Using a biomass-derived solvent, UW-Madison chemical and biological engineers have streamlined the process for converting lignocellulosic biomass into high-demand chemicals or energy-dense liquid transportation fuel.
Their new method eliminates the need for costly pre-treatment steps that separate hemicellulose and cellulose, two main components of plant biomass that react at different rates. Pretreatment and extraction or separation steps can account for up to 30 percent of the total capital cost of a biofuels production plant.
The “magic potion” that enables the researchers to simultaneously process hemicellulose and cellulose, which have significantly different physical and chemical properties, is gamma-valerolactone, or GVL.
For biomass conversion, GVL is an ideal solvent because it already is a product of the conversion process. “Water is used now, but it leads to low rates and low yields of desired products,” says James Dumesic, the Steenbock professor and Michel Boudart professor of chemical and biological engineering.
GVL broadens the optimal conditions for separately processing hemicellulose and cellulose. As a result, those optimal conditions overlap, enabling Dumesic and his group to process both—with high yields—under the same conditions.
Now, in a single reactor, the researchers can convert hemicellulose to furfural and cellulose to levulinic acid.
In general, says Dumesic, levulinic acid, furfural and GVL are all valuable chemicals that have different applications. In the United States, approximately 300,000 tons of furfural each year are used as solvents and in adhesives and polymers. “And within the bioenergy space, there’s been more interest recently in making commodity chemicals,” he says. “But if you want to make a fuel, GVL is the way to go, because it can be blended as a fuel additive.”
GVL also solubilizes lignins and humins—biomass material that typically clogs the system. As a result, those degradation products move freely through and out of the reactor in a more environmentally friendly process.
And, GVL can mix with water, meaning the researchers’ process works even with biomass that’s wet.
From small batches in the lab, the process could scale to a continuous-flow reactor. Now, the researchers are studying how long they can use GVL in the biomass conversion process before they have to clean it to remove any impurities that have accumulated in it.
Dumesic and his group described the process in a paper published online Nov. 1, 2012, in the journal Energy & Environmental Science. The group received funding for the research from the Great Lakes Bioenergy Research Center at UW-Madison and from U.S. Defense Advanced Research Projects Agency.