Unraveling the Science behind Biomass Breakdown

Researchers at ORNL and UCR uncover the chemical reaction that helps break down biomass for biofuel

An illustration that demonstrates how tetrahydrofuran (orange) and water (blue) separate on the surface of cellulose (green), thus facilitating its breakdown.

Lignocellulosic biomass—plant matter such as corn residues, grasses, straws, and wood chips—is an abundant and sustainable waste product ideal for the production of renewable fuels and chemicals. But breaking down biomass, through a process known as pretreatment, is one of the most expensive and energy-intensive steps in its conversion to renewable products.

In research published recently in theJournal of the American Chemical Society, a team from the U.S. Department of Energy’s (DOE’s)Oak Ridge National Laboratory(ORNL) and the University of California, Riverside (UCR) has now discovered new mechanisms that assist in biomass breakdown during aqueous pretreatment.

A group led by Jeremy Smith, a University of Tennessee (UT)–ORNL Governor’s Chair and the director of the UT–ORNL Center for Molecular Biophysics, paired computer simulations with experiments to reveal a how the unique interactions of water with an added co-solvent during pretreatment enhances biomass breakdown beyond what was possible with water alone. This new mechanism highlights the effectiveness of a novel pretreatment process called CELF, which was recently invented by Charles Cai andCharles Wyman at UCR’s Center for Environmental Research and Technology (CE-CERT).

CELF, also known as Co-solvent Enhanced Lignocellulose Fractionation, involves the addition of the co-solvent tetrahydrofuran (THF) to augment aqueous pretreatment of biomass. In particular, CELF has demonstrated exceptional ability for dissolving plant lignin—the “glue” in plant cell walls—that resists breakdown and prevents access to other cell wall components during pretreatment. This study reveals a new interaction of the co-solvents in CELF with cellulose—the main structural component of plant cell walls—to directly enhance its breakdown or solubilization. The solubilization of cellulose is essential for its conversion into second generation biofuels such as cellulosic ethanol or other advanced biofuels that do not compete with food resources.

Lead author Barmak Mostofian, a postdoctoral researcher on Smith’s ORNL team, created models of up to 330,000 atoms and ran simulations on ORNL’s flagship supercomputer—the Cray XK7 Titan—earlier this year. They found that the THF–water solvent solution separates on distinct regions of the cellulose fiber. During this separation, THF preferentially binds to the hydrophobic or ‘water repelling’ regions of the cellulose, and water preferentially binds to the hydrophilic or ‘water attracting’ regions. This separation potentially increases the hydrolysis, or water-mediated breakdown, of cellulose. Understanding more about the process of breaking down cellulose can enable more rapid improvements in current pretreatment methods and lead to new solvents that work more efficiently.

“The real breakthrough needed to realize economic processing of stubborn biomass depends on a pretreatment process’ ability to efficiently solubilize the major biomass components such as lignin and cellulose. This way we can recover more sugars and lignins from plants as high quality precursors for their conversion into renewable fuels and chemicals. The results of this study establish our CELF technology as a leading pretreatment process,” said Charles Cai, assistant research engineer at CE-CERT and adjunct professor in UCR’s Bourns College of Engineering.