Diesel, Made Simply From Coffee Grounds (Ah, the Exhaust Aroma)

In research that touches on two of Americans’ great obsessions — coffee and cars — scientists at the University of Nevada, Reno, have made diesel fuel from used coffee grounds.

The technique is not difficult, they report in The Journal of Agricultural and Food Chemistry, and there is so much coffee around that several hundred million gallons of biodiesel could potentially be made annually.

Mano Misra, a professor of engineering who conducted the research with Narasimharao Kondamudi and Susanta K. Mohapatra, said it was by accident that he realized coffee beans contained a significant amount of oil. “I made a coffee one night but forgot to drink it,” he said. “The next morning I saw a layer of oil floating on it.” He and his team thought there might be a useful amount of oil in used grounds, so they went to several Starbucks stores and picked up about 50 pounds of them.

Analysis showed that even the grounds contained about 10 to 15 percent oil by weight. The researchers then used standard chemistry techniques to extract the oil and convert it to biodiesel. The processes are not particularly energy intensive, Dr. Misra said, and the researchers estimated that biodiesel could be produced for about a dollar a gallon.

One hurdle, Dr. Misra said, is in collecting grounds efficiently — there are few centralized sources of coffee grounds. But the researchers plan to set up a small pilot operation next year using waste from a local bulk roaster.

Even if all the coffee grounds in the world were used to make fuel, the amount produced would be less than 1 percent of the diesel used in the United States annually. “It won’t solve the world’s energy problem,” Dr. Misra said of his work. “But our objective is to take waste material and convert it to fuel.” And biodiesel made from grounds has one other advantage, he said: the exhaust smells like coffee.