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Cellulosic ethanol is a type of biofuel produced from lignocellulose, a structural material that comprises much of the mass of plants. It is composed mainly of cellulose, hemicellulose and lignin. Corn stover, switchgrass, miscanthus and woodchip are some of the more popular cellulosic materials for ethanol production. Cellulosic ethanol is chemically identical to ethanol from other sources, such as corn starch or sugar, but has the advantage that the lignocellulose raw material is highly abundant and diverse. However, it differs in that it requires a greater amount of processing to make the sugar monomers available to the microorganisms that are typically used to produce ethanol by fermentation. Switchgrass is the major biomass material being studied today, due to its high levels of cellulose. Cellulose, however, is contained in nearly every natural, free-growing plant, tree, and bush, in meadows, forests, and fields all over the world without agricultural effort or cost needed to make it grow. Whether distilled from agricultural crops such as corn, wheat, barley or created from celloluse, ethanol is ethyl alcohol; it is identical in chemical composition regardless of the source. Calling it cellulosic ethanol is misleading because it (cellulosic ethanol) is no different physically from corn ethanol or wheat ethanol. The ground of North American forests is littered with tons of cellulose-containing wastewood branches fallen from trees, which could be harvested and converted into ethanol automobile fuel. The processes that produce lumber and lumber products also generate cellulose waste that is discarded that could be used to produce cellulosic ethanol.
There are at least two methods of production of cellulosic ethanol (see "Production methods", below):
Neither process generates toxic emissions when it produces ethanol.
Cellulosic ethanol production currently exists at "pilot" and "commercial demonstration" scale, including a plant in China engineered by SunOpta Inc. and owned and operated by China Resources Alcohol Corporation that is currently producing cellulosic ethanol from corn stover (stalks and leaves) on a continuous, 24-hour per day rate.
According to US Department of Energy studies conducted by the Argonne Laboratories of the University of Chicago, one of the benefits of cellulosic ethanol is that it reduces greenhouse gas emissions (GHG) by 85% over reformulated gasoline. By contrast, starch ethanol (e.g., from corn), which most frequently uses natural gas to provide energy for the process, reduces GHG emissions by 18% to 29% over gasoline. Sugar ethanol is cheaper than corn ethanol. Cellulosic ethanol from sugarcane bagasse, reduces greenhouse gas emissions by as much as cellulosic ethanol. In both cases the waste lignin becomes fuel to provide the energy for the process with some excess to provide electricity for the grid.
Ethanol, if made from cellulose, emits 80 percent less global warming pollution than gasoline.
Additional recommended knowledge
The first attempt at commercializing a process for ethanol from wood was done in Germany in 1898. It involved the use of dilute acid to hydrolyze the cellulose to glucose, and was able to produce 7.6 liters of ethanol per 100 kg of wood waste (18 gal per ton). The Germans soon developed an industrial process optimized for yields of around 50 gallons per ton of biomass. This process soon found its way to the United States, culminating in two commercial plants operating in the southeast during World War I. These plants used what was called "the American Process" — a one-stage dilute sulfuric acid hydrolysis. Though the yields were half that of the original German process (25 gallons of ethanol per ton versus 50), the throughput of the American process was much higher. A drop in lumber production forced the plants to close shortly after the end of World War I. In the meantime, a small, but steady amount of research on dilute acid hydrolysis continued at the USDA's Forest Products Laboratory.
In April 2004, Iogen Corporation, a Canadian biotechnology firm, became the first business to commercially sell cellulosic ethanol, though in very small quantities. The primary consumer thus far has been the Canadian government, which, along with the United States government (particularly the Department of Energy's National Renewable Energy Laboratory), has invested millions of dollars into assisting the commercialization of cellulosic ethanol.
