Scientists at the US Lawrence-Berkeley Lab have developed a fuel from a bacterium that packs more energy than even the rocket fuels in use today. In fact, the inspiration for the work appears to have come from rocket fuel. Data from simulation show that the fuel has energy density values exceeding 50 megajoules a litre, compared with 32 MJ for petrol and 35 MJ for RP-1, a kerosene-based rocket fuel.
The scientists have named the new fuel ‘POP-FAME’, for polycyclopropanated fatty acid methyl ester.
LB Lab says that, back in the 1960s, the Soviet Union had developed a petroleum-based rocket fuel called Syntin and used it successfully to launch several Soyuz rockets in the 1970s. Despite its powerful performance, Syntin manufacture was halted due to its high costs and the unpleasant process involved — namely, a series of synthetic reactions with toxic by-products and an unstable, explosive intermediate, says a press release from LB.
POP-FAME’s molecular structure closely resembles Syntin’s. At the heart of the fuel’s structure is the ‘three-carbon’ ring — a triangle with a carbon atom at each vertex. (Each carbon atom combines with two other carbon atoms and two other elements, mostly hydrogen.) This structure is called a cyclopropane; they hold potential energy in their bonds. The scientists began by wondering if such three-carbon-ring-based compounds, which are extremely inflammable, could be produced through the bio-route, using bacteria.
Project leader Jay Keasling, a synthetic biology pioneer and CEO of the Department of Energy’s Joint BioEnergy Institute (JBEI), scoured the scientific literature for organic compounds with three-carbon rings and found just two such materials, both made by a bacterium called streptomyces. (This bacterium is used to make many drugs, including the familiar streptomycin.) One of them had been genetically analysed decades ago due to an interest in its antifungal properties. This product, called jawsamycin, has five three-carbon rings. The scientists identified the genes responsible for the enzymes that can make the three-carbon rings and genetically engineered the bacteria to coax it to produce the desired fuel.
POP-FAME is said to have higher energy densities than Syntin, which means even a small quantity of the fuel can pack considerable energy, making it an ideal rocket fuel. The team’s next goal is to figure out how to remove the two oxygen atoms in each molecule, which are dead weight.
Since publishing their proof-of-concept paper, the scientists have begun work to increase the bacteria’s production efficiency even further to generate enough for combustion testing, the LB release says. They are also investigating how the multi-enzyme production pathway could be modified to create polycyclopropanated molecules of different lengths. “We’re working on tuning the chain length to target specific applications,” said Eric Sundstrom, one of the scientists in the team. “Longer chain fuels would be solids, well-suited to certain rocket fuel applications, shorter chains might be better for jet fuel, and in the middle might be a diesel-alternative molecule.”
However, the scientists haven’t yet produced enough fuel for field tests. You’d need 10 kg of fuel for an actual test in a real rocket engine. “We are not yet there,” says Pablo Cruz-Morales, one of the members of the team. But the scientists’ collaborators at another lab (Sandia National Laboratories) have used computer simulations to estimate how the fuel would perform compared with conventional fuels. They found out that POP-FAME carries more energy than petrol or some conventional rocket fuels.
“Energy density is everything when it comes to aviation and rocketry and this is where biology can really shine,” says Corinne Scown, JBEI’s Director of Technoeconomic Analysis.
Eventually, the scientists hope to engineer the process into a workhorse bacteria strain that could produce large quantities of POP molecules from plant waste food sources (like inedible agricultural residue and brush cleared for wildfire prevention), potentially making the ultimate carbon-neutral fuel, the LB press release says.