The Air Force is testing a jet fuel made from coal and plant biomass that could replace petroleum-based fuel and emit less carbon-dioxide compared to using conventional jet fuels. The fuel is made with a process developed by Accelergy, based in Houston, using technology licensed from ExxonMobil Research and Engineering Company and the Energy and Environmental Research Center at the University of North Dakota.
Other recently tested experimental biofuels for jets have required that the aircraft still use at least 50 percent petroleum-based product to meet performance requirements, particularly for the most advanced military jets. But the Accelergy process produces fuels that closely resemble petroleum-based fuels, making it possible to do away with petroleum altogether. Because of this, the new process could help the Air Force meet its goal of using domestic, lower-carbon fuels for half of its fuel needs by 2016. Although the first products will be jet fuels, the process can also be adapted to produce gasoline and diesel.
The fuel has passed through an initial round of testing, including lab-scale engine tests, and is on track to be flight-tested in 18 months, says Rocco Fiato, vice president of business development at Accelergy.
Turning coal into liquid fuels is nothing new, but such processes have been inefficient and produced large amounts of CO2 emissions. Accelergy’s approach is different because it uses “direct liquefaction,” which is similar to the process used to refine petroleum. It involves treating the coal with hydrogen in the presence of a catalyst. Conventional technology for converting coal to liquid fuels breaks the coal down into synthesis gas, which is mostly carbon monoxide with a little bit of hydrogen; the hydrogen and carbon are then recombined to produce liquid hydrocarbons, a process that releases carbon dioxide. Because the Accelergy process skips the need to gasify all of the coal–which consumes a lot of energy–before recombining the hydrogen and carbon, it’s more efficient and produces less carbon dioxide. “We don’t destroy the molecule in coal. Instead we massage it, inject hydrogen into it, and rearrange it to form the desired hydrocarbons,” says Timothy Vail, Accelergy’s president and CEO.
The hydrogen for Accelergy’s process comes from two sources–coal and biomass. Accelergy gasifies a portion of the coal they use–about 25 percent of it–as well as cellulosic biomass, from sources such as plant stems and seed husks, to produce syngas. The company then treats the syngas with steam. In this reaction, carbon monoxide reacts with water to form hydrogen and carbon dioxide. Using biomass reduces the net carbon-dioxide emissions, since the biomass absorbed CO2 from the atmosphere as the original plants grew.