Another company which appears to be nearing commercialization of cellulosic ethanol is Spain's Abengoa Bioenergy . Abengoa has and continues to invest heavily in the necessary technology for bringing cellulosic ethanol to market. Using process and pre-treatment technology from SunOpta Inc.(NASDAQ: STKL), Abengoa is building a 5 million gallon cellulosic ethanol facility in Spain and has recently entered into a strategic research and development agreement with Dyadic International, Inc. (AMEX: DIL), to create a new and better enzyme mixtures which may be used to improve both the efficiencies and cost structure of producing cellulosic ethanol.
On December 21, 2006, SunOpta Inc. announced a Joint Venture with GreenField Ethanol, Canada's largest ethanol producer. The joint venture will build a series of large-scale plants that will make ethanol from wood chips, with SunOpta Inc. and GreenField each taking 50% ownership. The first of these plants will be 10 million gallons per year, which appears to be the first true "commercial scale" cellulosic ethanol plant in the world. Under 1 million gallons per year (MMgy) is considered "Pilot Scale", greater than 1 MMgy but less than 10 MMgy is defined as "commercial demonstration", while a plant that produces 10 MMgy per year or greater is true "commercial scale". Despite the multiple commercial demonstration cellulosic ethanol plants SunOpta has been involved with, media reports continue to state that cellulosic ethanol is an unproven, "experimental" technology. The 10 MMgy SunOpta/GreenField cellulosic ethanol plant is intended to demonstrate that large-scale cellulosic ethanol is commercially viable immediately.
President Bush, in his State of the Union address delivered January 31, 2006, proposed to expand the use of cellulosic ethanol. In his State of the Union Address on January 23, 2007, President Bush announced a proposed mandate for 35 billion gallons of ethanol by 2017. It is widely recognized that the maximum production of ethanol from corn starch is 15 billion gallons per year, implying a mandated production of some 20 billion gallons per year of cellulosic ethanol by 2017. Bush's plan includes $2 billion funding for cellulosic ethanol plants, with an additional $1.6 billion announced by the USDA on January 27, 2007.
In March 2007, the US government awarded $385 million in grants aimed at jumpstarting ethanol production from nontraditional sources like wood chips, switchgrass and citrus peels. Half of the six projects chosen will use thermochemical methods and half will use cellulosic ethanol methods.
The American company Range Fuels announced in July 2007 that it was awarded a construction permit from the state of Georgia to build the first commercial-scale 100-million-gallon-per-year cellulosic ethanol plant in the United States . Construction began in November, 2007.
There are two ways of producing alcohol from cellulose:
They both include distillation as the final step to isolate the pure ethanol.
Cellulolysis (biological approach)
There are four or five stages to produce ethanol using a biological approach:
Although cellulose is the most abundant plant material resource, its susceptibility has been curtailed by its rigid structure. As the result, an effective pretreatment is needed to liberate the cellulose from the lignin seal and its crystalline structure so as to render it accessible for a subsequent hydrolysis step . By far, most pretreatments are done through physical or chemical means. In order to achieve higher efficiency, some researchers seek to incorporate both effects .
To date, the available pretreatment techniques include acid hydrolysis, steam explosion, ammonia fiber expansion, alkaline wet oxidation and ozone pretreatment . Besides effective cellulose liberation, an ideal pretreatment has to minimize the formation of degradation products because of their inhibitory effects on subsequent hydrolysis and fermentation processes . The presence of inhibitors will not only further complicate the ethanol production but also increase the cost of production due to entailed detoxification steps. Even though pretreatment by acid hydrolysis is probably the oldest and most studied pretreatment technique, it produces several potent inhibitors including furfural and hydroxymethyl furfural (HMF) which are by far regarded as the most toxic inhibitors present in lignocellulosic hydrolysate . In fact, Ammonia Fiber Expansion (AFEX) is the sole pretreatment which features promising pretreatment efficiency with no inhibitory effect in resulting hydrolysate 
The cellulose molecules are composed of long chains of sugar molecules of various kinds. In the hydrolysis process, these chains are broken down to free the sugar, before it is fermented for alcohol production.
There are two major cellulose hydrolysis (cellulolysis) processes: a chemical reaction using acids, or an enzymatic reaction.
