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Feature Articles : Jun 15, 2009 (Vol. 29, No. 12)

Alternative Feedstocks Boost Ethanol Production

Industry Increasingly Relies upon Cellulosic Biofuels to Meet Government Mandates
  • Vicki Glaser

Members of the biofuels industry are ready to meet the challenge of producing replacements for petrochemical fuels that will be cost-competitive and renewable, and will meet the increasingly stringent demands of the green revolution. This was the consensus at CHI’s recent “Advanced Biofuels Development Summit.”

Optimism pervaded the presentations of biological, biochemical, genetic, and microbial strategies for enhancing corn ethanol production, developing cellulosic ethanol products, and innovating methods for producing advanced biofuels. The speakers appeared to be in agreement that no one technology will win out; instead, a variety of viable current and emerging technologies will contribute to meeting biofuel needs.

Geography may determine which type of biofuel technology is most readily adopted in a specific region, depending on what type of feedstock and biomass is locally available, thereby maximizing local resources and minimizing the energy and cost required to transport these resources.

Michael Blaylock, Ph.D., vp of systems development at Edenspace Systems, reported on the status of Energy Corn™, a feedstock designed to lower the cost of producing cellulosic biofuels from corn stover. The company’s technology platform, based on identifying promising cellulose genes, transforming crop plants with candidate genes, and evaluating the effects on growth, yield, and cellulose hydrolysis would be applicable to a variety of energy crops including switchgrass, sorghum, and sugar cane.

Edenspace has demonstrated targeted enzyme expression and activity, with no evidence of negative effects on plant health. Enhanced glucan conversion with a reduced need for cellulose loading allows Energy Corn to yield cost savings, according to Dr. Blaylock. He described corn and corn stover—products of an annual domesticated crop in abundant supply, with low marginal costs of production, low acceptance barriers to farmers, and relative ease of bioengineering—as “the most promising near-term, high-volume source of cellulosic biomass for ethanol” and “a bridging crop between first- and second-generation bioethanol. High-biomass perennial crops such as miscanthus and switchgrass offer excellent longer-term potential,” he added.

Ethanol can be extracted, with varying degrees of complexity, from all three main components of corn: the endosperm, the germ, and the fiber—the latter two yielding cellulosic ethanol. Cellulose is key for U.S. fuel needs, according to Scott Kohl, technical director at ICM, who suggested that excess cellulose currently available in the U.S.—which includes corn fiber, switchgrass, corn stover, wheat straw, wood waste, and energy crops—could be sufficient to replace imported petroleum products.

The main economic barrier to increased cellulose production is the current high operating expenses associated with enzyme hydrolysis, according to Kohl. The next-most critical barrier to commercialization of cellulosic ethanol is the need for organisms capable of efficient fermentation of holocellulose, which contains up to 40% C5 sugars.

Kohl asserted that a genetically modified organism (GMO) will most likely be needed, increasing the cost and time of the regulatory approval process. One of the ways to offset these costs is to target demand for other byproducts of fermentation such as succinic acid, butanol, lactic acid, and higher-value chemicals including acetaldehyde, acetic acid, acetone, and glycerol.

Cellulosic Ethanol Gains Ground

Wes Bolsen, CMO and head of government affairs at Coskata, discussed a recent Sandia National Labs and General Motors study demonstrating that 90 billion gallons of feedstock-flexible ethanol is possible in the U.S. without a significant change in current land use. The two major pathways used to produce cellulosic biofuels have traditionally involved the conversion of biomass using either biochemical (a combination of enzymatic hydrolysis and fermentation) or thermochemical (gasification and catalysis) methods, he explained.

Bolsen described Coskata’s hybrid approach based on its Flex Ethanol™ technology, which combines gasification and fermentation in a thermo-biological pathway to produce fuel-grade ethanol that it contends can be cost-competitive with gasoline. The process is able to yield more than 100 gallons of ethanol per ton of dry biomass.

Gasification of a carbon source “is commercially viable today,” Bolsen told the conference attendees, and Flex Ethanol technology can accommodate virtually any carbon-based feedstock, from traditional agricultural sources and construction waste to plastic, tires, and wood chips, converting the biomass to syngas, he said. “There are eight to ten different technologies we can use for front-end gasification.”

Bolsen predicted that cellulosic ethanol production processes will become increasingly efficient at reducing carbon emissions. Coskata’s hybrid approach achieves as much as a 96% reduction in CO2, he noted. The next major issue in green fuel production will be water imbalance. Flex Ethanol technology has one of the lowest net water use numbers, according to Bolsen, compared to two to three gallons of water per gallon of gasoline produced, and two to four gallons of water per gallon of corn ethanol.

