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UC Riverside CELF biomass pretreatment technology could cut cellulosic biofuel production cost by about 30%

Yields of glucose, xylose, and arabinose from CELF- and dilute acid-pretreated corn stover solid. “D” equals day. Source: UCR. Click to enlarge.

Researchers at the University of California, Riverside led by Professor Charles Wyman, the Ford Motor Company Chair in Environmental Engineering, have developed a novel biomass pretreatment called co-solvent-enhanced lignocellulosic fractionation (CELF) to reduce enzyme costs significantly for high sugar yields from hemicellulose and cellulose—an essential development for the low-cost conversion of biomass to fuels.

As partners in the BioEnergy Science Center (BESC), the team from the Bourns College of Engineering Department of Chemical and Environmental Engineering and Center for Environmental Research and Technology (CE-CERT) have shown that CELF could eliminate about 90% of the enzymes needed for biological conversion of lignocellulosic biomass to fuels compared to prior practice. This development could mean reducing enzyme costs from about $1 per gallon of ethanol to about 10 cents or less, with an overall reduction in the cost of the production of cellulosic biofuels of 30% or more.

The findings by Wyman’s research group were outlined in a just-published paper in the journal ChemSusChem. Co-authors with Wyman are: Thanh Yen Nguyen, Charles M. Cai, and Rajeev Kumar, all of whom are students or research engineers in Wyman’s lab.

CELF employs THF miscible with aqueous dilute acid to obtain up to 95 % theoretical yield of glucose, xylose, and arabinose from corn stover even if coupled with enzymatic hydrolysis at only 2 mgenzyme gglucan−1. The unusually high saccharification with such low enzyme loadings can be attributed to a very high lignin removal, which is supported by compositional analysis, fractal kinetic modeling, and SEM imaging. Subsequently, nearly pure lignin product can be precipitated by the evaporation of volatile THF for recovery and recycling. Simultaneous saccharification and fermentation of CELF-pretreated solids with low enzyme loadings and Saccharomyces cerevisiae produced twice as much ethanol as that from dilute-acid-pretreated solids if both were optimized for corn stover.

—Nguyen et al.

Diagram of a proposed biomass conversion process that integrates CELF pretreatment with Simultaneous Saccharification Fermentation (SSF) to produce ethanol. Source: UCR. Click to enlarge.

Research by the Wyman team focuses on turning lignocellulosic biomass into liquid transportation fuels. Lignocellulosic biomass is attractive because it is sustainable and abundant and inexpensive compared to oil. For example, lignocellulosic biomass costing about $60 a dry ton is equivalent in unit energy costs to oil at about $20 barrel. (Oil is currently selling for about $55 a barrel but has hovered around the $100 per barrel mark in recent years.) The challenge is to lower the cost of processing low cost biomass sources into fuels.

Biological processes favored for making liquid biofuels convert the hemicellulose and cellulose in biomass into sugars that can in turn be fermented into biofuels. However, the complex structure of lignocellulosic biomass makes it difficult for enzymes to release these sugars, and a pretreatment step using heat and chemicals is needed to reduce this recalcitrance enough to realize the high yields vital to economic success.

The lignin left in biomass after most pretreatments presents a particular problem by impeding enzyme access to hemicellulose and cellulose, thereby hurting product yields and requiring more enzyme at a substantial cost.

CELF, the pretreatment developed at UC Riverside, addresses those problems. In the ChemSusChem paper, the UC Riverside researchers outline laboratory results in which they compared the total achievable combined sugar yields between CELF pretreatment and dilute acid pretreatment, a current leading strategy, coupled with subsequent enzymatic hydrolysis in three timeframes with three levels of enzymes.

  • Using the dilute acid method, the sugar yield was only about 70% of the maximum possible after 14 days when two milligrams of enzymes were used. That percentage increased to about 85% in 14 days when 15 milligrams of enzymes were added.

  • By contrast, CELF pretreatment increased sugar yields to about 95% of the maximum possible regardless of whether two milligrams, five milligrams, or 15 milligrams of enzymes were added. Furthermore, the time required to reach these high yields dropped to five days when five milligrams of enzyme were used and two days when 15 milligrams of enzyme were used.

In addition, CELF is capable of dissolving and extracting up to 90% of the lignin in corn stover and even more for woody biomass. After pretreatment and enzymes release of the sugars from hemicellulose and cellulose, previous process strategies have focused on burning the residual lignin, which is a low value proposition. However, lignin has promise as a resource from which to make additional high value chemicals and fuels once it is extracted and depolymerized with CELF.

These findings are very significant because they establish a new pretreatment process that can dramatically reduce enzyme loadings and costs, thereby improving the competitiveness for biological conversion of lignocellulosic biomass to fuels. Understanding the mechanisms responsible for achieving these intriguing results can also suggest even more powerful paths to improving the economics of converting non-edible biomass into sustainable fuels.

—Charles Wyman

The National Science Foundation contributed to making this project possible through their Graduate Research Fellowship Program. Initial application of CELF to biological conversion was supported by the UC Riverside Research and Economic Development Office of Technology Commercialization and the University of California Transportation Center.

The UC Riverside Office of Technology Commercialization has worked with the inventors to file a patent on the invention. CELF is now exclusively licensed by partners from CogniTek in Northbrook, Ill., who will be working with Cai and Wyman to launch a new spin-off company, MG Fuels, to commercialize the technology.

The BioEnergy Science Center is a US Department of Energy Bioenergy Research Center focused on enhancing science and technology to reduce the cost of biomass conversion through support by the Office of Biological and Environmental Research in the Department of Energy Office of Science.


  • Nguyen, T. Y., Cai, C. M., Kumar, R. and Wyman, C. E. (2015), “Co-solvent Pretreatment Reduces Costly Enzyme Requirements for High Sugar and Ethanol Yields from Lignocellulosic Biomass” ChemSusChem doi: 10.1002/cssc.201403045



The fractionation of lignin is excellent.  It is a source of phenols which have a multitude of uses.

I'm not finding anything on THF inhibition of yeast in a quick search.  There's also the issue of wastewater treatment and recycle of CaSO4 in the case where there's no market for e.g. drywall.  Not bad, though.  If the sulfate could be recycled to H2SO4 by electrolysis and ion exchange (swapping 2H+ for Ca++) it would close that loop.

I would love to see something about the process energy requirements.  This looks like something that could be done entirely with low-pressure steam, tapped off-peak from a powerplant.

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