Scientists at the Lawrence Berkeley National Laboratory have discovered that an old technique for making explosives can be redeployed to produce biofuel.
The process involves an odd little bacterium called Clostridium acetobutylicum, which once upon a time was used to manufacture cordite, an explosive propellant for artillery shells and bullets. Aside from its century-old roots, the new biofuel production method is also noteworthy for the financial backing of oil company BP (yes, that BP). The company funds a major research collaborative that supported the Berkeley team, called the Energy Biosciences Institute.
The Cordite Connection
Cordite was invented in the 1880’s as a smokeless improvement on gunpowder. It was used extensively in World War I and World War II, most famously in the “Little Boy” atomic bomb that destroyed the Japanese city of Hiroshima.
The solvent acetone is essential for the manufacture of cordite, and typically it was obtained from the mineral calcium acetate. When World War I was in swing, Germany held the market on calcium acetate, so for obvious reasons the British government had to look elsewhere.
It didn’t have to look far, as a British chemist (the Russian-born Chaim Weizmann) had already begun exploiting Clostridium acetobutylicum for creating synthetic rubber through fermentation.
When Weizmann turned his attention to producing acetone through fermentation, he almost immediately ran into a roadblock that will be familiar to biofuel fans today: the corn upon which he relied was unavailable due to wartime food rationing.
Of even greater interest is the fact that wartime shortages in England sparked the construction of at least two acetone fermentation facilities in the corn-rich Midwestern U.S., though apparently both were in operation only for a year or so. By the 1950’s, a low-cost petrochemical process had been discovered for acetone production, and the rest is history.
Bacteria + Chemistry = Biofuel
Fast-forward about 100 years and you find the U.S. rapidly transitioning from food-based biofuel production to the use of non-food biofuel sources, including grasses, weeds, agricultural waste, and even fast-growing trees such as poplar and willow. That’s where Clostridium acetobutylicum re-enters the stage.
The basic problem with woody biomass is lignin, the substance that toughens cell walls and creates a barrier between us and the juicy sugars within. Until recently, breaking down lignin required extra steps and extra expense, making commercial-scale production a pipe dream.
Fermentation is a natural process that provides a low-cost way to get around that obstacle. The Berkeley lab team found that Clostridium acetobutylicum fits the bill as a highly efficient way to render woody biomass sugars into acetone as well as butanol and ethanol, aka the “ABE” products.
After that it was a matter of finding an efficient catalyst that could stretch the short ABE carbon chains into longer ones. The team settled on palladium, a silvery-white metal in the platinum group. They found that depending on the amount of time exposed to palladium, ABE products could be transformed into precursors for producing drop-in substitutes for gasoline, diesel, or jet fuel.
Hopefully, No Slip Between Biofuel Cup and Lip
The sticky wicket, of course, is scaling up the process to a commercially viable level, and to that end the team has already begun identifying even more efficient catalysts than palladium. History also appears to be on the Berkeley team’s side. According to corresponding research author F. Dean Toste:
“The ABE fermentation process was established and scaled nearly a century ago… and while the chemistry portion is less proven on scale, it relies on heterogeneous catalysis, a mainstay of industrial chemistry today.”
Image: Courtesy of Berkeley National Laboratory
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