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Carbon-Neutral Biofuels Get Closer to Reality with Novel Method to Break Down Lignin

Energy & Environment
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February 7, 2024

Biofuels have long held tremendous promise. But the vision of powering planes and cars with plants has never become a reality. That might all be about the change. A recent study from the University of California, Riverside, revealed a new method to cheaply and easily break down plant material, a critical step that has long stymied the biofuels industry. By incorporating a straightforward, sustainable chemical into the plant pretreatment process, the study demonstrated that next-generation biofuel production could soon be both economically viable and carbon neutral.

For biofuels to disrupt petroleum, the biofuels industry needs to better utilize lignin, a critical component that provides plant cell walls with structure and helps protect them from disease. “Lignin utilization is the gateway to making what you want out of biomass in the most economical and environmentally friendly way possible,” says Charles Cai, Associate Research Professor at UC Riverside. “Designing a process that can better utilize both the lignin and sugars found in biomass is one of the most exciting technical challenges in this field.”

To address this challenge, Cai developed CELF (co-solvent enhanced lignocellulosic fractionation), an innovative biomass pretreatment technology. CELF incorporates tetrahydrofuran (THF) into the pretreatment process, enhancing efficiency and enabling lignin extraction, with the added advantage that THF itself can be derived from biomass sugars.

A groundbreaking paper published in Energy & Environmental Science outlines the economic and environmental advantages of a CELF biorefinery over conventional petroleum-based fuels and earlier biofuel production methods. This collaborative effort involved researchers from UC Riverside, Oak Ridge National Laboratories' Center for Bioenergy Innovation, and the National Renewable Energy Laboratory, supported by funding from the U.S. Department of Energy’s Office of Science.

The study explores the optimal biomass feedstocks and the utilization of extracted lignin. While first-generation biofuels utilize food crops like corn and soy, diverting land and water from food production, the second-generation utilizes non-edible plant biomass, such as wood residues and sugarcane bagasse, offering a more sustainable approach.

Highlighting the potential of CELF biorefineries, the researchers demonstrate that denser feedstocks like hardwood poplar yield greater economic and environmental benefits compared to less carbon-dense alternatives like corn stover. Using poplar in a CELF biorefinery, sustainable aviation fuel could be produced at a break-even price as low as $3.15 per gallon of gasoline-equivalent, significantly undercutting current jet fuel prices in the U.S.

Moreover, the study showcases how lignin utilization can enhance biorefinery economics while minimizing the carbon footprint. Unlike older biorefinery models that predominantly burn lignin for energy, the CELF approach proposes producing renewable chemicals, contributing to carbon sequestration and mitigating climate change.

Encouraged by these findings, the Department of Energy’s Bioenergy Technology Office has granted the researchers a $2 million award to establish a small-scale CELF pilot plant at UC Riverside. Cai envisions that this pilot plant will catalyze further investment in the technology, offering a viable alternative to fossil fuels and combating carbon emissions.

“I began this work more than a decade ago because I wanted to make an impact. I wanted to find a viable alternative to fossil fuels and my colleagues and I have done that,” reflects Cai. “Using CELF, we have shown it is possible to create cost-effective fuels from biomass and lignin and help curb our contribution of carbon emissions into the atmosphere.”

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