Converting sugar directly to diesel

Sweet diesel! Scientists have discovered a process to convert sugar directly into renewable diesel that could replace fossil fuels used in vehicles.

University of California, Berkeley scientists found that a long-abandoned fermentation process once used to turn starch into explosives can be used to produce renewable diesel.

Researchers teamed up to produce diesel 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 commercialised within 5-10 years.

While the fuel's cost is still higher than diesel or gasoline made from fossil fuels, 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 feed-stocks  sugar or starch  and making all sorts of renewable things, from fuels to commodity chemicals like plastics, said Dean Toste, professor of chemistry and co-author in a statement.

The late Weizmann's process employs the bacterium Clostridium acetobutylicum to ferment sugars into acetone, butanol and ethanol. Researchers developed a way of extracting the acetone and butanol from the fermentation mixture while leaving most of the ethanol behind, while developing 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 coauthor Harvey 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 feed-stocks 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.