Raw Biomass can be Turned into Biofuels by a Two-Step Chemical Process

The key to the new process is the first step, in which cellulose is converted into the "platform" chemical 5-hydroxymethylfurfural (HMF), from which a variety of valuable commodity chemicals can be made.

Raines and graduate student Joseph Binder, a doctoral candidate in the chemistry department, developed a unique solvent system that makes this conversion possible. The special mix of solvents and additives, for which a patent is pending, has an extraordinary capacity to dissolve cellulose, the long chains of energy-rich sugar molecules found in plant material. Because cellulose is one of the most abundant organic substances on the planet, it is widely seen as a promising alternative to fossil fuels. This solvent system can dissolve cotton balls, which are pure cellulose and it's a simple system—not corrosive, dangerous, expensive or stinky.

This approach simultaneously bypasses another vexing problem: lignin, the glue that holds plant cell walls together. Often described as intractable, lignin molecules act like a cage protecting the cellulose they surround. However, Raines and Binder used chemicals small enough to slip between the lignin molecules, where they work to dissolve the cellulose, cleave it into its component pieces and then convert those pieces into HMF.

In step two, Raines and Binder subsequently converted HMF into the promising biofuel 2,5-dimethylfuran (DMF). Taken together, the overall yield for this two-step biomass-to-biofuel process was 9 percent, meaning that 9 percent of the cellulose in their corn stover samples was ultimately converted into biofuel.

DMF has the same energy content as gasoline, doesn't mix with water and is compatible with the existing liquid transportation fuel infrastructure. It has already been used as a gasoline additive.

In addition to corn stover, Raines and Binder have tested their method using pine sawdust, and they're looking for more samples to try out. "Our process is so general I think we can make DMF or HMF out of any type of biomass," he says.