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Carbon-neutral aviation biofuels haven’t been able to compete with petroleum. Until now.

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Carbon-neutral aviation biofuels haven’t been able to compete with petroleum. Until now.

A simple new refinery method separates the components of complex plant matter for processing into economically viable, carbon-neutral biofuels and chemicals.
February 15, 2024

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Biofuels could take a big bite out of the world’s transportation emissions, especially aviation. But they  remain expensive and are made from the food crops corn and sugarcane, creating a food vs. fuel quandary.

Researchers now report a new fuel refinery concept to produce economical, sustainable biofuels and useful chemicals from woody plant matter such as agricultural and forestry waste. The refinery is based on a relatively simple pre-treatment process that breaks down complex biomass into usable components.

“The key advance of our study is to demonstrate a biomass to biofuels and bioproducts strategy that can simultaneously achieve both economic viability and carbon neutral operation,” says Charles Cai, a chemical and environmental engineering professor at University of California Riverside. “The key products of this plant model include highly impactful sustainable aviation fuels and specialty chemicals.”

The team’s analysis, published in the journal Energy & Environmental Science, shows that a next-generation biorefinery based on this technology could produce sustainable aviation fuels at market-competitive prices as low as $3.15 per gallon of gasoline equivalent.

Cars, trucks, ships, trains, and airplanes generate about a quarter of the world’s greenhouse gas emissions, according to the United Nations. Electrifying these modes of transport is an ongoing effort worldwide. But fossil fuels are expected to still be a part of the transportation equation until mid-century.

 

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Biofuels offer a near-term solution to reduce carbon emissions from transportation. They are made from renewable sources, and could be used in today’s engines and distributed using existing infrastructure. But making biofuels from non-food sources is critical.

To do that at low cost, researchers need to find a way to break down plant biomass into its components without degrading them. Plant cell walls are built of three main components: cellulose, hemicellulose and lignin. Breaking down biomass into these separate components takes a lot of energy and is costly.

Cai and colleagues designed a process they call co-solvent enhanced lignocellulosic fractionation (CELF). The method, which they first reported in 2013, uses a biomass-derived solvent called tetrahydrofuran (THF) which reacts with hemicellulose, cellulose, and lignin at mild temperatures.

Under various reaction conditions, CELF splits plant matter into separate streams containing different quantities of sugars and lignin. Then, special conversion technologies can transform those components into useful materials. The sugars, for instance, give fuel alcohols, and lignin can be turned into useful specialty chemicals. This increases efficiency and yields and produces better quality products.

The UCR team conducted an in-depth economic and environmental analysis of a CELF refinery that maximizes the utilization of biomass and produce commercially relevant biofuels and bioproducts. They consider three main factors that affect refinery performance: the type of biomass feedstock, type of fuel alcohol product, and the fate of the extracted lignin.

The researchers compared two feedstocks: corn stover, the leftover stalks and leaves of corn plants after harvesting, and poplar, a fast-growing hardwood tree. Because a CELF-based refinery utilizes plant matter efficiently, the researchers found that carbon-dense and lignin-rich poplar had more economic and environmental benefits over corn stover.

“The CELF technology was designed to be simple, low-cost, and robust,” Cai says. “In our testing, we have performed a 750-times scale-up of the CELF pretreatment step with less than 5 percent variance in product composition.” With a $2 million award from the Department of Energy, the team now plans to build a small CELF pilot plant at UC Riverside.

Source: Bruno Colling Klein et al. Economics and global warming potential of a commercial-scale delignifying biorefinery based on co-solvent enhanced lignocellulosic fractionation to produce alcohols, sustainable aviation fuels, and co-products from biomass. Energy Environ. Sci. 2024.

Image created with AI. ©Anthropocene Magazine

 

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