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August 2010

Breaking through the Barriers to Biofuels

Expert discusses the science and challenges of using pyrolysis to transform biomass into fuels

Diesel Energy
Cheap, renewable diesel from biomass would improve our nation’s energy security; however, economical processes of converting biomass into fuels don't exist, yet. Professor George Huber of the University of Massachusetts is trying to change that.

Cheap, renewable gasoline, diesel, and jet fuels from agricultural leftovers and other biomass sources would improve our nation’s energy and environmental security; however, economical processes of converting biomass into fuels don’t exist, yet. Professor George Huber of the University of Massachusetts discussed the chemical challenges to creating fuels using two pyrolysis-based approaches at Pacific Northwest National Laboratory’s Frontiers in Catalysis Science and Engineering Seminar Series.

Why pyrolysis: Pyrolysis involves rapid heating of lignocellulosic plant matter, the tough fibrous material that forms the cell walls of plants, in the absence of oxygen. The lignocellulose decomposes, creating 300-plus smaller compounds that are released as vapor. By collecting and cooling the vapors, Huber and his team recover these compounds as bio-oil.

"This oil is the cheapest liquid fuel made from biomass," said Huber. Bio-oil costs less than $1 per gallon of gasoline energy equivalence, making it cheaper in cost than gasoline. However, bio-oil has a ways to go. It is acidic, unstable, and agglomerates with time. Huber and his colleagues are working to eliminate these challenges and turn biomass into affordable, renewable fuel.

Using pyrolysis to create fuels: Huber and his collaborators are exploring catalytic chemistry that converts the raw bio-oil into the types of fuels commonly used today including gasoline, diesel, and jet fuel. Their work includes using hydrogen to assist in both the removal of oxygen via cleavage of carbon-oxygen bonds and carbon-carbon bond scission. In addition, the reactions can result in the addition of hydrogen to the resulting fuel compatible molecules.

Speeding it up: Huber's team also added a recyclable zeolite catalyst to the pyrolysis process. The resulting reactions produce aromatic or ring-based molecules that are used as fuels. The key reactions occur quickly in the zeolite pores at high temperatures.

The size and structure of the zeolite pores influence the speed and efficiency of the reactions. If the pores are too big or too small, a solid carbon deposit is created that poisons the catalyst. Huber and his team determined that the zeolite pores need to be 6 to 6.5 angstroms wide—the width of a few atoms. By understanding the chemistry and optimizing the catalysts and reactor design, Huber’s group achieved up to 60% fuel yield with biomass.

“Chemical catalysis and chemical engineering are critical 21st century needs to help make renewable energy a practical reality,” said Huber.

George Huber: A chemical engineering professor at the University of Massachusetts, Huber is a leader in biofuels and catalysis. He is a sought-after scientist, who led the biomass fuels breakout session for DOE’s national assessment of the catalysis research needs in fuels, and organized the National Science Foundation (NSF) sponsored workshop on "Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels." His work was recognized in 2009 on the cover of the NSF's Science Nation (see video). He has been greatly influenced by the catalysis research at Pacific National Northwest Laboratory.

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