New Tandem Catalytic Process Enables More Efficient Fischer-Tropsch Production

14 April 2006

Researchers at Rutgers and the University of North Carolina at Chapel Hill have developed a tandem catalytic system that creates a more efficient Fischer-Tropsch process for the conversion of coal and other carbon feedstocks to synthetic fuels.

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” byproducts from the traditional Fischer-Tropsch process into usable fuels.

Fischer-Tropsch yields a wide distribution of molecular weight hydrocarbon products but without any way to control the desired mix. The low-weight and the high-weight Fischer-Tropsch products are useful—the light as gas and the medium-heavy as diesel fuel.

The problem—the greatest inefficiency of the process—is that you also wind up with a substantial quantity of medium-weight products that are not useful and you are stuck with them.

What we are now able to do with our new catalysts is something no one else has done before. We take all these undesirable medium-weight substances and convert them to the useful higher- and lower-weight products.

With our new catalysts, one can generate productive, clean-burning fuels economically and at unsurpassed levels of efficiency using Fischer-Tropsch.

—Prof. Arnold Goldman, Rutgers

The new process is essence uses one catalyst to set the stage for the use of a second well-known catalytic reaction—olefin metathesis—to produce synthetics more efficiently.

Olefin metathesis, which swaps molecular fragments on either side of a carbon-carbon double bond, has become an efficient and widely-used chemical process in petroleum refining and other industries. Its advantages include the creation of fewer sideproducts and hazardous wastes.

(Yves Chauvin, Robert H. Grubbs and Richard R. Schrock shared the 2005 Nobel Prize in Chemistry for “the development of the metathesis method in organic synthesis.”)

Olefins are unsaturated hydrocarbons—they have double or triple carbon bonds. In a saturated hydrocarbon chain, however, every carbon atom is attached to two hydrogen atoms—i.e.,no double carbon bonds.

There are few effective catalysts for the transformation of saturated hydrocarbons analogous to that achieved by olefin metathesis with unsaturated hydrocarbons.

The Rutgers/UNC team effectively converts the saturated hydrocarbon feedstock to unsaturated hydrocarbons, performs olefin metathesis, and then generates final product.

The first catalyst—a “pincer”-ligated iridium complex) removes hydrogen from the molecules, converting them into olefins (alkane dehydrogenation and olefin hydrogenation). Olefins (also called alkenes) are reactive chemicals with carbon-carbon double bonds.

The second molecular or solid-phase catalyst then combines and rearranges the products through olefin metathesis. The first catalyst then rehydrogenates the rearranged products, creating alkane products.

In one example of the research, the team converted two equivalents of hexane to decane and ethane, as well as a small distribution of other alkanes. Further work is necessary to develop the process commercially.

The work grew out of a National Science Foundation-funded research consortium, the Center for the Activation and Transformation of Strong Bonds, based at the University of Washington.

Resources:

• “Catalytic Alkane Metathesis by Tandem Alkane Dehydrogenation-Olefin Metathesis”; Alan S. Goldman, Amy H. Roy, Zheng Huang, Ritu Ahuja, William Schinski, Maurice Brookhart; Science 14 April 2006: Vol. 312. no. 5771, pp. 257 - 261; DOI: 10.1126/science.1123787

• Chemical and Engineering News: Olefin Metathesis: Big-Deal Reaction

• NSF Center for the Activation and Transformation of Strong Bonds (CATSB)

• Prof. Goldman’s homepage