Sweet-Spot Search

FROM THE JULY ISSUE: Cellulose molecules are more complex than starch molecules, so employing the proper enzymes in cellulosic ethanol production is vital. Optimization research is ongoing.
By Tim Albrecht | June 26, 2018

Cellulosic ethanol production has seen its share of hurdles as it has gotten off the ground. Creating fermentable sugar from biomass feedstocks is tougher than creating that sugar in corn for ethanol, but that’s where enzymes come in. Researchers from a variety of companies have continuously been developing new enzymes that best suit the industry, says Jan Koninckx, global business director for advanced biofuels at DuPont.

“We continue to work on new enzymes,” Koninckx says. “We’re a market-back science company in the sense that we look for market need and focus our research efforts there.”

Enzymes in the cellulosic sector have come a long way since the early stages of the industry. Researchers have been able to reduce the cost of enzyme production dramatically and delve into new ways to tailor products to producers’ processes, Koninckx says.

Current Market Needs
Historically, the price of enzymes for cellulosic ethanol production have been high, inhibiting large-scale production. “When we started in 2001, enzyme cost was higher than a gallon of gasoline,” says Thomas Schroder, vice president of commercial biorefining at Novozymes. “Since then, we’ve taken down cost more than 15 times. The cost has come down to a level to where the enzyme is no longer inhibiting economically deploying the technology. Right now, enzyme cost is maybe between the fourth- or sixth-largest component of production.”

Novozymes has been producing enzymes for the cellulosic ethanol industry since 2009. The company has developed two more generations of its original Cellic product. The newest version, Cellic CTec 3, launched in 2012.

When Novozymes started, it was focused on creating a product that could apply to as many processes as possible, Schroder says. “Those first-generation products were products that were cutting across different types of substrates and processes. So, you could say it was a silver bullet that could be used for any application.”

DuPont currently offers two product lines of enzymes to the cellulosic sector. One focuses on corn fiber, the other on cellulosic ethanol from biomass, such as corn stover, wheat straw or sugarcane bagasse, Koninckx says.

“In the biomass product line, we don’t have a generally available product line, like we do in the corn fiber-related line,” he says. “In the biomass product line, we typically work one-on-one with the customer. We fine-tune and customize those kinds of products.”

Koninckx says the growth of the cellulosic ethanol industry will generate more research into the functionality of enzymes, driving the cost down even further. “If you go back say 10 years ago, the cost of enzymes has come down tremendously, but they’re still high compared to the cost of enzymes in grain ethanol,” Koninckx says. “Grain ethanol enzymes were costly at the beginning as well, so I believe the cost will come down over time.”

Cost is crucial, says Delayne Johnson, CEO of Quad County Corn Processors in Galva, Iowa, which produces cellulosic ethanol from corn fiber. “We’re looking for the most cost-effective enzyme. That could be an enzyme that either has very good efficiency and conversion, one that has low cost, or a combination of the two.”

For Steve Roe, CEO of Little Sioux Corn Processors in Marcus, Iowa, finding the right enzyme is about finding the right conversion rate. LSCP produces cellulosic ethanol using corn fiber. Roe says the plant isn’t loyal to one specific company and has trialed a handful of products since 2015.

“We’re going to look for the highest D3 conversion, something that is relatively stable as far as storage ability, something that at least shows some promise toward distillers corn oil production and gas reduction in the dryer,” Roe says. “Between the three products we trialed, we couldn’t see any difference in corn oil production or spikes in gas usage, so we think they’re fairly equal. But if we take the cellulase out, our gas usage goes up and our corn oil yield goes down, so we know that it helps.”
LSCP began producing cellulosic ethanol in October of 2017 after a couple years of enzyme experimentation. The plant will be switching to a DuPont enzyme as soon as the appropriate addendum to its D3 pathway is approved by the U.S. EPA.

Tailored Enzymes
With new enzymes being produced and the ability to customize them to specific processes, the overall cost of cellulosic ethanol production has gone down, making it a more profitable market, Koninckx says.

Customization of enzymes for cellulosic ethanol came along naturally as researchers delved into how to break down cellulose and hemicellulose faster. That breakdown to create fermentable sugars is harder in cellulosic biomass than it is in grain because biomass is more complex, Koninckx says. In corn-ethanol production, the starch in the grain is converted to sugar, but in cellulosic ethanol production, it’s the cellulose and hemicellulose in the biomass that is converted to sugar. “Although starch molecules and cellulose molecules are chemically similar, it is chemically easier to convert starch molecules, versus cellulose or hemicellulose molecules, into sugar molecules,” Koninckx says.
He compares it to a human digestive system. It’s easy for humans to convert starch, such as a bagel, to sugar, which is similar to starch in corn-ethanol production. But a human digestive system cannot meaningfully extract energy out of raw biomass rich in cellulose, such as grass.

“These enzymes function within a production process and those production processes are different based on different acidities, temperatures and so on,” Koninckx says. “A certain enzyme may be customized for a certain set of conditions. That’s not any different than what you’d find in very many other enzyme applications. Enzymes are slightly modified to work best under a set of conditions, such as high-temperature liquefaction or low-temperature liquefaction in corn ethanol production. It’s the same concept in biomass.”

Catering to a specific plant’s process and feedstock generates more value, Schroder says. “If you have a very broad spectrum of a multicomponent cocktail of enzymes, and if you have to keep reaching all these processes and feedstocks, that multicomponent becomes wider and wider, and needs to do more things,” Schroder says. “This sets a limit to a one size-fits-all enzyme solution. That also means that a producer’s cost picture could go up. So, it was a way to balance efficiency of cost.”

Novozymes works together with its customers to ensure the “process speaks to the enzymes in the most optimized manner,” Schroder says. He adds that, together, Novozymes and its customers further improve hydrolysis, pH, temperature profiles and contamination control.

“From our customizations you can see that’s where a lot of value is being harvested in the combination of the hardware and the software, so to say,” Schroder says.

Looking Forward
Further enzyme improvement could make the cellulosic ethanol production process more cost-effective. The goal is to make enzymes more efficient, Schroder says. “It’s about ensuring you can get the lowest production cost per liter or gallon of ethanol produced. So, you will see our enzyme getting more potent, being able to do more. In the long term, say 20 years from now, when someone builds a second-generation plant, a producer will probably need less enzymes, because the enzymes are simply able to do more.

“It’s a multicomponent cocktail of activities that needs to do different types of jobs, so what we see down the road is that these enzymes get more efficient and as they work closer with the process, the enzyme use cost will come down and efficiency will go up,” he adds. “You can also use the potency of the enzymes to lower the enzyme dosing. It all depends on the value of your ethanol and the cost of raw materials that go in. Basically, it’s about finding the sweet spot for the producers’ specific process.”
Koninckx agrees. “I envision enzymes becoming more and more efficient in their functionality, so you can use less and less enzymes to get the same effect, or the same amount to get more effect,” he says. “Just like with grain ethanol, enzymes will become less of an important part of the cost equation. It won’t be done overnight, though.”

Author: Tim Albrecht
Associate Editor, Ethanol Producer Magazine