Inexpensive, carbon-neutral biofuels are finally possible

When it comes to making fuel from plants, the first step has always been the hardest: breaking down the plant matter. A new study reveals that introducing a simple, renewable chemical in the pre-treatment step can finally make the production of next-generation biofuels both profitable and carbon neutral.

For biofuels to compete with oil, biorefinery operations must be designed to better utilize lignin. Lignin is one of the main components of plant cell walls. It gives plants greater structural integrity and greater resilience to microbial attack. However, these natural properties of lignin also make it difficult to extract and use from plant material, also known as biomass.

“Using lignin is the gateway to producing what you want from biomass in the most economical and environmentally friendly way possible,” said Charles Cai, associate research professor. at UC Riverside. “Designing a process that can better utilize both lignin and sugars present in biomass is one of the most exciting technical challenges in this field.”

To overcome the lignin hurdle, Cai invented CELF, which stands for co-solvent enhanced lignocellulosic fractionation. This is an innovative biomass pretreatment technology.

“CELF uses tetrahydrofuran or THF to supplement water and dilute acid during biomass pretreatment. This improves overall efficiency and adds lignin extraction capabilities,” Cai said. “Better yet, THF itself can be made from biomass sugars.”

A historical article published in Energy and environmental sciences details the extent to which a CELF biorefinery provides economic and environmental benefits compared to petroleum-based fuels and previous biofuel production methods.

The paper is a collaboration between Cai’s research team at UCR, the Center for Bioenergy Innovation run by Oak Ridge National Laboratories, and the National Renewable Energy Laboratory. In this paper, researchers consider two main variables: what type of biomass is most ideal and what to do with the lignin once it has been extracted.

First-generation biofuel operations use food crops like corn, soybeans, and sugarcane as feedstocks or feedstocks. Since these feedstocks divert land and water from food production, their use for biofuels is not ideal.

Second generation operations use non-edible plant biomass as feedstock. An example of biomass feedstock includes wood residues from milling operations, sugarcane bagasse, or corn stalks, all of which are abundant and inexpensive byproducts of forestry and agricultural operations.

According to the Department of Energy, up to one billion tons of biomass per year could be made available for the manufacture of biofuels and bioproducts in the United States alone, which would replace 30% of our consumption of oil while creating new national jobs.

Because a CELF biorefinery can more fully utilize plant material than previous second-generation methods, researchers have found that a heavier, denser feedstock, such as hardwood poplar, is preferable to less cornstalk. carbon-dense to generate greater economic and environmental benefits.

Using poplar in a CELF biorefinery, researchers demonstrate that sustainable aviation fuel could be produced at a breakeven price as low as $3.15 per gallon of gasoline equivalent. The current average cost of a gallon of jet fuel in the United States is $5.96.

The U.S. government provides credits for biofuel production in the form of Renewable Identification Number Credits, a subsidy intended to support domestic biofuel production. The level of these credits issued for second-generation biofuels, the D3 level, generally trades at $1 per gallon or more. At this price per credit, the newspaper shows that we can expect a rate of return on the operation greater than 20%.

“Spending a little more on a higher carbon feedstock like poplar still generates more economic benefit than a cheaper feedstock like corn stalk, because you can get more fuel and chemicals out of it,” Cai said.

The article also illustrates how the use of lignin can contribute positively to the overall biorefinery economics while keeping the carbon footprint as low as possible. In older biorefinery designs, where biomass is cooked in water and acid, lignin is mostly unusable beyond its calorific value.

“Older models would choose to burn lignin to supplement the heat and energy of these biorefineries, because they could mainly only exploit sugars from biomass – an expensive proposition that leaves a lot of value behind,” Cai said .

In addition to better use of lignin, the CELF biorefinery model also proposes to produce renewable chemicals. These chemicals could be used as building blocks for bioplastics and flavoring compounds for food and drinks. These chemicals absorb some of the carbon from plant biomass that would not be released into the atmosphere as CO.₂.

“Adding THF helps reduce the energy cost of pretreatment and isolates the lignin, so you no longer have to burn it. On top of that, we can make renewable chemicals that help us achieve a near-zero global warming potential,” Cai said. said. “I think this moves the needle from Gen 2 to Gen 2+ biofuels.”

In light of the team’s recent successes, the Department of Energy’s Office of Bioenergy Technology awarded the researchers a $2 million grant to build a small-scale CELF pilot plant at UCR. Cai hopes the pilot plant demonstration will lead to larger-scale investments in the technology, as harnessing energy from fossil fuels contributes to global warming and harms the planet.

“I started this work over 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 did just that,” Cai said. “Through CELF, we have shown that it is possible to create cost-effective fuels from biomass and lignin and help reduce our contribution to carbon emissions into the atmosphere.”