NREL Scientists Aim To Turn Caribbean Into Jet Fuel and Batteries

It was not even close. In 2022, seaweed levels floating in the Caribbean smashed the record set in 2018 by 20%. You could see the consequences drifting up on shorelines from Puerto Rico to the Florida coast. Briny piles of brown algae invaded white sand beaches. Locals worried the inundation would harm tourism, clog ports, and release noxious fumes if left to rot.

Unfortunately, record algae blooms are not the only visible consequence of warming ocean waters. Some models suggest higher ocean temperatures increase the risk of powerful hurricanes as well.

“Puerto Rico in particular is still dealing with wood waste from Hurricane Maria five years ago,” said National Renewable Energy Laboratory (NREL) researcher Jacob Kruger. “The wood waste in both Puerto Rico and in other areas of the Caribbean—it’s just been piled up with nowhere to go, because many of the landfills are also at capacity.”

Kruger may be unable to eliminate the pair of waste problems himself, but as the NREL principal investigator for a new multi-institutional research team, he does have an idea that could help: Turn seaweed and wood waste into sustainable aviation fuel and graphite, a material used in electric vehicle batteries.

That idea caught the attention of the U.S. Department of Energy Bioenergy Technologies Office. It awarded the team—with researchers from NREL, University of Puerto Rico, North Carolina State University, and Fearless Fund—more than $2 million to interrogate the idea. If successful, the team thinks the project could help empower a region already impacted by climate change and often underrepresented in economic development.

Breaking It Down: How the Team Plans To Process the Mix
The pair may seem unlikely—but combining wood waste with seaweed could actually offer the team chemical advantages. Together, the sargassum and wood chips create a palatable feedstock of simple sugars microbes can digest into molecules needed to make energy-dense biofuels.

To hone the opportunity, the team will adapt an already well-studied set of biological conversion tools—many developed at NREL—to the unique pairing.

“We envision a sort of a dilute acid pretreatment as our baseline to make the sugars more accessible,” Kruger said. “We might have to look at other chemical or mechanical treatments as well, and then plan to use enzymatic hydrolysis to render the sugars fermentable.”

In simple terms, Kruger and his NREL colleagues will use mild acids or heat to treat algae and wood waste shipped from Puerto Rico. Using a cocktail of carefully selected enzymes, they will digest the resulting pulp into a frothy mixture and separate the liquid from the solids that settle at the bottom.

The sugary liquid, a “hydrolysate,” is easily fermented into ethanol. Technologies already exist to upgrade it into sustainable aviation fuel that is chemically identical to conventional jet fuel but could reduce greenhouse gas emissions by 90%.

And the leftover solids? Though they may be difficult to turn into liquid fuel, they may be a perfect material for making batteries for electric vehicles.

Large pelagic sargassum brown alga seaweed deposit on beach.” Second photo is attached. Alt text: “Overview of process to convert woody waste and sargassum into SAF and graphite, including ensilage, pretreatment, enzymatic hydrolysis, and solid/liquid separation, before the liquids go through fermentation and fuel upgrading and the solids go through pre-carbonization, graphitization, and purification.
A New Supply of Graphite, a Critical Battery Material
Graphite, a soft, crystalline carbon often used in pencils, is the main component for battery anodes, composing up to 30% of a lithium-ion battery’s mass. Demand for the critical battery material is projected to increase more than ninefold by 2030, which has industry searching for new domestic sources, according to Bloomberg New Energy Finance.

“Most graphite produced today is mined at less than 95% purity, while graphite for lithium-ion batteries needs to be more than 99.9% pure,” Kruger explained. “Gaining that last 4%–5% purity is disproportionately expensive, but we think our graphitization technology can economically yield graphite at that purity.”

To verify the analysis, NREL will ship the solids from their lab-scale process to researchers at North Carolina State University. There, researchers will “graphitize” the solids with high heat in the presence of an iron catalyst, which causes the carbon in the solids to link together in a crystalline structure.

Preliminary testing shows the resulting biographite has comparable electrical performance to conventional anodes in some measures like reversible capacity. Still, the researchers caution it will need improvement, a core research and development priority of the team.

A Way To Build a Resilient Caribbean Bioeconomy?
The global energy potential of Caribbean seaweed and wood waste is unmistakable. Up to 1.24 million dry tons of sargassum could be harvested annually near populated coastlines. NREL collaborator Fearless Fund has developed a novel process to harvest it at sea both to ensure quality biomass and to protect the coastal environment.

Blended with 75% wood waste, that resource could yield up to 78 million gallons of sustainable aviation fuel every year. A commercialized process could also produce an estimated 61,000 tons of graphite annually—3.4% of global synthetic graphite production.

The potential for the global clean energy transition is clear. But what might such a Caribbean industry mean for local communities whose beaches are inundated with seaweed and homes damaged by hurricanes?

“We are talking about mitigating waste streams on coastal communities, creating new jobs, and helping to meet energy independence goals, particularly in Puerto Rico,” Kruger said.

To quantify any benefits or consequences, the University of Puerto Rico will conduct a siting study for a potential biorefinery on Puerto Rico. Their proposal centers community-level impacts like odor, noise, increased traffic, educational opportunity, and diversity, equity, and inclusion.

By recruiting student researchers from underserved communities, for example, the team aims to provide hands-on learning to local students both in Puerto Rico and on the U.S. mainland. After all, long-term commercial success may hinge as much on the next generation of diverse, well-trained bioenergy leaders as on the technological readiness of the process.

At an even more fundamental level though, the results of the study could be instructive on the potential of applied science to empower communities to respond and even thrive despite the climate challenges ahead.