From Biomass to Biofuels: Finding the Best Path

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Will Medlin

Chemical and Biological Engineering

CU-Boulder assistant professor of chemical and biological engineering Will Medlin says the fact that many important industrial chemicals sell for $25 per gallon or more makes chemical products the “low hanging fruit” in catalysis research and development.

But the bigger potential impact, he maintains—if researchers can get costs low enough—is the efficient conversion of biomass to biofuels that can power our transportation systems in a more sustainable way.

Medlin is the CU-Boulder site director for the Colorado Center for Biorefining and Biofuels (C2B2), a multi-institutional center devoted to the conversion of biomass to fuels and other products. He also is a fellow of the Renewable and Sustainable Energy Institute (RASEI), a joint initiative between the university and the National Renewable Energy Laboratory in Golden.

One of the challenges in creating catalysts for biofuels, he says, is that a catalyst must be highly efficient because adding even pennies to the cost of fuel could mean the difference in it gaining wide-scale acceptance. So the chemical process must be fully optimized to be viable from an economic perspective.

Plant-derived biomass also is more highly oxygenated than petroleum-based feedstocks, and thus presents a new challenge to chemical engineers who must determine how to upgrade biomass-derived compounds efficiently and produce liquid fuel with good combustion and thermochemical properties.

Medlin’s research group focuses on the design of heterogeneous catalysts based on a molecular-scale understanding of the oxygenate-catalyst interaction to see if they can enhance the conversion of biomass into chemicals and fuels.

The work is of great interest to the energy industry, including ConocoPhillips, which is funding a faculty fellowship for Medlin, and some two dozen other sponsors of C2B2.

“Solid catalysts are advantageous to work with because they’re more easily recoverable, but the disadvantage is that a lot less is known about how they work,” Medlin says. “Many of the catalysts we are looking at incorporate expensive metals—platinum, rhodium, and palladium—so we need to design catalysts that are as efficient as possible to minimize the cost.”

"Many of the catalysts we are looking at incorporate expensive metals—so we need to design ones that are as efficient as possible to minimize cost."-Will Medlin

One of the most common examples of a heterogeneous catalyst is a catalytic converter that breaks down the harmful byproducts of automobile exhaust. Catalytic converters typically incorporate precious metals, which are coated on structures that are designed to maximize the surface area and contact with the reactant.

In Medlin’s lab, seven undergraduates join 11 PhD students and one post-doc in designing and testing supported metal catalysts. The metals on these catalysts are dispersed onto inert support materials to maximize the surface area of the expensive metals. The support materials are highly porous, such that approximately 10 grams of the material may have as much surface area as a football field.

Medlin’s group focuses primarily on “downstream” chemistry that is largely independent of the type of biomass feedstock, and thus would work for switchgrass, algae, or other kinds of plant material. These downstream technologies involve reactions of deconstructed biomass that has already been decomposed into its components, including sugars and fats. Other C2B2 researchers conduct investigations of upstream technologies used to break down agricultural biomass into small molecules.

Medlin and his students base their catalyst designs on a fundamental understanding of how the catalyst works. To gain this understanding, they employ powerful spectroscopic techniques (such as high-resolution electron energy loss spectroscopy) to observe how reactions occur on surfaces at the molecular scale. By learning how these molecular transformations are related to the structure and composition of the catalyst, they can design catalysts from a rational basis rather than through trial-and-error approaches.

“Our hypothesis is that the way the reactant attaches to the surface of the catalyst determines how it breaks down,” Medlin explains, “so we investigate methods for forming the kinds of attachments that should be optimal for a given reaction. This helps us design cheaper, more efficient catalysts for producing biofuels and biochemicals.”

The work already has led to one patent, and two recent invention disclosures are pending.

Medlin also was awarded the college’s 2009 Charles Hutchison Memorial Teaching Award for instructional innovations, which include mentoring a large number of students in discovery learning in his laboratory and just-in-time classroom teaching approaches that emphasize active learning.

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