Researchers at the University of Wisconsin-Madison led by Dr. James Dumesic have developed a streamlined process for converting lignocellulosic biomass into chemicals or liquid transportation fuel. Using gamma-valerolactone (GVL) as a solvent, they converted the cellulosic fraction of lignocellulosic biomass into levulinic acid (LA), while at the same conditions converting the hemicellulose fraction into furfural. This is followed by conversion to GVL; essentially, the team is leveraging GVL to produce GVL, which has potential as an inexpensive, yet energy-dense, “drop-in” biofuel. (Earlier post.)
This process allows for the conversion of hemicellulose and cellulose simultaneously in a single reactor, thus eliminating costly pre-treatment steps to fractionate biomass and simplifying product separation. Pretreatment and extraction or separation steps can account for up to 30% of the total capital cost of a biofuels production plant.
An open-access paper on their work is published in the RSC journal Energy & Environmental Science.
Based on the yields achieved, this process is comparable in the production of fuels with the production of ethanol by fermentation. Additionally, the GVL solubilizes the degradation products typically formed during biomass deconstruction. Thus, the strategy can be implemented using continuous flow reactors without problems associated with the deposition and accumulation of solid residues. The possibility of producing a single product, GVL, from the hemicellulose and cellulose fractions of lignocellulosic biomass, the elimination of pretreatment steps, and the simplification of separation steps should improve the economics for production of chemicals and fuels from biomass.—Alonso et al.
In their process, an open reactor system produces furfural from hemicellulose. Since furfural has a lower boiling point than GVL (b.p. 441 K vs. 481 K), it is continuously removed by distillation. The cellulose is converted to LA, passing through the intermediate formation of hydroxymethylfurfural. The continuous removal of furfural from the reactive liquid minimizes furfural degradation and leads to high yields of furfural (e.g., 80%) from direct conversion of hemicellulose in corn stover. The less reactive cellulose fraction is converted with high yield to LA (e.g., 60%) by increasing the residence time in the reactor.
Furfural, LA, and GVL can be used as chemical intermediates or can be converted to fuel components such as methylfuran, diesel, and butene oligomers.
Alternatively, the team found, a closed batch reactor configuration can simultaneously converts hemicellulose and cellulose to furfural and LA, respectively, and then, without separation, these intermediates can be upgraded catalytically to GVL. Furfural can be converted to furfuryl alcohol in the GVL solvent, followed by conversion over an acid catalyst to produce LA, such that high yields of LA are achieved from both the hemicellulose and cellulose fractions of lignocellulosic biomass, completed by reduction of LA to GVL over a RuSn catalyst.
In general, says Dumesic, levulinic acid, furfural and GVL are all valuable chemicals that have different applications. “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.”
The authors highlighted a number of advantages of using GVL as a solvent:
It eliminates or simplifies separation steps since GVL is a product of the process.
At the reaction conditions, the GVL effectively solubilizes the biomass, thereby eliminating the formation of solid deposits that typically lead to reactor clogging and solids handling problems.
GVL decreases the rate of furfural degradation and increases the rate of cellulose conversion. Thus, furfural can be evaporated from the less volatile GVL solvent at elevated temperatures (e.g., 410 K) without undergoing significant degradation.
The GVL solvent broadens the optimal conditions for the separate processing of hemicellulose and cellulose, such that these conditions overlap, which allows hemicellulose and cellulose to be processed at high yields under the same conditions.
GVL is completely miscible with water, allowing wet biomass to be used in the process.
While the group conducted its research in small batches in the laboratory, Dumesic says the process could scale to a continuous-flow reactor. For 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.
Other authors on the paper include UW–Madison chemical and biological engineering postdoctoral researchers David Martin Alonso and Stephanie Wettstein and graduate students Elif Gurbuz and Max Mellmer. The group received funding for the research from the Great Lakes Bioenergy Research Center at UW–Madison and from the US Defense Advanced Research Projects Agency.
David Martin Alonso, Stephanie G. Wettstein, Max A. Mellmer, Elif I. Gurbuz and James A. Dumesic (2013) Integrated conversion of hemicellulose and cellulose from lignocellulosic biomass. Energy Environ. Sci., 2013, Advance Article doi: 10.1039/C2EE23617F