New Reactor Paves the Way for Efficiently Producing Fuel from Sunlight

Solar energy has long been touted as the solution to our energy woes, but while it is plentiful and free, it can't be bottled up and transported from sunny locations to the drearier -- but more energy-hungry -- parts of the world. The process developed by Haile -- a professor of materials science and chemical engineering at the California Institute of Technology (Caltech) -- and her colleagues could make that possible.

The researchers designed and built a two-foot-tall prototype reactor that has a quartz window and a cavity that absorbs concentrated sunlight. The concentrator works"like the magnifying glass you used as a kid" to focus the sun's rays, says Haile.

At the heart of the reactor is a cylindrical lining of ceria. Ceria -- a metal oxide that is commonly embedded in the walls of self-cleaning ovens, where it catalyzes reactions that decompose food and other stuck-on gunk -- propels the solar-driven reactions. The reactor takes advantage of ceria's ability to"exhale" oxygen from its crystalline framework at very high temperatures and then"inhale" oxygen back in at lower temperatures.

"What is special about the material is that it doesn't release all of the oxygen. That helps to leave the framework of the material intact as oxygen leaves," Haile explains."When we cool it back down, the material's thermodynamically preferred state is to pull oxygen back into the structure."

Specifically, the inhaled oxygen is stripped off of carbon dioxide (CO₂) and/or water (H₂O) gas molecules that are pumped into the reactor, producing carbon monoxide (CO) and/or hydrogen gas (H₂). H₂can be used to fuel hydrogen fuel cells; CO, combined with H₂, can be used to create synthetic gas, or"syngas," which is the precursor to liquid hydrocarbon fuels. Adding other catalysts to the gas mixture, meanwhile, produces methane. And once the ceria is oxygenated to full capacity, it can be heated back up again, and the cycle can begin anew.

For all of this to work, the temperatures in the reactor have to be very high -- nearly 3,000 degrees Fahrenheit. At Caltech, Haile and her students achieved such temperatures using electrical furnaces. But for a real-world test, she says,"we needed to use photons, so we went to Switzerland." At the Paul Scherrer Institute's High-Flux Solar Simulator, the researchers and their collaborators -- led by Aldo Steinfeld of the institute's Solar Technology Laboratory -- installed the reactor on a large solar simulator capable of delivering the heat of 1,500 suns.

In experiments conducted last spring, Haile and her colleagues achieved the best rates for CO₂dissociation ever achieved,"by orders of magnitude," she says. The efficiency of the reactor was uncommonly high for CO₂splitting, in part, she says,"because we're using the whole solar spectrum, and not just particular wavelengths." And unlike in electrolysis, the rate is not limited by the low solubility of CO₂in water. Furthermore, Haile says, the high operating temperatures of the reactor mean that fast catalysis is possible, without the need for expensive and rare metal catalysts (cerium, in fact, is the most common of the rare earth metals -- about as abundant as copper).

In the short term, Haile and her colleagues plan to tinker with the ceria formulation so that the reaction temperature can be lowered, and to re-engineer the reactor, to improve its efficiency. Currently, the system harnesses less than 1% of the solar energy it receives, with most of the energy lost as heat through the reactor's walls or by re-radiation through the quartz window."When we designed the reactor, we didn't do much to control these losses," says Haile. Thermodynamic modeling by lead author and former Caltech graduate student William Chueh suggests that efficiencies of 15% or higher are possible.

Ultimately, Haile says, the process could be adopted in large-scale energy plants, allowing solar-derived power to be reliably available during the day and night. The CO₂emitted by vehicles could be collected and converted to fuel,"but that is difficult," she says. A more realistic scenario might be to take the CO₂emissions from coal-powered electric plants and convert them to transportation fuels."You'd effectively be using the carbon twice," Haile explains. Alternatively, she says, the reactor could be used in a"zero CO₂emissions" cycle: H₂O and CO₂would be converted to methane, would fuel electricity-producing power plants that generate more CO₂and H₂O, to keep the process going.

