Catalysts of Efficiency

Genencor shares an inside view of the ethanol process, with a focus on optimizing enzyme use.
By Susanne Retka Schill | February 04, 2009
When times were flush in the ethanol industry, Genencor technical staff noted that ethanol plant managers were concentrating their efforts on maximizing throughput. Now in response to the economic downturn, they are seeing more emphasis on maximizing yields. Helping those ethanol plants achieve production goals is what Genencor, a division of Danisco, sees as its role as an enzyme provider.

"Our technical sales staff can really get in there and help ethanol plants get more efficient in how they operate," says Glenn Nedwin, executive vice president of technical enzymes with Genencor. Enzymes comprise a relatively small part of the cost of ethanol production. Corn makes up 65 percent of the cost, natural gas about 15 percent, and enzymes are part of the remaining 20 percent, costing between 3 to 5 cents per gallon. Although seemingly small, improvements to ethanol plant efficiency can add up. Enzyme use refinements can improve efficiency by as little as 1 percent to upwards of 5 percent, in some cases. Given the large volumes produced by today's ethanol plants, a 2 percent increase in ethanol
yield for a 50 MMgy plant amounts to 1 million gallons more ethanol.

"Every single ethanol plant is different," Nedwin says, "the way they turn the valves, the timing they use between the different steps, the volumes they addthis all can be tweaked." Even plants built by the same engineering firm can vary, as the design evolves. "Many ethanol plants don't have a lot of technical analysis to know what's happening at different stageshow much glucose do they produce in this step, how many side reactions do they get, what percent conversion, etc.," Nedwin adds. Genencor's technical sales team can help by collecting samples that can be analyzed by the company's applications team in its laboratories, and by seeing the plant in operation through the eyes of an enzyme specialist. Genencor's technical sales team and experienced plant operators learn from each other as they tweak enzyme protocols to improve efficiency, says Hans Foerster, Genencor's director of marketing for fuel in the Americas. "They have a very good idea of what they're trying to achieve and the limitations of what enzymes can accomplish," he says. Often, ethanol plants are looking for specific ways to eliminate bottlenecks, or figuring out how to handle special conditions. For example, every year enzyme providers hear from plant operators who want to optimize the process so they can use end-of-season bad corn, although using bad corn is never recommended, Foerster says.

The enzyme specialists are also called when a plant wants to adjust its operating goal. Until recently, the emphasis has been on increasing throughput, which is achieved by increasing the level of solids which in turn requires adjusting the enzyme dosing, Foerster says. The more corn that can be processed per hour, the more ethanol can be produced per hourwithin limits. "We have found through experience that there is some level of solids at which a plant operates most efficiently," he says. "We can push beyond that for a gain in throughput, but we'll get less yield." With current economic constraints, however, ethanol plants are now looking to maximize ethanol yields. The Genencor technical sales team works with plant operators to achieve a plant's goals. "It's very much an individual plant prescription," Foerster says.

This summer, Genencor will boost its capacity to help ethanol plants solve process issues and train new plant employees when it completes its Center of Excellence, which is being built near Genencor's manufacturing facility in Cedar Rapids, Iowa. The center includes a pilot plant, additional analytical capabilities and space for group training. "We'll have a space that will allow us to collaborate with customers on specific projects in our lab," Foerster explains. "In most ethanol plants, the laboratory is a very busy place, and tends to be a very constrained space."


In the ethanol production process milled grain is slurried with water and a thermostable alpha amylase enzyme. The slurry is cooked to 221 to 302 degrees Fahrenheit to gelatinize and liquefy the starch in the liquefaction process. The resulting mash is cooled and a secondary enzyme, glucoamylase, is added to convert the liquefied starch to fermentable sugars (glucose) in the saccharification stage. Yeast is then added to the mash to ferment the sugars to ethanol and carbon dioxide. In addition to alpha amylase and glucoamylase, protease can be added to improve the fermentation process, and phytase, a newer enzyme, can be added in the liquefaction stage to enhance the performance of thermostable alpha amylase, or in the yeast fermentation process
SOURCE: GENENCOR

The Center of Excellence will also house a second applications team, in addition to the one at the Beloit, Wis., manufacturing site. Scientists in the applications team back up the technical sales team, analyzing samples gathered at ethanol plants, and creating a link between the team working directly with ethanol plants and the research and development division that's working on new enzymes.