In the traditional methods developed in the 19th century and at the beginning of the 20th century, hydrolysis is performed by attacking the cellulose with an acid. Dilute acid may be used under high heat and high pressure, or more concentrated acid can be used at lower temperatures and atmospheric pressure. A decrystalized cellulosic mixture of acid and sugars reacts in the presence of water to complete individual sugar molecules (hydrolysis). The product from this hydrolysis is then neutralized and yeast fermentation is used to produce ethanol. As mentioned, a significant obstacle to the dilute acid process is that the hydrolysis is so harsh that toxic degradation products are produced that can interfere with fermentation. Concentrated acid must be separated from the sugar stream for recycle (simulated moving bed (SMB) chromatographic separation for example) to be commercially attractive.
BlueFire Ethanol Fuels utilizes post-sorted MSW, rice and wheat straws, wood waste and other agricultural residues and implements significant proprietary improvements to concentrated acid hydrolysis. The Technology is unique in that, for the first time, it enables widely available cellulosic materials, or more commonly, biomass, to be converted into sugar in an economically viable manner, thereby providing an inexpensive raw material for fermentation or chemical conversion into any of a hundred different specialty and/or commodity chemicals. In February of 2007, BlueFire Ethanol was among 6 companies that received a grant from the US Department of Energy for $40M to promote development of cellulosic ethanol refineries.
This reaction occurs at body temperature in the stomach of ruminants such as cows and sheep, where the enzymes are produced by bacteria. This process uses several enzymes at various stages of this conversion. Using a similar enzymatic system, lignocellulosic materials can be enzymatically hydrolyzed at a relatively mild condition (50oC and pH5), thus enabling effective cellulose breakdown without the formation of byproducts that would otherwise inhibit enzyme activity. By far, all major pretreatment methods, including dilute acid pretreatment, require enzymatic hydrolysis step to achieve high sugar yield for ethanol fermentation 
Various enzyme companies have contributed significant technological breakthroughs in cellulosic ethanol through the mass production of enzymes for hydrolysis at competitive prices.
Iogen Corporation is a Canadian producer of enzymes for an enzymatic hydrolysis process that uses "specially engineered enzymes". The raw material (wood or straw) has to be pre-treated to make it amenable to hydrolysis.
Another Canadian company, SunOpta Inc. markets a patented technology known as "Steam Explosion" to pre-treat cellulosic biomass, overcoming its "recalcitance" to make cellulose and hemicellulose accessible to enzymes for conversion into fermenatable sugars. SunOpta designs and engineers cellulosic ethanol biorefineries and its process technologies and equipment are in use in the first 3 commercial demonstration scale plants in the world : Verenium (formerly Celunol Corporation)'s facility in Jennings, Louisiana, Abengoa's facility in Salamanca, Spain, and a facility in China owned by China Resources Alcohol Corporation (CRAC). The CRAC facility is currently producing cellulosic ethanol from local corn stover on a 24-hour a day basis utilizing SunOpta's process and technology.
Genencor and Novozymes are two other companies that have received United States government Department of Energy funding for research into reducing the cost of cellulase, a key enzyme in the production of cellulosic ethanol by enzymatic hydrolysis.
Other enzyme companies, such as Dyadic International, Inc. (AMEX: DIL), are developing genetically engineered fungi which would produce large volumes of cellulase, xylanase and hemicellulase enzymes which can be utilized to convert agricultural residues such as corn stover, distiller grains, wheat straw and sugar cane bagasse and energy crops such as switch grass into fermentable sugars which may be used to produce cellulosic ethanol.
Verenium (NASDAQ: VRNM), the new name of recently merged Diversa and Celunol Corporations, operates a pilot cellulosic ethanol plant in Jennings, Louisiana and is building a 1.4 million gallon per year demonstration plant on adjacent land to be completed by the end of 2007 and begin operation in early 2008. Vernium is the first publicly traded company with integrated, end-to-end capabilities to make cellulosic biofuels.
