Purdue University chemical engineers have proposed a new environmentally friendly process for producing liquid fuels from plant matter - or biomass - potentially available from agricultural and forest waste, providing all of the fuel needed for "the entire U.S. transportation sector."
The new approach modifies conventional methods for producing liquid fuels from biomass by adding hydrogen from a "carbon-free" energy source, such as solar or nuclear power, during a step called gasification. Adding hydrogen during this step suppresses the formation of carbon dioxide and increases the efficiency of the process, making it possible to produce three times the volume of biofuels from the same quantity of biomass, said Rakesh Agrawal, Purdue's Winthrop E. Stone Distinguished Professor of Chemical Engineering.
The researchers are calling their approach a "hybrid hydrogen-carbon process," or H2CAR. "Further research is needed to make this a large-scale reality," Agrawal said. "We could use H2CAR to provide a sustainable fuel supply to meet the needs of the entire U.S. transportation sector - all cars, trucks, trains and airplanes."
The process, which would make possible the dawning of a "hydrogen-carbon economy," is detailed in a research paper appearing online this week in the Proceedings of the National Academy of Sciences. The paper was written by Agrawal, chemical engineering doctoral student Navneet R. Singh, and chemical engineering professors Fabio H. Ribeiro and W. Nicholas Delgass. A conventional method for turning biomass or coal into liquid fuels involves first breaking down the raw material with a chemical process that "gasifies" it into carbon dioxide, carbon monoxide and hydrogen. Then those constituents are turned into a liquid fuel with other processes.
In the H2CAR concept, hydrogen would be harvested by splitting water molecules, possibly with a well-known method called electrolysis. Then the hydrogen would be added during the gasification step, making the process more efficient by suppressing the formation of carbon dioxide and converting all of the carbon atoms to fuel.
When conventional methods are used to convert biomass or coal to liquid fuels, 60 percent to 70 percent of the carbon atoms in the starting materials are lost in the process as carbon dioxide, a greenhouse gas, whereas no carbon atoms would be lost using H2CAR, Agrawal said. "This waste is due to the fact that you are using energy contained in the biomass to drive the entire process," he said. "I'm saying, treat biomass predominantly as a supplier of carbon atoms, not as an energy source."
Power for the electrolysis would be provided by carbon-free energy sources, such as solar, wind or nuclear power. And, unlike conventional methods of producing liquid fuels from plant matter and coal, H2CAR would not emit carbon dioxide into the atmosphere. "The goal is to accomplish the complete transformation of every carbon atom in the feedstock to liquid fuel by supplementing the conversion process with hydrogen from a carbon-free energy source," Agrawal said.
Other researchers have estimated that the United States has a sustainable supply of about 1.4 billion tons of biomass each year that could be used specifically...
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