Green diesel: Process makes liquid fuel from plants

George Huber

Chemical and Biological Engineering graduate student George Huber (View larger image.)

A NEW, HIGHLY EFFICIENT PROCESS doubles the energy captured from plants such as corn, compared with ethanol production. Graduate students George Huber, Juben Chheda and Chris Barrett and Steenbock Professor James Dumesic invented a four-phase catalytic reactor in which corn and other biomass-derived carbohydrates can be converted to sulfur-free liquid alkanes, resulting in an ideal additive for diesel transportation fuel.

About 67 percent of the energy required to make ethanol is consumed in fermenting and distilling corn. As a result, ethanol production creates 1.1 units of energy for every unit of energy consumed. In the UW-Madison process, the desired alkanes spontaneously separate from water. No additional heating or distillation is required. The result is the creation of 2.2 units of energy for every unit of energy consumed in energy production.

James Dumesic in a laboratory

Steenbock Professor of Chemical and Biological Engineering James Dumesic (View larger image.)

“The fuel we're making stores a considerable amount of hydrogen,” says Dumesic. “Each molecule of hydrogen is used to convert each carbon atom in the carbohydrate reactant to an alkane. It's a very high yield. We don't lose a lot of carbon. The carbon acts as an effective energy carrier for transportation vehicles. It's not unlike the way our own bodies use carbohydrates to store energy.”

About 75 percent of the dry weight of herbaceous and woody biomass is composed of carbohydrates. Because the UW-Madison process works with a range of carbohydrates, a wide range of plants — and more parts of the plant — can be consumed to make fuel.

New lithographic technique provides path to complex nanoelectronics

ABOUT TWO YEARS AGO, a team led by University of Wisconsin-Madison Chemical and Biological Engineering Professor Paul Nealey demonstrated a lithographic technique for creating patterns in the chemistry of polymeric materials used as templates for nanomanufacturing. They deposited a film of block copolymers on a chemically patterned surface such that the molecules arranged themselves to replicate the underlying pattern without imperfections.

That technique works well for creating templates that are neatly ordered in periodic arrays, explains Nealey, who directs the NSF-funded Nanoscale Science and Engineering Center on campus. “But one of the challenges of nanofabrication is integrating these self-assembling materials, that naturally form periodic structures, into existing manufacturing strategies,” he says. “Engineers create microelectronics under free-form design principles. Not everything fits neatly into an array. We've developed a new technique that directs the assembly of blends of block copolymers and homopolymers on chemically nanopatterned substrates. The result is the creation of structures with non-regular geometries. We've now potentially harnessed the fine control over structure dimensions, afforded by self-assembling materials, to allow for the production of complex nanoelectronic devices.”

Current manufacturing processes employing chemically amplified lithography techniques achieve dimensions as small as 50 to 70 nanometers, but that technology might not be extendable as feature dimensions shrink below 30 nanometers.

By merging the latest principles of lithography and self-assembly block-copolymer techniques, Nealey's group worked with the Paul Scherrer Institute in Switzerland developed a hybrid approach that maximizes the benefits and minimizes the limitations of each approach to nanomanufacturing.

Improved catalysts for hydrogen chemistry

A NEW CLASS of near surface alloys (NSAs) that bind hydrogen atoms loosely holds great promise for catalysis. A standard rule for weak bonds is that a higher energy cost is paid in breaking up the H2 molecule, but by using density functional theory calculations, graduate student Jeff Greeley and Associate Professor Manos Mavrikakis determined a new class of NSAs that can yield superior catalytic behavior for hydrogen-related reactions.

“We found that selected NSAs offer an exciting exception to this rule by simultaneously allowing weak hydrogen binding and low H2 dissociation barriers. Weak binding of hydrogen, in turn, can make subsequent reaction steps easier, thereby allowing lower temperatures to be used for reactions on these NSAs,” Mavrikakis says.

Near surface alloys that react at lower temperatures with higher selectivity would be a boon to many chemical and pharmaceutical processes. The discovery could be used to design an NSA that binds carbon monoxide weakly. When combined with the properties of improved hydrogen dissociation, the alloy could be useful as a robust fuel-cell anode.

The methodology was developed in order to identify nanostructures for easy hydrogen chemistry but has a broad base of application and could be applied to identify promising catalysts for a variety of other chemical reactions. NSAs can be prepared with state-of-the-art nanosynthesis techniques, allowing for layer-by-layer control of the desired nanostructures.

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