Traditionally, baker’s yeast (Saccharomyces cerevisiae), has long been used in brewery industry to produce ethanol from hexoses (6-carbon sugar). Due to the complex nature of the carbohydrates present in lignocellulosic biomass, a significant amount of xylose and arabinose (5-carbon sugars derived from the hemicellulose portion of the lignocellulose) is also present in the hydrolysate. For example, in the hydrolysate of corn stover, approximately 30% of the total fermentable sugars is xylose. As a result, the ability of the fermenting microorganisms to utilize the whole range of sugars available from the hydrolysate is vital to increase the economic competitiveness of cellulosic ethanol and potentially bio-based chemicals.
In recent years, metabolic engineering for microorganisms used in fuel ethanol production has shown significant progress . Besides Saccharomyces cerevisiae, microorganisms such as Zymomonas mobilis and Escherichia coli have been targeted through metabolic engineering for cellulosic ethanol production.
Recently, engineered yeasts have been described efficiently fermenting xylose  and arabinose , and even both together . Yeast cells are especially attractive for cellulosic ethanol processes as they have been used in biotechnology for hundred of years, as they are tolerant to high ethanol and inhibitor concentrations and as they can grow at low pH values which avoids bacterial contaminations.
Combined hydrolysis and fermentation
Some species of bacteria have been found capable of direct conversion of a cellulose substrate into ethanol. One example is Clostridium thermocellum, which utilizes a complex cellulosome to break down cellulose and synthesize ethanol. However, C. thermocellum also produces other products during cellulose metabolism, including acetate and lactate, in addition to ethanol, lowering the efficiency of the process. Some research efforts are directed to optimizing ethanol production by genetically engineering bacteria that focus on the ethanol-producing pathway.
Gasification process (thermochemical approach)
The gasification process does not rely on chemical decomposition of the cellulose chain (cellulolysis). Instead of breaking the cellulose into sugar molecules, the carbon in the raw material is converted into synthesis gas, using what amounts to partial combustion. The carbon monoxide, carbon dioxide and hydrogen may then be fed into a special kind of fermenter. Instead of sugar fermentation with yeast, this process uses a microorganism named “Clostridium ljungdahlii” . This microorganism will ingest (eat) carbon monoxide, carbon dioxide and hydrogen and produce ethanol and water. The process can thus be broken into three steps:
A recent study has found another Clostridium bacterium that seems to be twice as efficient in making ethanol from carbon monoxide as the one mentioned above
Alternatively, the synthesis gas from gasification may be fed to a catalytic reactor where the synthesis gas is used to produce ethanol and other higher alcohols through a thermochemical process . This process can also generate other types of liquid fuels, an alternative concept under investigation by at least one biofuels company
Construction of pilot scale lignocellulosic ethanol plants requires considerable financial support through grants and subsidies. On 28th Feb 2007, the US Dept of Energy announced $385 million in grant funding to 6 cellulosic ethanol plants. This grant funding accounts for 40% of the investment costs. The remaining 60% comes from the promoters of those facilities. Hence, a total of $1 billion will be invested for approximately 140 million gallon capacity. This translates into $7/annual gallon in capital investment costs for pilot plants; future capital costs are expected to be lower. Corn to ethanol plants cost roughly $1 - $3/annual gallon capacity.
The quest for alternative sources of energy has provided many ways to produce electricity, such as wind farms, hydropower, or solar cells. However, about 40% of total energy consumption is dedicated to transportation (i.e., cars, planes, lorries/trucks, etc.) and currently requires energy-dense liquid fuels such as gasoline, diesel fuel, or kerosene. These fuels are all obtained by refining petroleum. This dependency on oil has two major drawbacks: burning fossil fuels such as oil contributes to global warming; and for net-consuming countries like the United States, importing oil creates a dependency on oil-producing countries.
