New Pathways for Stover

Innovation in stover utilization targets feed, sugars and coproduct credits, building markets beyond cellulosic ethanol use. In-depth reporting in the November EPM.
By Ann Bailey | October 18, 2016

Building a robust biomass supply chain for the future will require multiple end users. Innovative companies are utilizing stover with new projects in the Midwest and Canada that have the potential to tap into new markets for livestock feed, power and renewable biochemicals. 

London, Ontario-based Comet Biorefining Inc. plans to build a commercial-scale cellulosic sugar plant in TransAlta’s Bluewater Energy Park in Sarnia, Ontario. It will use its patented process to convert corn stover and wheat straw into high-purity dextrose sugars that can be used by biofuel and bioproducts manufacturers for value-added end products. Besides building, owning and operating its own plants, Comet Biorefining plans to strategically license its technology to select partners worldwide to meet the growing demands for biobased products, the company says.

The 60 million pounds-per-year (27,000 tons) dextrose plant is expected to be operational in 2018, says Andrew Richard, founder. The company will buy the corn stover and wheat straw from area producers. “In general, this is an excellent region where the plant will be located. There is plentiful feedstock within close distance to the plant. There’s a tremendous amount of infrastructure, not just on the TransAlta site, but in Sarnia, in general,” Richard says. Construction of the first-of-its-kind plant represents a key step toward large-scale commercialization of its cellulosic sugar business, Richard says. “It highlights the important role our technology plays in the value chain, helping to drive the bioeconomy and reduce greenhouse gas emissions.”

“This facility for us is our first commercial facility and it is an essential step in our development, in our commercialization path to show significant amounts of dextrose being utilized by our customers,” Richard says.  “We have a very strong relationship with our feedstock partners, local cooperatives that have been formed to supply the plant and so we’re pleased with our region and we’re pleased with our partners.”

Earlier this year, Comet announced an offtake agreement with BioAmber to supply dextrose for bio-succinic acid production, giving BioAmber certain exclusive rights in the fields of succinic acid, BDO (1,4-butanediol) and THF (tetrahydrofuran).

Enhancing Stover
Several hundred miles south, Ag Ventures Alliance in Mason City, Iowa, and Cellulose Sciences International in Madison, Wisconsin, formed Stover Ventures to commercialize its process to turn corn stover into nutritious, palatable dairy and beef cattle feed.

Rajai Atalla, a chemist and cellulose researcher who founded Cellulose Sciences International, initially developed a process to pretreat corn stover for ethanol production. Though, he believed—and still believes—in the effectiveness of the pretreatment for cellulosic ethanol, he was unable to convince established ethanol companies to adopt the technology. After attending a workshop on start-up companies in which the speaker advised pivoting, if marketing to the original target industry was unsuccessful, Atalla refocused his efforts on using his pretreatment process to convert corn stover into cattle feed.

“We treated some corn stover and sent it off to one of the animal nutrition laboratories and they were amazed at the dramatically increased digestibility,” Atalla says. Cellulose Sciences’ patented process occurs at room temperature and ambient pressure. “We treat it with sodium hydroxide dissolved in a cosolvent of ethanol and water. If you have the right proportions, you are able to open up the structure of the cellulose so it is much more accessible to the enzymes and, at the same time, you’re able to extract the inhibitors,” Atalla says. “If you remove the inhibitors, it is much easier for the cellulases and xylanases to convert the polysaccharides to glucose and xylose,” Atalla says, and at an increased rate.

In the process, corn stover is shredded to an average size of about one-half inch. The pretreatment process is unique because it avoids thermal degradation of the cellulose, and the conversion to glucose and xylose requires far less time than the four or five days needed for high-temperature, pretreated corn stover. “If we’re dealing with pure cellulose, the pretreatment is complete in 10 to 15 minutes. If we’re dealing with biomass, depending on the biomass, anywhere between 30 and 60 minutes is all it takes. And when we apply the enzymes, we get complete conversion to glucose and xylose, in about 30 to 40 hours.

“Raj has developed a pretty innovative way to treat forage fiber,” says David Combs, dairy scientist in the University of Wisconsin Department of Dairy Science in Madison. The additional step of extracting compounds solubilized by sodium hydroxide to remove them greatly enhances the digestibility of the forage, once it has dried, says Combs, whose work specializes in ruminant nutrition. “You take a product that had digestibility of around 40 percent—60 percent of the fiber that a cows eats, she can’t do anything with it and 40 percent she can. With this process you can increase that digestibility to 75 to 80 percent.” 