The work was funded by the National Science Foundation, the State of Minnesota Initiative for Renewable Energy and the Environment, and the Swiss National Science Foundation.

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Study Estimates Land Available for Biofuel Crops

Published in the journalEnvironmental Science and Technology, the study led by civil and environmental engineering professor Ximing Cai identified land around the globe available to produce grass crops for biofuels, with minimal impact on agriculture or the environment.

Many studies on biofuel crop viability focus on biomass yield, or how productive a crop can be regionally. There has been relatively little research on land availability, one of the key constraints of biofuel development. Of special concern is whether the world could even produce enough biofuel to meet demand without compromising food production.

"The questions we're trying to address are, what kind of land could be used for biofuel crops? If we have land, where is it, and what is the current land cover?" Cai said.

Cai's team assessed land availability from a physical perspective -- focusing on soil properties, soil quality, land slope, and regional climate. The researchers collected data on soil, topography, climate and current land use from some of the best data sources available, including remote sensing maps.

The critical concept of the Illinois study was that only marginal land would be considered for biofuel crops. Marginal land refers to land with low inherent productivity, that has been abandoned or degraded, or is of low quality for agricultural uses. In focusing on marginal land, the researchers rule out current crop land, pasture land, and forests. They also assume that any biofuel crops would be watered by rainfall and not irrigation, so no water would have to be diverted from agricultural land.

Using fuzzy logic modeling, a technique to address uncertainty and ambiguity in analysis, the researchers considered multiple scenarios for land availability. First, they considered only idle land and vegetation land with marginal productivity; for the second scenario, they added degraded or low-quality cropland. For the second scenario, they estimated 702 million hectares of land available for second-generation biofuel crops, such as switchgrass or miscanthus.

The researchers then expanded their sights to marginal grassland. A class of biofuel crops called low-impact high-diversity (LIHD) perennial grasses could produce bioenergy while maintaining grassland. While they have a lower ethanol yield than grasses such as miscanthus or switchgrass, LIHD grasses have minimal environmental impact and are similar to grassland's natural land cover.

Adding LIHD crops grown on marginal grassland to the marginal cropland estimate from earlier scenarios nearly doubled the estimated land area to 1,107 million hectares globally, even after subtracting possible pasture land -- an area that would produce 26 to 56 percent of the world's current liquid fuel consumption.

Next, the team plans to study the possible effect of climate change on land use and availability."Based on the historical data, we now have an estimation for current land use, but climate may change in the near future as a result of the increase in greenhouse gas emissions, which will have effect on the land availability," said graduate student Xiao Zhang, a co-author of the paper. Former postdoctoral fellow Dingbao Wang, now at the University of Central Florida, also co-wrote the paper."We hope this will provide a physical basis for future research," Cai said."For example, agricultural economists could use the dataset to do some research with the impact of institutions, community acceptance and so on, or some impact on the market. We want to provide a start so others can use our research data."

The Energy Biosciences Institute at U. of I. and the National Science Foundation supported the study.

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Biofuel Grasslands Better for Birds Than Ethanol Staple Corn, Researchers Find

Federal mandates and market forces both are expected to promote rising biofuel production, MSU biologist Bruce Robertson says, but the environmental consequences of turning more acreage over to row crops for fuel are a serious concern.

Ethanol in America is chiefly made from corn, but research is focusing on how to cost-effectively process cellulosic sources such as wood, corn stalks and grasses. Perennial grasses promise low cost and energy inputs -- planting, fertilizing, watering -- and the new study quantifies substantial environmental benefits.

"Native perennial grasses might provide an opportunity to produce biomass in ways that are compatible with the conservation of biodiversity and important ecosystem services such as pest control," Robertson said."This work demonstrates that next-generation biofuel crops have potential to provide a new source of habitat for a threatened group of birds."

With its rich variety of ecosystems, including historic prairie, southern Michigan provided a convenient place to compare bird populations in 20 sites of varying size for each of the three fuel feedstocks. Grassland birds are of special concern, Robertson said, having suffered more dramatic population losses than any other group of North American birds.