Further, Bolsen reported that Coskata has licensed a variety of anaerobic bacterial strains capable of converting both CO and H2, and has patents pending for its bioreactor designs, which are scalable and capable of carrying out fermentation or converting syngas to ethanol at low-to-moderate pressures and low temperatures. The company is preparing for start-up of a semi-scale facility to demonstrate cost-effective cellulosic ethanol production.

By 2012, Coskata envisions commercial production of 50–60 million gallons of ethanol per year, made by gasification of approximately 1,500 dry tons of biomass per day. With a projected production cost of $1–$1.50/gallon, Flex Ethanol will be cost-competitive with gasoline, claimed  Bolsen.

Qteros is banking on its Q Microbe™ technology to make ethanol production from cellulose both cost-effective and commercially viable. Q Microbe is a lollipop-shaped microorganism that expresses a variety of plant-degrading enzymes, including cellulases, xylanases, and ethanol dehydrogenases, which are suitable for breaking down a range of feedstocks. Enzyme expression adapts to the feedstock available, explained Jef Sharp, evp at Qteros. If cellulose is the predominant feedstock, for example, cellulases are the main enzymes expressed by the microbe. Replacing cellulose with xylan results in the organisms producing more xylanase than cellulose.

Q Microbe performs biomass breakdown and fermentation in a single step and can ferment both C5 and C6 sugars simultaneously, producing ethanol as the primary product. It hydrolyzes and liquefies biomass to yield a solution from which ethanol can be distilled.

Qteros is working with the U.S. Department of Energy and the Department of Agriculture and is exploring scale-up with potential industrial partners. The company expects to begin operation of an internal pilot plant in 2009 and an external pilot plant in 2010, with a large-scale demonstration plant projected for 2011. Qteros plans to license Q Microbe technology to ethanol producers.

Sharp predicted that the cost barrier for cellulosic ethanol production will be overcome within the next few months. This would open the market to ethanol that could be produced from the “420 million tons of biomass easily harvestable in the U.S.” Sharp also said that the ethanol generated from that biomass could replace at least half—about 45 billion gallons—of the oil the U.S. imports annually.

While Q Microbe is not a GMO—it is a naturally occurring anaerobe that lives under the soil—the company is confident that the patents it is pursuing on the use of the microbe for ethanol production will yield a valuable intellectual property portfolio. Qteros has a genetic-engineering program in place to optimize the microbe for use in large-scale ethanol production.

Manipulating Genomes

Current industry biofuel production goals for reducing the carbon footprint envision a 20% reduction in CO2 from ethanol facilities, a 50% reduction for advanced biofuels, and an 80% reduction for cellulosic biofuels.

Aristides Patrinos, Ph.D., president of Synthetic Genomics, stated that current energy-related carbon emissions total eight billion tons per year, about half of which remains in the atmosphere contributing to increasing greenhouse gas concentrations.

Achieving zero net carbon emissions is possible, even with continued burning of fossil fuels, said Dr. Patrinos, but only with the development of advanced biofuel production processes, and carbon capture and disposal or recycling technologies. The concurrent development of hydrogen fuels and alternative biological energy sources will help reduce carbon emissions and greenhouse gas concentrations.

Dr. Patrinos highlighted advances in genomics, structural biology, pathway analysis, and systems biology as driving forces in the move toward molecule-based cell simulation. He described ongoing work at The J. Craig Venter Institute to produce artificial chromosomes and achieve genome transplantation as stepping stones toward the propagation of synthetic genomes.

This achievement will allow scientists to not only read, but also write, genetic code. Dr. Patrinos described a strategy of producing cassette-based combinatorial genomes at a scale of thousands to millions of genomes per day. These would then be screened for their ability to produce compounds that could be used as substitutes for petrochemicals and as designer fuels with advantageous properties. Synthetic genomics may yield microorganisms with novel capabilities, photosynthetic organisms able to generate valuable products directly from CO2, biological systems that increase recovery rates of subsurface hydrocarbons, or advanced plant feedstocks.

Dr. Patrinos revealed that Synthetic Genomics plans to demonstrate proof-of-principle for the creation of a synthetic genome within the next few months.

Pretreatment Releases Sugar Content

Badal Saha, lead scientist at the fermentation biotechnology research unit of the USDA’s Agricultural Research Service (ARS), began his talk with a status report on the fuel ethanol industry. He described the production of ethanol from corn as a mature technology, with U.S. ethanol production reaching nine billion gallons, or about 4.2% of gasoline usage in 2008.

Almost all of this derives from corn, with one bushel of corn yielding about 2.7 gallons of ethanol and about 28% of the U.S. corn crop going toward ethanol production. Even if all the corn grain available were converted to ethanol, however, it would meet only 15–18% of current transportation fuel needs.

