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Sustainable Energy

Energy Department Backs New Way to Make Diesel from Corn Stalks

A novel chemical pathway could address the high cost of transporting cellulosic materials to make diesel fuel.

Renewables can’t beat coal on cost and performance yet.

Within a year, a pilot plant in Indiana will start converting the stalks and leaves of corn plants into diesel and jet fuel. The plant will use a novel approach involving acid as well as processes borrowed from the oil and chemical industry, which its developers hope will make fuel at prices cheap enough to compete with petroleum.

The plant, which will have the capacity to process about 10 tons of biomass a day—enough for about 800 gallons (3,000 liters) of fuel per day, will be built by Mercurius Biofuels of Ferndale, Washington, with the help of a grant from the U.S. Department of Energy of up to $4.3 million.

Cellulosic biomass—corn stalks and other matter like wood chips and grass—are abundant and require less energy and fertilizer to produce than sugar or corn grain, the main sources of biofuel now. Because of this, the production of cellulosic biomass is cheaper and results in less carbon dioxide emissions.

But so far it’s proved difficult to make fuel economically from these sources (see “Cellulosic Ethanol Inches Forward”). One big problem has been the cost of transporting raw biomass. A solution is to build small biorefineries that are close to the needed feedstocks, but smaller facilities tend to be more expensive per liter of fuel produced.

In Mercurius’s new process, biomass can be converted into a liquid intermediate chemical at small plants located close to sources. That liquid takes up much less volume than the original biomass, making it more economical to ship to a large centralized facility to be converted to fuel.

Mercurius uses acids to break down cellulose and make a chemical called chloromethylfurfural; the process is based on an approach developed by Mark Mascal, a professor of chemistry at the University of California at Davis.

Converting cellulose to this chemical makes more efficient use of the carbon in cellulose than one of the most common approaches to making fuel from cellulose: converting cellulose into sugar and fermenting it to make ethanol. “Fermentation blows out one-third of the carbon as carbon dioxide,” Mascal says. “[Our process] captures all of the available carbon in biomass.”

The chloromethylfurfural, in turn, can be converted into diesel or jet fuel with industrial processes similar to those used in the chemicals industry and at oil refineries. “We have processes that are a lot like petroleum refining processes, so it’s scalable and potentially faster to bring to market,” says CEO Karl Seck.

Using acids can be expensive, so one key to the process is the fact that it will be easy to recycle the acids used. Unlike sugar, the chloromethylfurfural isn’t soluble in water, so it is easy to separate it from the acid so the acid can be used again, Seck says (see “Reinventing Cellulosic Ethanol Production”). He says the process will also be cheaper than using enzymes to break down cellulose, a common approach being developed now.

Other companies and academic groups are developing processes for making biofuels from cellulose. Many of these turn biomass into gases before converting those gases into fuels. In contrast, Mercurius’s approach makes liquids that are cheaper to handle, requiring smaller and cheaper equipment.

The new technology is at an early stage. Each part of the process has been demonstrated, including the final steps of producing diesel and jet fuel that meet specifications for use in vehicles. But everything has only been done at a small scale, and the entire process hasn’t yet been linked together. Some other alternatives are further along.

Kior, for example, uses a catalytic process to break up cellulose to make a sort of crude oil that, as with Mercurius’s technology, can be processed into diesel and other fuels (see “Kior ‘Biocrude’ Plant a Step Toward Advanced Biofuels”).

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