy employed to grow, harvest, transport and convert the feedstock into ethanol). The output represents the amount of energy the ethanol itself then provides as a fuel.
Sugarcane, at 1:8, yields about eight units of energy for every one unit invested to grow, harvest and convert the cane into ethanol. The fibrous cane material that remains after the sugar has been extracted (also known as bagasse) is used to provide heat (read: energy) in the distillation process. In most cases, this eliminates the need for energy from an external source. One unit of energy is used for every five units provided by the Miscanthus-based ethanol fuel. Switchgrass's net energy yield is slightly less, at about 1:4. Sugar beets yield nearly two units of energy for every one unit that is used to grow and convert the crop into ethanol. Corn lies near the very bottom of the list at 1:1.4.
According to the Renewable Fuels Association, last year the U.S. surpassed Brazil as the largest ethanol producer in the world. Despite having its production title stripped, Brazil remains unparallel in its use of ethanol. Today, ethanol accounts for as much as 40 percent of the non-diesel fuel used in Brazilian vehicles, as opposed to just 3 percent in the US. More than 70 percent of the automobiles sold in Brazil today are flexible-fuel vehicles, or FFVs, capable of running on gasoline, ethanol or a mix of the two.
The U.S. has sugar cane crops of its own that could be used to produce ethanol. In July, the US Department of Agriculture is due to release a study evaluating the economic feasibility of converting US sugar into ethanol. With import quotas that prop U.S. sugar prices at levels twice that found on the world market, it is believed that many farmers will likely continue converting their cane into sugar. In fact, the price of U.S. sugar is expected to continue rising due primarily to the loss of crops caused by last year’s hurricanes as well as reduced imports of Brazilian sugar, prompted by the South American country’s decision to divert more of its cane to ethanol production. Some analysts believe that continuing high oil prices and the current demand for ethanol as an alternative to MTBE will entice some U.S. sugar cane and sugar beet growers to venture into ethanol production nonetheless.
In Maui, the Hawaiian Commercial and Sugar Company and Maui Ethanol LLC have done just that, forming a partnership that is expected to produce 12 million gallons of ethanol per year from sugar cane. The economics of converting sugar cane to ethanol makes more sense in Hawaii where gasoline prices are about a dollar more per gallon than on the mainland. Growers in Louisiana and Florida also are flirting with the idea, but as of yet none have opted for ethanol over sugar. Jose Alvarez, senior vice president of operations at the Sugar Cane Growers Cooperative of Florida, says that a recent feasibility study indicated that their farmers stood to earn less than half as much for their sugar if it went towards the production of ethanol, rather than being sold as raw sugar.
Dr. Pat Westhoff is the program director with the Food and Agricultural Policy Research Institute (FAPRI) and a research associate professor in the department of agricultural economics at the University of Missouri. When asked for his reaction to corn’s seemingly illogical prominence among scores of superior biomass options such as sugar cane, Dr. Westhoff cited shear economics as the reasoning. “The amount of ethanol that can be produced from an acre of corn is less than from an acre of sugar, but an acre of sugar costs much, much more to produce in this country. Brazilian ethanol has been economical largely because sugar production costs are much lower there.”
Texas is the fourth largest sugar cane growing state, with most of the cane concentrated in the Lower Rio Grande Valley. Steve Bearden, President and CEO of Rio Grande Valley Sugar Growers, Inc., says that at this point, the organization is not considering converting its cane to ethanol. Sugar cane growers stand to make more money selling their cane to sugar refineries than to ethanol distilleries, he explains. The organization is, however, conducting a feasibility study to assess the potential of manufacturing ethanol distilleries that would be powered by sugar cane bagasse but produce ethanol from other agricultural feedstocks.
A company called BioFuels Energy Corporation is building Texas’ first cellulosic ethanol plants. The company plans to build a demonstration distillery in Raymondville, just north of Brownsville, to evaluate a number of feedstocks used in the production of various fuels including E85, a low-proof ethanol, biodiesel, and aviation fuels for airplanes and jets. The low-proof ethanol (130 proof) will be produced for use as fuel in a microturbine generator to power a fully electric car.
The BioFuels Energy Corp. also plans to build a manufacturing facility where they will construct proprietary distillation parts for cellulosic ethanol production.
Texas BioEnergy Marketing Associates (TBEMA), a subsidiary of BioFuels, is currently establishing five farmer co-ops: three in the Rio Grande Valley, one southeast of San Antonio and another one in the Coastal Bend near Corpus Christi. Each co-op will have a distillery built to process 12 million gallons of sweet sorghum-based ethanol per year. George F. Oerther, Jr., president of Biofuels Energy Corp., reports that in the event of sweet sorghum shortages, the company can use “nuisance” vegetation like water hyacinth or green wastes like grass clippings to produce ethanol.
Efforts to reduce the production costs have led many to focus on isolating and refining enzymes in an effort to speed up the conversion process. At Stephen F Austin University in Nacodoches, researchers Dr. Martynova-Van Kley and Armen Nalian are working with Pyrococcus horikoshii, a deep sea bacteria that can not only survive, but actually thrives under the harsh conditions required for the pretreatment (also known as the hydrolysis phase) of the ethanol production process. Enzymes from the deep sea bacteria can be added during the hydrolysis phase along with the chemical pretreatments, allowing for a quicker breakdown of the cellulose. Researchers are also looking at native microbes that are better suited to (and therefore faster at) consuming the cellulose found in local vegetation. Ultimately they wish to combine the individual strengths of different enzymes into “super” enzymes that they will patent and sell to industry.
Texas has large amounts of agricultural waste such as rice hulls, cotton gin waste and other crop residues that go unused every year. Large parts of the state provide prime growing environments for fuel crops like miscanthus and switchgrass. Using E85 gas produced from these sources could cut a car’s greenhouse gas emissions by as much as 87 percent over gasoline. As production costs drop, cellulosic ethanol will continue to make more sense as an alternative to gasoline. Soon, Texas could be known as much for its cellulosic ethanol as it is for its oil.