Scientists produce diesel by bacterial fermentation sugar

Scientists produce diesel by bacterial fermentation of sugar

6:20 AM, 8th November 2012
Scientists produce diesel by bacterial fermentation of sugar
Graduate student Zachary Baer works with a fermentation chamber in the Energy Biosciences Building to separate acetone and butanol from the yellowish Clostridium brew at the bottom. The chemicals can be extracted and catalytically altered to make a fuel that burns like diesel.

BERKELEY, US: A long-abandoned fermentation process once used to turn starch into explosives can be used to produce renewable diesel fuel to replace the fossil fuels now used in transportation, UC Berkeley scientists have discovered. Researchers produce diesel fuel from the products of a bacterial fermentation discovered nearly 100 years ago by chemist Chaim Weizmann, first president of Israel. The retooled process produces a mix of products that contain more energy per gallon than ethanol that is used in transportation fuels and could be commercialized within 5 - 10 years.

While the fuel’s cost is still higher than diesel or gasoline made from fossil fuels, the scientists said the process would drastically reduce greenhouse gas emissions from transportation, one of the major contributors to global climate change.

“What I am really excited about is that this is a fundamentally different way of taking feedstocks, sugar or starch, and making all sorts of renewable things, from fuels to commodity chemicals like plastics,” said Dean Toste, Professor, UC Berkeley.

The late Weizmann’s process employs the bacterium Clostridium acetobutylicum to ferment sugars into acetone, butanol and ethanol. Blanch and Clark developed a way of extracting the acetone and butanol from the fermentation mixture while leaving most of the ethanol behind, while Toste developed a catalyst that converted this ideally-proportioned brew into a mix of long-chain hydrocarbons that resembles the combination of hydrocarbons in diesel fuel.

The process is versatile enough to use a broad range of renewable starting materials, from corn sugar (glucose) and cane sugar (sucrose) to starch, and would work with non-food feedstocks such as grass, trees or field waste in cellulosic processes. “You can tune the size of your hydrocarbons based on the reaction conditions to produce the lighter hydrocarbons typical of gasoline, or the longer-chain hydrocarbons in diesel, or the branched chain hydrocarbons in jet fuel,” said Toste.

According to Blanch, the process by which the Clostridium bacteria convert sugar or starch to these three chemicals is very efficient. This led him and his laboratory to investigate ways of separating the fermentation products that would use less energy than the common method of distillation. They discovered that several organic solvents, in particular glyceryl tributyrate (tributyrin), could extract the acetone and butanol from the fermentation broth while not extracting much ethanol.

The current catalytic process uses palladium and potassium phosphate, but further research is turning up other catalysts that are as effective, but cheaper and longer-lasting, said Toste. The catalysts work by binding ethanol and butanol and converting them to aldehydes, which react with acetone to add more carbon atoms, producing longer hydrocarbons.

Clark noted that diesel produced via this process could initially supply niche markets, such as the military, but that renewable fuel standards in states such as California will eventually make biologically produced diesel financially viable, especially for trucks, trains and other vehicles that need more power than battery alternatives can provide.

© University of California News

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