In the first such empirical comparison and the first to simultaneously study grassland bird communities across habitat scales, Robertson and colleagues found that bugs and the birds that feed on them thrive more in mixed prairie grasses than in corn. Almost twice as many species made their homes in grasses, while plots of switchgrass, a federally designated model fuel crop, fell between the two in their ability to sustain biodiversity.

The larger the plot of any type, researchers found, the greater the concentration of birds supported. But if grasslands offer conservation and biofuel opportunities, Robertson said, the biodiversity benefits could decrease as biofuel grass feedstocks are bred and cultivated for commercial uniformity.

Robertson was a research associate at MSU's W.K. Kellogg Biological Station in Kalamazoo County during the two-year research project. Today he is an MSU adjunct entomology professor and a postdoctoral fellow at the Smithsonian Conservation Biology Institute Migratory Bird Center in Washington, D.C. His research colleagues included John A. Hannah Distinguished Professor of plant biology Douglas Schemske and research associate Liz Loomis, both at the Kellogg Biological Station; Patrick Doran of The Nature Conservancy in Lansing; and statistician J. Roy Robertson of Battle Creek.

The research was funded by the U.S. Department of Energy Great Lakes Bioenergy Research Center with support from The Nature Conservancy's Great Lakes Fund for Partnership in Conservation Science and Economics. Results were recently published in the scientific journalGCB (Global Change Biology) Bioenergy.

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US Does Not Have Infrastructure to Consume More Ethanol, Study Finds

Wally Tyner, the James and Lois Ackerman Professor of Agricultural Economics, and co-authors Frank Dooley, a Purdue professor of agricultural economics, and Daniela Viteri, a former Purdue graduate student, used U.S. Department of Energy and Environmental Protection Agency data to determine that the United States is at the"blending wall," the saturation point for ethanol use. Without new technology or a significant increase in infrastructure, Tyner predicts that the country will not be able to consume more ethanol than is being currently produced.

The federal Renewable Fuel Standard requires an increase of renewable fuel production to 36 billion gallons per year by 2022. About 13 billion gallons of renewable fuel was required for 2010, the same amount Tyner predicts is the threshold for U.S. infrastructure and consumption ability.

"You can't get there with ethanol," said Tyner, whose findings were published in the December issue of theAmerican Journal of Agricultural Economics.

Tyner said there simply aren't enough flex-fuel vehicles, which use an 85 percent ethanol blend, or E85 stations to distribute more biofuels. According to EPA estimates, flex-fuel vehicles make up 7.3 million of the 240 million vehicles on the nation's roads. Of those, about 3 million of flex-fuel vehicle owners aren't even aware they can use E85 fuel.

There are only about 2,000 E85 fuel pumps in the United States, and it took more than 20 years to install them.

"Even if you could produce a whole bunch of E85, there is no way to distribute it," Tyner said."We would need to install about 2,000 pumps per year through 2022 to do it. You're not going to go from 100 per year to 2,000 per year overnight. It's just not going to happen."

And even if the fuel could be distributed, E85 would have to be substantially cheaper than gasoline to entice consumers to use it because E85 gets lower mileage, Tyner said. If gasoline were$3 per gallon, E85 would have to be$2.34 per gallon to break even on mileage.

There is talk of increasing the maximum amount of ethanol that can be blended with gasoline for regular vehicles from 10 percent to 15 percent. But Tyner said that even if the EPA does allow it, the blending wall would be reached again in about four years.

Tyner said advances in the production of thermo-chemical biofuels, which are created by using heat to chemically alter biomass and create fuels, would be necessary to meet the Renewable Fuel Standard. He said those fuels would be similar enough to gasoline to allow unlimited blending and would increase the amount of biofuel that could be used.

"Producing the hydrocarbons directly doesn't have the infrastructure problems of ethanol, and there is no blend wall because you're producing gasoline," Tyner said."If that comes on and works, then we get there. There is significant potential to produce drop-in hydrocarbons from cellulosic feedstocks."

The U.S. Department of Agriculture funded Tyner's research.

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