Alternative feedstocks are needed to boost ethanol production, Saha said, and the 1.3 billion tons of biomass available in the U.S. would be sufficient to produce the total amount of oil the country imports each year. Advanced biofuels can be derived from lignocellulosic feedstocks, such as agricultural waste (e.g., corn stover, wheat straw, rice hulls), agricultural processing byproducts (e.g., corn fiber or sugar cane bagasse), forestry and wood processing waste, the paper portion of municipal solid waste, or dedicated energy crops such as switchgrass. The main challenge in converting lignocellulosic biomass to biofuel is breaking down the cellulose, hemicellulose, and lignin components to their basic sugars.

A variety of pretreatment strategies have been devised, some of which can disrupt the lignin structure and solubilize the cell wall. Saha described a method of extracting sugar from hemicellulose, which comprises 35% of corn fiber and is made up of 70% carbohydrates.

In this method, pretreatment of corn fiber in a dilute acid solution at moderate temperature is followed by enzymatic saccharification of cellulose, yielding up to 100% of the sugar content of the hemicellulose without generating fermentation inhibitors. With this strategy, saccharification and fermentation are combined in a single process. Saha described similar success applying this strategy to other feedstocks including wheat straw, barley straw, and rice hulls. Technological challenges remain, such as the need for more efficient enzymes for saccharification, new microbes that can ferment multiple sugars, better integration of process steps, and improved methods for recovery of dilute ethanol.

Stephen Hughes, Ph.D., research molecular biologist at the USDA-ARS, described an automated process for high-throughput transformation (with bacterial xylose isomerase and xylose kinase genes), mutagenesis, and screening of yeast to select for fast-growing strains optimized for anaerobic growth on xylose.

A key advantage of using yeast for cellulosic ethanol production is their ability to work over a broad temperature (<44oC) and pH (3.0–8.0) range to produce large amounts of sugar. GMAX-L is a genetically engineered yeast strain able to convert both xylose and glucose to ethanol. It produces 10–15% more ethanol than a strain that utilizes glucose alone.

Dr. Hughes also reported ongoing work to achieve stable expression of a biocatalyst in yeast, which enables the fungi to produce biodiesel after ethanol production has completed. “Ethanol alone is not profitable; valuable coproducts will make biorefineries sustainable,” he concluded, explaining that advanced biorefineries would be able to use engineered yeast such as GMAX for simultaneous production of ethanol, alternative biofuels, plastics, chemicals, and animal feed.

Algae is a viable feedstock for first-generation biodiesel and ethanol production plants, and is a promising resource for producing aviation fuels and biocrude for biogasoline, said Will Thurmond, president of Emerging Markets Online.

“The U.S. and Europe cannot produce enough plant feedstocks to meet targets” for biofuel production—even with cellulosic corn—as defined by government mandates, which are largely being driven by a growing demand for energy independence and national security concerns, said Thurmond.

Algae R&D Intensifies

Algae represent one of many available biodiesel feedstocks that can be cost-competitive with fossil fuels, he explained. He described various methods for growing algae in large scale and converting its fats to biodiesel and its sugars to ethanol. These methods include both anaerobic and aerobic fermentation systems, and photo-bioreactor systems that can utilize the CO2 produced by coal-fired power plants or from cellulosic ethanol production, as a carbon source for algae production.

Citing near-term market opportunities for algal fuel in the aviation industry, Thurmond pointed to the first algal fuel tests conducted earlier this year by Continental Airlines and Japan Air. He anticipates commercialization of algal biofuels in 2011–2012 and predicted that “by 2020, algae will become a mainstream commodity for biocrude, ethanol, and renewable diesel fuels.”

Solazyme’s technology for producing renewable oil-based fuels, chemicals, and edible oils is based on a microalgae platform. The company has passed the proof-of-principle stage and is approaching commercial-scale production.

“Algal genomic data is the basis for much of our work,” said Jonathan Wolfson, CEO of Solazyme. He described algae as the original oil producers. They have a strong evolutionary reason to make oil: as aquatic organisms, oil makes them lighter than water, allowing them to float and more readily access sunlight and the CO2 they need for photosynthesis. They are able to convert this chemical energy into oil.

Solazyme has genetically engineered algae to enable the organisms to grow in the dark and to convert biomass into oil through anaerobic fermentation. The company relies on preexisting, industrial, demonstration-scale fermentation infrastructure to test and optimize its process, and has been able to achieve conversion of 70–80% of biomass into oil-based fuel including jet fuel and biodiesel, which has been road-tested for more than a year in an unblended form in unmodified engines.

“The algae we are developing are feedstock-flexible,” said Wolfson. They will produce the same oil whether they are converting sugar cane, switchgrass cellulosics, or waste glycerol. The company plans to market its first products in 2009 to the nutraceuticals and cosmetics industries, and is also pursuing production of edible oils with lower saturated fat content.