Green Diesel From Plants To Power Cars

By Roland Piquepaille

Making diesel-like liquid from carbohydrates found in plants has been done before by fermenting glucose into ethanol added to gasoline. But this process was inefficient and expensive because the ethanol needed to be separated from water at the end of the fermentation process. Now, a team of chemists at University of Wisconsin-Madison has found a new way to create green diesel from plants which avoids this costly separating phase. Nature adds that this fuel born from carbohydrates could be clean and easy. And this plant-derived fuel can use existing infrastructures for distribution, which is not the case for hydrogen. But don't rush to your gas station today. Even if this new way to produce green diesel is promising, there are still some challenges to overcome before it becomes commercially available. Read more...

Here is a short description of this new process, provided by the University of Wisconsin-Madison.

University of Wisconsin-Madison College of Engineering researchers have discovered a new way to make a diesel-like liquid fuel from carbohydrates commonly found in plants.

Professor James Dumesic and colleagues [have built] a four-phase catalytic reactor in which corn and other biomass-derived carbohydrates can be converted to sulfur-free liquid alkanes resulting in an ideal additive for diesel transportation fuel.

Nature gives additional details.

A magnesium-based catalyst then knits these molecules together to create the longer carbon chains required for diesel fuel. Adding more pressurized hydrogen, and removing any remaining oxygen atoms with a platinum catalyst, delivers the finished fuel.

Below is a diagram showing the four-phase catalytic processing (Credit: University of Wisconsin-Madison College of Engineering).

This other diagram illustrates the conversion of carbohydrates to a diesel fuel additive (Credit: University of Wisconsin-Madison College of Engineering).

Both of these images come from the headlines news for June 2, 2005 at the University of Wisconsin-Madison College of Engineering.

According to the University, this process is very energy-efficient compared with the production of ethanol.

About 67 percent of the energy required to make ethanol is consumed in fermenting and distilling corn. As a result, ethanol production creates 1.1 units of energy for every unit of energy consumed. In the UW-Madison process, the desired alkanes spontaneously separate from water. No additional heating or distillation is required. The result is the creation of 2.2 units of energy for every unit of energy consumed in energy production.

So will we buy soon such fuels at our gas stations? Here are some answers from Nature.

If all goes according to plan, Dumesic estimates one could grow enough plants in the United States to power a significant percentage of the country's vehicles.

The next challenge is to work out how to extract the all-important carbohydrates from plant matter. The chemists used a pure carbohydrate supply in their tests, and Dumesic says that plants may have to undergo extensive processing to remove unwanted chemicals.

The research work has been published by Science under the title "Production of Liquid Alkanes by Aqueous-Phase Processing of Biomass-Derived Carbohydrates" (Vol. 308, Issue 5727, Pages 1446-1450, June 3, 2005). Here is a link to the abstract (Free registration required).

Sources: University of Wisconsin-Madison College of Engineering news release, June 2, 2005; Mark Peplow, Nature, June 2, 2005; and various websites

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• Chemistry
  
• Energy
  
• Engineering
  
• Environment
  
• Transportation