Coal gets a Second Wind.
Train cars filled with coal. Photo by Dallas Powell.
by Mark Derewicz
With global oil supplies stretched to the limit, will the world embrace coal liquefaction? Carolina chemist Maurice Brookhart and Rutgers University chemist Alan Goldman think it’s possible.
The original Fischer-Tropsch coal liquefaction system, developed in 1920s Germany, makes hydrocarbon compounds called alkanes out of coal. Some of the alkanes have between ten and nineteen carbon atoms per molecule and can be used as cleaner-burning diesel fuel. Other molecules contain one to three carbon atoms (methane, ethane, propane) and can be used as gas fuel. But molecules with four to nine carbon atoms are by-products with little value. Compared to oil refining, the process had been thought to be inefficient, expensive, and environmentally hazardous. But when oil prices soared past fifty dollars a barrel, the Fischer-Tropsch system was put back on the table. And now, Brookhart and Goldman have created a way—a dual catalyst system—to convert those “leftover” alkanes into diesel fuels, making the process more efficient.
“One catalyst compound removes hydrogen, converting alkanes into new materials—olefins—that contain carbon-carbon double bonds,” Brookhart says. “And that makes the new material more reactive.” The second catalyst rearranges carbon-carbon bonds. Then, he says, the first catalyst returns hydrogen atoms to the rearranged compounds, which creates two new alkanes with different chain lengths. The longer chains are fuel.
The system still has some big production hurdles. For instance, the process slows and then stops working as one of the catalysts decays, probably because of the reaction’s high heat, Brookhart says. The chemists are trying to improve the system, and, if they succeed, the process could also make fuel from reacting short hydrocarbon chains left over from petroleum refining.
The research has drawn a lot of press attention because coal is abundant in the United States and China. Coal producers in states such as Pennsylvania and Minnesota are already investing in coal liquefaction.
The EPA says that coal diesel burns cleaner than regular diesel or gasoline, but carbon dioxide and other greenhouse gases are still by-products of fuel production and use. Other scientists are developing carbon sequestration methods to help with that. 
Brookhart and Goldman receive funding from the National Science Foundation.
