Long-abandoned bacterial fermentation process converts sugar directly to diesel

Nov 07, 2012
UC Berkeley graduate student Zachary Baer works with a fermentation chamber to separate acetone and butanol (top clear layer) from the Clostridium brew at the bottom. The chemicals can be extracted and catalytically altered to make a fuel that burns like diesel. Credit: Robert Sanders

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, University of California, Berkeley, scientists have discovered.

Campus chemists and chemical engineers teamed up to produce fuel from the products of a bacterial fermentation discovered nearly 100 years ago by the first president of Israel, chemist Chaim Weizmann. The retooled process produces a mix of products that contain more energy per gallon than ethanol that is used today 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 , the scientists said the process would drastically reduce 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, UC Berkeley professor of chemistry and co-author of a report on the new development that will appear in the Nov. 8 issue of the journal Nature.

The work by Toste, coauthors Harvey Blanch and Douglas Clark, UC Berkeley professors of chemical and biomolecular engineering, and their colleagues was supported by the Energy Biosciences Institute, a collaboration between UC Berkeley, Lawrence Berkeley National Laboratory and the University of Illinois at Urbana Champaign, and funded by the energy firm BP.

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.

Tests showed that it burned about as well as normal petroleum-based diesel fuel.

"It looks very compatible with diesel, and can be blended like diesel to suit summer or winter driving conditions in different states," said Blanch.

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," Toste said.

The , dubbed ABE for the three chemicals produced, was discovered by Weizmann around the start of World War I in 1914, and allowed Britain to produce acetone, which was needed to manufacture cordite, used at that time as a military propellant to replace gunpowder. The increased availability and decreased cost of petroleum soon made the process economically uncompetitive, though it was used again as a starting material for synthetic rubber during World War II. The last U.S. factory using the process to produce acetone and butanol closed in 1965.

Nevertheless, Blanch said, 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.

The fermentation process used in World War I to make cordite for bullets and artillery shells might find new use today in the production of advanced biofuels. Credit: Wikepedia; it is in the public domain.

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. Tributyrin is not toxic to the bacterium and, like oil and water, doesn't mix with the broth.

Brought together by the EBI, Blanch and Clark found that Toste had discovered a catalytic process that preferred exactly that proportion of acetone, butanol and ethanol to produce a range of hydrocarbons, primarily ketones, which burn similarly to the alkanes found in diesel.

"The extractive fermentation process uses less than 10 percent of the energy of a conventional distillation to get the butanol and acetone out – that is the big energy savings," said Blanch. "And the products go straight into the chemistry in the right ratios, it turns out."

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, Toste said. The catalysts work by binding ethanol and and converting them to aldehydes, which react with acetone to add more carbon atoms, producing longer hydrocarbons.

"To make this work, we had to have the biochemical engineers working hand in hand with the chemists, which means that to develop the process, we had learn each other's language," Clark said. "You don't find that in very many places."

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.

"Diesel could put Clostridium back in business, helping us to reduce global warming," Clark said. "That is one of the main drivers behind this research."

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User comments : 8

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Husky
2 / 5 (1) Nov 07, 2012
good effort, but call me when its cheaper than fossile diesel.

I have higher hopes for the fermentation of chickenmanure by biogas cogeneration plants with ammonia scrubbers.
This produces 400 m3 biogas 1 and a bunch of soil fertillizer from 1 ton manure right next to the poultry house, so it can immediately heat and light the poultry house (low transport losses) and has warm water and electrity to spare for the grid. BTW there is also a way of using black soldier flie larvae to digest chickenmanure and squeeze 278 grams bio oil out of 1000 gr flies and the remainder proteins can be fed back to the chickens, but the biogas fermentation is more efficient and has economics of scale.
Husky
2 / 5 (3) Nov 07, 2012
As for the americans, they got a huge problem with asian carp infesting their rivers, a problem they sooner or later will solve by turning asian carp into biodiesel.
Parsec
not rated yet Nov 07, 2012
good effort, but call me when its cheaper than fossile diesel.

I have higher hopes for the fermentation of chickenmanure by biogas cogeneration plants with ammonia scrubbers.
This produces 400 m3 biogas 1 and a bunch of soil fertillizer from 1 ton manure right next to the poultry house, so it can immediately heat and light the poultry house (low transport losses) and has warm water and electrity to spare for the grid. BTW there is also a way of using black soldier flie larvae to digest chickenmanure and squeeze 278 grams bio oil out of 1000 gr flies and the remainder proteins can be fed back to the chickens, but the biogas fermentation is more efficient and has economics of scale.

No enough chicken poop in the world to power more than a few cars. There is a LOT more cellulose. Having said that, sunlight to power conversion is under 1% at best.
Shakescene21
not rated yet Nov 08, 2012
Fascinating. Every week or so there is another step forward in alternate fuel. The extraction process uses only 10% of the energy that would have been required by distillation, and it can use cheap materials as catalysts. Hopefully this fermentation process can be coupled with an enzyme digestion process that produces sugars from waste cellulose such as cornstalks. Cornstalks in, Biodiesel out.
Anonym
1 / 5 (7) Nov 08, 2012
This term should be in quotes: "fossil fuels." (Laughable, the persistence of this myth in scientific circles.)



JustAnyone
not rated yet Nov 08, 2012
As for the americans, they got a huge problem with asian carp infesting their rivers, a problem they sooner or later will solve by turning asian carp into biodiesel.


Yah. Asian Carp. The one benefit they're providing is they're staying in the food chain long enough to accumulate Mercury pollution and carry it in their dead bodies to the bottom of the lakes. So, eventually, we'll have clean water again and can eat the fish we catch. ... Except the GOP won't allow the EPA to require Mercury scrubbers on coal power plants, so they keep on emitting poisons and I can't eat wild-caught fish!
jimbo92107
1 / 5 (1) Nov 10, 2012
As for the americans, they got a huge problem with asian carp infesting their rivers, a problem they sooner or later will solve by turning asian carp into biodiesel.


You mean "silvertail?" Delicious fish, and it jumps right into your pan!
Anda
5 / 5 (1) Nov 12, 2012
@Anonym, you know you're an idiot, that's why you use that name.
Go read your holy book and leave us alone.

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