As of 2007, ethanol is produced mostly from sugars or starches, obtained from fruits and grains. In contrast, cellulosic ethanol is obtained from cellulose, the main component of wood, straw and much of the plants. Since cellulose cannot be digested by humans, the production of cellulose does not compete with the production of food. The price per ton of the raw material is thus much cheaper than grains or fruits. Moreover, since cellulose is the main component of plants, the whole plant can be harvested. This results in much better yields per acre—up to 10 tons, instead of 4 or 5 tons for the best crops of grain.
The raw material is plentiful. Cellulose is present in every plant, in the form of straw, grass, and wood. Most of these "bio-mass" products are currently discarded.. It is estimated that 323 million tons of cellulose containing raw materials that could be used to create ethanol are thrown away each year.  This includes 36.8 million dry tons of urban wood wastes 90.5 million dry tons of primary mill residues 45 million dry tons of forest residues and 150.7 million dry tons of corn stover and wheat straw . Transforming them into ethanol using efficient and cost effective hemi(cellulase) enzymes or other processes might provide as much as 30% of the current fuel consumption in the United States—and probably similar figures in other oil-importing regions like China or Europe. Moreover, even land marginal for agriculture could be planted with cellulose-producing crops like switchgrass, resulting in enough production to substitute for all the current oil imports into the United States. Paper, cardboard, and packaging comprise a substantial part of the solid waste sent to landfills in the United States each day. These all contain cellulose that should be transformable into cellulosic ethanol . Reduction of the disposal of solid waste through celulosic ethanol conversion would reduce solid waste disposal costs by local and state governments.
In June 2006, a U.S. Senate hearing was told that the current cost of producing cellulosic ethanol is US $2.25 per US gallon (US $0.59/litre). This is primarily due to the current poor conversion efficiency. At that price it would cost about $120 to substitute a barrel of oil (42 gallons), taking into account the lower energy content of ethanol. However, the Department of Energy is optimistic and has requested a doubling of research funding. The same Senate hearing was told that the research target was to reduce the cost of production to US $1.07 per US gallon (US $0.28/litre) by 2012.
Environmental effects: corn-based vs. grass-based
Today, there is only a small amount of switchgrass dedicated for ethanol production. In order for it to grown on a large-scale production it must compete with existing uses of agricultural land, mainly for the production of crop commodities. Of the United States 2 billion acres of land, 33% are forestland, 26% pastureland and grassland, and 20% crop land. A study done by the U.S. Departments of Energy and Agriculture in 2005, determined whether there were enough available land resources to sustain production of over 1 billion dry tons of biomass annually to replace 30% or more of the nation’s current use of liquid transportation fuels. The study found that there could be 1.3 billion dry tons of biomass available for ethanol use, by making little changes in agricultural and forestry practices and meeting the demands for forestry products, food, and fiber. A recent study done by the University of Tennessee reported that as many as 100,000,000 acres (400,000 km²) of cropland and pasture will need to be allocated to switchgrass production in order to offset petroleum use by 25 percent.
Currently, corn is easier and less expensive to process into ethanol in comparison to cellulosic ethanol. The Department of Energy estimates that it costs about $2.20 per gallon to produce cellulosic ethanol, which is twice as much as ethanol from corn. Enzymes that destroy plant cell wall tissue cost 30 to 50 cents per gallon of ethanol compared to 3 cents per gallon for corn. The Department of Energy hopes to reduce this cost to $1.07 per gallon by 2012 to be effective. However, cellulosic biomass is cheaper to produce than corn, because it requires fewer inputs, such as energy, fertilizer, herbicide, and is accompanied by less soil erosion and improved soil fertility. Additionally, nonfermentable and unconverted solids left after making ethanol can be burned to provide the fuel needed to operate the conversion plant and produce electricity. Energy used to run corn-based ethanol plants is derived from coal and natural gas.
