Diesel Fuel From a New Life for an Old Fermentation Process

UC Berkeley scientists have rediscovered a long-abandoned fermentation process once used to turn starch into explosives can be used to produce renewable diesel fuel.  Berkeley chemists and chemical engineers joined skills to produce diesel fuel from the products of the abandoned bacterial fermentation discovered nearly 100 years ago by the first president of Israel, chemist Chaim Weizmann. The retooled process produces a mix of products and could be commercialized within 5-10 years.

The university press release says the scientists think the fuel’s cost is still higher than diesel or gasoline made from fossil fuels.

Dean Toste, professor of chemistry and co-author of the paper on the new development said, “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.”  The paper appears today, the Nov. 8 issue of the journal Nature.

Toste, coauthors Harvey Blanch and Douglas Clark, professors of chemical and biomolecular engineering, and their colleagues were backed financially by the oil giant BP supporting the Energy Biosciences Institute (EBI), a collaboration between UC Berkeley, Lawrence Berkeley National Laboratory and the University of Illinois at Urbana Champaign.

The cause of the backing may be from a linkage between Toste, whose EBI work is in the development of novel catalysts, and Clark and Branch, who are working on cellulose hydrolysis and fermentation, from a suggestion by BP chemical engineer Paul Willems, who is an EBI associate director. That’s a polite disclosure.  Willems points out the collaboration illustrates the potential value that can come from academic-industry partnerships like the EBI.

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 as Toste developed a catalyst that converted the 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.

Here’s the assertion of note:  Blanch said, “It looks very compatible with diesel, and can be blended like diesel to suit summer or winter driving conditions in different states.”

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.

Toste expands the explanation with, “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.”

Weizmann discovered the process called ABE from the three chemical’s names first letters in 1914, about the start of World War I.  The discovery allowed Britain to produce acetone, which was needed to manufacture cordite, a military propellant developed to replace gunpowder.  In time the increased availability and decreased cost of petroleum made the process economically uncompetitive.

ABE came back to be 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.

Its back again as Blanch explains the process by which the Clostridium bacteria convert sugar or starch to these three chemicals is very efficient. The challenge was for Blanche and the laboratory to investigate ways of separating the fermentation products that would use less energy than the common method of distillation.

The team discovered that several organic solvents could extract the acetone and butanol from the fermentation broth while not extracting much ethanol. The best so far is glyceryl tributyrate, or Tributyrin, because it’s not toxic to the bacterium and, like oil and water, doesn’t mix with the broth.

All together at EBI Blanch and Clark found that Toste had discovered a catalytic process that preferred exactly that proportion of acetone, butanol and ethanol in a Tributyrin solvent yield produces a range of hydrocarbons, primarily ketones, which burn similarly to the alkanes found in diesel.

Blanche takes up further explanation, “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. And the products go straight into the chemistry in the right ratios, it turns out.”

Toste’s 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.  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 said, “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. You don’t find that in very many places.”

Clark looks at the potential pointing out 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 storage alternatives can provide.

The Berkeley team has a very high potential process in hand.  There’s a wide range of raw starch and sugar sources, low energy needs, it looks like a continuous process and the refining as disclosed looks quite simple.  This looks like it has market legs.