Enzyme Enhancements
Genencor continues to develop new enzymes so it can respond to customers' needs. "Ethanol plants are always looking to reduce manufacturing costs," says Jay Shetty, research fellow in Genencor's applications/technical services division. "To increase efficiency and reduce manufacturing costs you need some additional enzymes." The company has developed a protease enzyme, marketed as Fermgen, which matches the pH environment of the fermentor and increases alcohol yield. It improves fermentation efficiency by breaking down a protein in corn to generate free amino nitrogen a yeast nutrient that boosts yeast action. Protease also releases bound starch molecules, which without the enzyme treatment remain unfermentable and pass through into the distillers grains.

While proteases are gaining acceptance in the industry, a second auxiliary enzyme, phytase, is newer and less widely used, Foerster says. Phytase is added during liquefaction to improve the function of the alpha amylase and glucoamylase and increase ethanol yields. Phytase also improves the feed characteristics of the distillers grains. Genencor's animal nutrition division also includes phytase with other ingredients in an additive to improve distillers grains performance in swine. Genencor's research and development team is working on other enzymes to improve the feed coproduct from the ethanol process, Foerster adds, tapping into the company's capacity to do feeding trials on poultry and swine.

Genencor has developed enzyme cocktails for the emerging cellulosic industry, one is marketed as Accellerase, and the other is Stargen, an enzyme blend for simultaneous saccharification and fermentation with the cook stage eliminated in the corn ethanol process. The required retrofits have somewhat dampened adoption of the cold cook enzymes in the U.S., Foerster says, but it's a different story internationally. "We've had great success with Stargen on noncorn substrates outside of the U.S. where energy prices tend to be higher." In addition to reducing energy costs by eliminating the cook stage, Stargen helps to avoid the high viscosity issues associated with small grains.

Genencor recently extended its cooperative research agreement with scientists at USDA's Eastern Region Research Center to develop enzymes for processing winter barley into ethanol. Enzymes have been developed to address the high-beta glucan content and increase ethanol yields from barley. The barley enzymes are expected to help develop the ethanol industry in the South, where winter barley wouldn't compete with summer food crops. The ethanol yields per acre from barley would be comparable with corn produced in the South.

Unlike corn ethanol, which has two main enzymes plus a handful of auxiliary enzymes, the cellulosic process will require at least six cellulase enzymes that are designed to match the pretreatment and fermentation processes. Genencor received a U.S. EPA grant in 2000, when the cost of enzymes was considered a major hurdle to clear in developing a cost effective cellulosic ethanol process. "We brought the cost of enzymes down 30-fold," Nedwin says. With current enzymes priced between 30 to 50 cents per gallon of ethanol, pretreatment is now the most costly step. "The enzyme price needs to go lower," he adds, with an ultimate goal of about 10 cents per gallon of ethanol produced. While that work continues, Genencor has released its Accellerase line of enzymes which cellulosic ethanol developers are using to test pretreatment and fermentation technologies. The company anticipates continued developments in the Accellerase line of its merchant enzyme business, while it embarks on its own cellulosic ethanol process venture in collaboration with DuPont. DuPont Danisco Cellulosic Ethanol LLC broke ground last fall on a pilot plant in Lenore, Tenn., in a joint venture with Genera Energy LLC, a company formed by the University of Tennessee's Research Foundation. DDCE is working to optimize Genencor's Accellerase line of enzymes, matching them to the biomass pretreatment and planned fermentation process. DDCE has licensed the dilute ammonia pretreatment process developed at Michigan State University and the bacterial fermentation process using Zymomonus mobilis developed by the National Renewable Energy Laboratory. With construction proceeding quickly, the project is gearing up to move from the bench scale to pilot scale and planning for commercialization, says Jack Huttner, vice president of commercial and public affairs for DDCE.

Susanne Retka Schill is an Ethanol Producer Magazine staff writer. Reach her at sretkaschill@bbiinternational.com or (701) 738-4922.