One of the major reasons for increasing the use of biofuels is to reduce greenhouse gas emissions. In respect to gasoline, ethanol burns cleaner with a greater efficiency, thus putting less carbon dioxide and overall pollution in the air. Additionally, only low levels of smog are produced from combustion. According to the U.S. Department of Energy, ethanol from cellulose reduces green house gas emission by 90 percent, when compared to gasoline and in comparison to corn-based ethanol which decreases emissions by 10 to 20 percent. Carbon dioxide gas emissions are shown to be 85% lower than those from gasoline. Cellulosic ethanol contributes little to the greenhouse effect and has a five times better net energy balance than corn-based. When used as a fuel, cellulosic ethanol releases less sulfur, carbon monoxide, particulates, and greenhouse gases. Cellulosic ethanol should earn producers carbon reduction credits, higher than those given to producers who grow corn for ethanol, which is about 3 to 20 cents per gallon.
It takes 1.2 gallons of fossil fuel to produce 1 gallon of ethanol from corn. This total includes the use of fossil fuels used for fertilizer, tractor fuel, ethanol plant operation, etc. Research has shown that 1 gallon of fossil fuel can produce over 5 gallons of ethanol from prairie grasses, according to Terry Riley, President of Policy at the Theodore Roosevelt Conservation Partnership. The United States Department of Energy concludes that corn-based ethanol provides 26 percent more energy than it requires for production, while cellulosic ethanol provides 80 percent more energy. Cellulosic ethanol yields 80 percent more energy than is required to grow and convert it. The process of turning corn into ethanol requires about 1,700 gallons of water for every gallon for every 1 gallon of ethanol produced. Additionally, each gallon of ethanol leaves behind 12 gallons of waste that must be disposed.  Grain ethanol uses only the edible portion of the plant. Expansion of corn acres for the production of ethanol poses threats to biodiversity. Corn lacks a strong root system, therefore, when produced, it causes soil erosion. This has a direct effect on soil particles, along with excess fertilizers and other chemicals, washing into local waterways, damaging water quality and harming aquatic life. Planting riparian areas can serve as a buffer to waterways, and decrease runoff.
Cellulose is not used for food and can be grown in all parts of the world. The entire plant can be used when producing cellulosic ethanol. Switchgrass yields twice as much ethanol per acre than corn. Therefore, less land is needed for production and thus less habitat fragmentation. Biomass materials require fewer inputs, such as fertilizer, herbicides, and other chemicals that can pose risks to wildlife. Their extensive roots improve soil quality, reduce erosion, and increase nutrient capture. Herbaceous energy crops reduce soil erosion by greater than 90%, when compared to conventional commodity crop production. This can translate into improved water quality for rural communities. Additionally, herbaceous energy crops add organic material to depleted soils and can increase soil carbon, which can have a direct effect on climate change. As compared to commodity crop production, biomass reduces surface runoff and nitrogen transport. Switchgrass provides an environment for diverse wildlife habitation, mainly insects and ground birds. Conservation Resource Program (CRP) land is composed of perennial grasses, which are used for cellulosic ethanol, and may be available for use.
Switchgrass is a native prairie grass that is known for its hardiness and rapid growth. This perennial grows during the warm season of the year and grows to 2-6 feet tall. Switchgrass can be grown in most parts of the United States, including swamplands, plains, streams, and along the shores. It is resistant to many diseases and pests and can produce high yields with low applications of fertilizer and other chemicals. It is also tolerant to poor soils, flooding, and drought and improves soil quality and prevents erosion.
Switchgrass is an approved cover crop for land protected under the federal Conservation Reserve Program (CRP). CRP is land where crops recently grew, and now the producer gets paid a fee to stop growing crops on this land. This program reduces soil erosion, enhances water quality, and increases wildlife habitat. CRP land serves as a habitat for upland game, such as pheasants and ducks, and a number of insects. Switchgrass for biofuel production has been considered for use on Conservation Reserve Program (CRP) land, which could increase ecological sustainability and lower the cost of the CRP program. However, CRP rules would have to be modified to allow this economic use of the CRP land.
Prominent cellulosic ethanol researchers
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cellulosic_ethanol". A list of authors is available in Wikipedia.|