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01/05/2007
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A new process for producing liquid fuels from plant matter (biomass) has been proposed by chemical engineers at Purdue University in the USA, writes Roger Bishop. They say it could meet the fuel needs of the “entire US transportation sector”.
The process involves modifying conventional methods for producing liquid fuels from biomass by adding hydrogen during a step called gasification.
Adding hydrogen suppresses the formation of CO2 and increases the efficiency of the process, making it possible, say the scientists, to produce three times the volume of biofuels from the same quantity of biomass. They are calling the approach a “hybrid hydrogen-carbon process,” or H2CAR.
Rakesh Agrawal, Purdue’s Winthrop E Stone Distinguished Professor of Chemical Engineering, says: “Further research is needed to make this a large-scale reality [but] we could use H2CAR to provide a sustainable fuel supply to meet the needs of the entire US transportation sector.”
The process is detailed in a research paper just released 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.
Conventionally, turning biomass or coal into liquid fuels involves breaking down the raw material with a chemical process that gasifies it into CO2, CO and H2. These are then turned into a liquid fuel.
In the H2CAR concept, hydrogen would be harvested by splitting water molecules, possibly via electrolysis. The hydrogen would be added during the gasification step, making the process more efficient by suppressing the formation of CO2 and converting all of the carbon atoms to fuel.
When conventional methods are used to convert biomass or coal to liquid fuels, 60 to 70% of the carbon atoms in the starting materials are lost in the process as CO2.
“This waste is due to the fact that you are using energy contained in the biomass to drive the entire process,” he says. “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.
“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,” says Agrawal.
Using coal exclusively to produce liquid fuels for the USA’s transportation sector could deplete all coal deposits in the country in about 90 years, whereas H2CAR would stretch coal reserves to 140 years, according to Agrawal.
In the paper the researchers suggest the chemical processing steps needed to make the new approach practical. But making the concept economically competitive with gasoline and diesel fuel would require finding ways to produce cheap hydrogen from carbon-free sources and developing a new type of gasifier needed for the process.
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Author
Roger Bishop
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