Wood Ethanol alongside Corn

by Susanne Retka Schill (Ethanol Producer Magazine) A startup advanced biofuel company is including first-generation corn ethanol plants in its commercialization strategy. Its vision includes regional crop conversion and enabling today's biorefineries to process woody biomass.

Comstock Fuels proposes marrying corn ethanol production to cellulosic biofuels from wood—and not just ethanol. Comstock’s technology introduces a new coproduct they’ve dubbed Bioleum that is similar to vegetable oil and suitable for hydrotreating to renewable diesel or sustainable aviation fuel.

In a recent news release, Comstock CEO Corrado De Gasperis summarized the value proposition: “Woody biomass is a dramatically less expensive and available feedstock and delivers substantial higher revenue from significant higher lifecycle carbon gains, when compared to corn.”

Known historically as a silver mining company, Comstock Inc. pivoted five years ago to acquiring and deploying decarbonization technologies, says Chad Michael Black, director of business development. Two years ago, Comstock acquired David Winsness’ company, Plain Sight Innovations, and all its intellectual property. “Since that time, we have been working with him and our team in the R&D lab in Wausau, Wisconsin, to get these technologies commercially viable.”

Now they’re ready to go public, with Winsness ready to hit the biofuel event speaking circuit and doing this first media interview with Ethanol Producer Magazine.

Process Separation
The challenge for cellulosic biofuel technology developers has been pretreatment and overcoming inhibitors. Many technologies have worked with exotic enzymes to break open the tightly bound lignocellulosic structure, while another approach has been using steam explosion to shatter the structure. Comstock’s technology takes a different approach. “What we do first is separation,” Winsness explains. “Instead of working around the lignin, we remove it. We remove that inhibitor first with our pulping solvent, which allows us to capture all the lignin.”

The process used has been well established for over a century in the pulp and paper industry, but the difference is in the solvent—the secret sauce of the Comstock process, Black says.

Another 50% of a tree, roughly, is comprised of cellulose, Winsness continues. “Cellulose is a glucan molecule, just like starch is a glucan molecule that converts into glucose. We use a slightly different enzyme for cellulose glucans than starch, but we produce an identical sugar. We make C6 sugars,” he says. “We don’t require an exotic enzyme. It’s a cellulase, but it’s not an exotic one that has to get through inhibitors. Then we use a Gen 1 yeast to convert that sugar into ethanol.”

The remaining portion of the tree, the hemicellulose, contains the C5 sugars that have been problematic in other technologies. In Comstock’s process, the hemicellulose is combined with the lignin to be conditioned into the new product trademarked Bioleum.

Comstock’s technology has been developed at its research facility in Wausau, Wisconsin. “We started on the bench, moved up to a 50-gallon reactor and then to a 2,000-gallon reactor, with no change in the chemistry,” Winsness says. “We can do about a half ton of biomass in about three hours. We’re at commercial scale and we have several thousand hours of operation.”

Comstock plans to use the same 2,000-gallon configuration as in the Wausau pilot facility in its first commercial deployments, but feed it continuously, Winsness says. “We use the same digesters used in pulp and paper, but we use a different solvent and operate them differently. So we’re not reengineering, just changing the process and using the same old-fashioned, reliable equipment that’s out there.”

The wood handling also is similar to a paper mill’s process, where wood chips are first washed to remove stones and other debris.

The company touts its technology’s potential to help with reforestation efforts, make use of forest fire reduction material, and give owners of under-utilized forestlands new income streams. Those landowners could sustainably harvest enough feedstock, the Comstock website says, “to decarbonize while producing about 18 barrels of bio crude per acre with our technology.”

Corn Belt Application
Winsness also sees the Comstock process as being well suited for ethanol plants located near woody biomass on the fringes of the Corn Belt, or located near land not well suited for corn. “They started to do that in Minnesota in that grey area between corn acres and wood acres,” Winsness says. Years ago, over 15,000 acres of poplar were planted to supply a paper mill that subsequently closed. “But they proved the concept. They proved there are less desirable acres for corn or other crops that could be fantastic for woody biomass.

Comstock’s business model calls for a corn ethanol plant to add its unit to process woody biomass. The C6 sugars would supplement corn fermentation and the Bioleum bio intermediate would be shipped to a renewable diesel refinery.

New biointermediate rules in the Renewable Fuels Standard announced last year will potentially make a big difference. Winsness pointed out that in the comments on the proposed rule, “everybody in the renewable fuel industry supported it. And it also got 100% support from the oil industry. I’ve never seen that, ever. But now they’re included. They want to buy intermediates. There’s 40 facilities being built or expanding for hydrotreating.”

That explosion in renewable diesel capacity, and an expected increase in sustainable aviation fuel production, is putting pressure on lipid feedstocks, evidenced by the doubling of prices for fats, oils and greases. That, in turn, is stimulating interest in multiple directions, from new soybean crush facilities under construction to new oil-seed winter cover crops being scaled. The RD and SAF developers have reached out to Comstock as well.

Partnerships are beginning to take form, Black says. “We’re in deep negotiations to license this technology around the world with extremely credit worthy counterparts.” He expects announcements to be “coming down the pike in the relatively near future.”

The level of interest in Comstock’s technology was revealed in a January announcement of a $2 million U.S. Department of Energy grant to build a pre-pilot scale system to demonstrate Comstock’s next-generation technology. Comstock’s new pathway involves the fermentation of cellulosic sugars into lipids, reacting the lipids with Bioleum to produce a homogeneous feedstock, and converting that into drop-in renewable fuels. Yields are expected to exceed 80 gallons per dry ton on a gasoline gallon equivalent. READ MORE