The increase in the corn stover’s digestibility puts the feed on par with another fiber supplement, Combs says. “Raj’s treatment process on paper looks to be as digestible as soy hulls and it actually can be produced at a lower cost than what soy hulls cost producers.” Combs completed several feeding studies in December 2015, generating a lot of interest from other dairy scientists and farmers, he says. Further studies may be done with beef cattle. Substituting pretreated corn stover for corn in a majority of beef cattle’s ration could substantially reduce the cost of feeding and also reduce the amount of stover on cropland, Combs says.

Cellulose Sciences International is partnering with Ag Venture Alliance to build a demonstration plant that will allow expanded feeding studies. The alliance, a Mason City, Iowa-based cooperative supporting value-added agriculture, has contributed $500,000 to the Cellulose Sciences project. Most of the alliance’s 635 farmer members live in corn areas of southern Minnesota and northern Iowa where studies have shown removing some of the stover can increase yields. “Farmers, especially ones growing continuous corn, have too much stover left on the fields,” says Jude Conway, Ag Ventures executive director.

Minnesota’s Agricultural Utilization and Research Institute also provided some financial support to Cellulose Sciences’ project. The project fits perfectly with one of AURI’s goals, which is adding value to Minnesota’s agricultural commodities, says Al Doering, AURI senior scientist and a farmer. “What excited AURI is Cellulose Sciences offered a new technology. It didn’t require high pressure to process the stover and the results they saw in the increase in energy value after the treatment, especially when used as a feedstock for ruminants, were incredible,” Doering says.  “It’s a pretty amazing technology. Feeding corn stover or corn stalks to livestock is nothing new, what’s so incredible is the increase in energy availability out of those corn stalks. That’s really where the value comes.”

Ag Ventures Alliance plans to hold informational meetings and raise money this winter and break ground on a demonstration plant next spring. The cooperative has selected a site for the plant and is working with an engineering firm, Conway says. 

Low-Carbon Fuel
A third effort to utilize corn stover is targeting the carbon reduction benefits from using the stover as a biomass fuel source for power plants. Last winter, California-based Trestle Energy LLC received a favorable carbon intensity (CI) rating from the California Air Resources Board for its pathway that would shave 18 points off an ethanol plant’s CI rating, according to the CARB staff summary. The company has received favorable CI ratings under the British Columbia Low Carbon Fuel Standard and has a pathway pending with the U.S. EPA.

James Rhodes, co-founder and president of Trestle Energy says the approach creates a new coproduct credit from using corn stover for electric generation, either at an ethanol plant with biomass boilers, or at a partnering utility cofiring biomass with coal. The process allows both sides of the supply chain to reap emissions reduction benefits, Rhodes says. “By making pellets a coproduct of ethanol, the financial benefits of low-carbon fuels can make biomass power a cost-effective option for coal plants to use in meeting their own compliance requirements.”

Data for the life-cycle analysis of the pathway was collected in a demonstration project conducted in 2012 and 2013 with Iowa-based Golden Grain Energy and Cedar Falls Utilities, with the help of Larksen LLC, which works with utilities for biomass supplies. The utility, Rhodes explained, has been evaluating the possible use of biomass in one of its coal-fired boilers for several years. The life-cycle analysis used for the CARB CI score took into consideration the additional use of farm equipment for stover removal, additional inputs to offset nutrients removed and feedstock transportation, among other factors. The biggest CI reduction was the result of avoided emissions from using the crop residues.
Coproduct credits are common in life-cycle analyses, Rhodes says. A common coproduct credit in biodiesel CI pathways, for example, comes from the feed produced at the soybean mill. Another example would be California crude oil that is produced with enhanced oil recovery using steam. The production of that steam includes an electricity coproduct that is credited to the fuel. Rhodes pointed out applying the coproduct credit would make Midwestern corn ethanol competitive with Brazilian sugarcane ethanol, where the coproduct credit for generating electricity from bagasse is a big part of the fuel’s low carbon intensity score.

Rhodes is optimistic about the next step. “We have a whole series of test burning opportunities that could launch for 2017 harvest,” he says. “Since we received the approval, we’ve been speaking with utilities, mainly in the western half of the Midwest, looking at opportunities to commercialize.”

Author: Ann Bailey
Associate Editor, Ethanol Producer Magazine