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Chemists find more efficient coal-to-diesel conversion
Last Updated Thu, 13 Apr 2006 13:59:46 EDT
CBC News

U.S. scientists say they have found a way to boost the efficiency of a 90-year-old method of converting coal into synthetic diesel fuel.

* INDEPTH: Energy

The two-step chemical process, developed by chemists at Rutgers University in New Jersey and the University of North Carolina at Chapel Hill, converts some of the waste product from the original process into usable diesel.

The researchers said their work could reduce U.S. dependence on oil imports for its energy reserves.

However, they added that their research is still in the early stages, and improvements to their methods are needed before they can be put into practice.

The Fischer-Tropsch process for making synthetic fuels from carbon sources such as coal was invented by German chemists in 1920. It is considered too inefficient and too expensive to compete with traditional oil refining.

The process creates molecules of varying weights made of carbon and hydrogen. The resulting hydrocarbons range from methane gas, with just one carbon atom in each molecule, to liquids with 19 or more carbon atoms in each molecule.

The small hydrocarbons, such as methane and propane, are useful as "natural gas." The larger hydrocarbons, containing 10 to 19 carbon atoms, are useful as diesel fuel.

But the Fischer-Tropsch process also creates a lot of molecules in between, containing four to nine carbon atoms, which are considered waste products of the reactions.

The new process, described in Friday's issue of the journal Science, uses two catalysts to convert these medium-weight hydrocarbons into useful products.

The first catalyst removes hydrogen from the molecules, converting them into olefins, highly reactive chemicals with carbon-carbon double bonds.

The second catalyst "scrambles" the carbon bonds through a process called olefin metathesis, causing the molecules to rearrange themselves. The discoverers of this reaction, a group of American and French chemists, received the Nobel Prize for chemistry in 2005.

The first catalyst then replaces the hydrogen atoms, converting the olefins back into usable hydrocarbons.

The researchers say the reactions involved in their new process are selective and create usable molecules from the medium-weight hydrocarbons that used to be considered byproducts.