New material cuts energy costs of separating gas for plastics and fuels

 A new type of hybrid material developed at the University of California, Berkeley, could help oil and chemical companies save energy and money -- and lower their environmental impacts -- by eliminating an energy-intensive gas-separation process.

Today, to separate hydrocarbon gas mixtures into the pure chemicals needed to make plastics, refineries "crack" crude oil at high temperatures -- 500 to 600 degrees Celsius -- to break complex hydrocarbons into lighter, short-chain molecules. They then chill the gaseous mixture to 100 degrees below zero Celsius to liquefy and divide the gases into those destined for plastics and those used as fuel for home heating and cooking.

"Cryogenic distillation at low temperatures and high pressures is among the most energy-intensive separations carried out at large scale in the chemical industry, and an environmental problem because of its contributions to global climate change," said Jeffrey Long, a professor of chemistry at the UC Berkeley and a faculty researcher at Lawrence Berkeley National Laboratory.

Long and his UC Berkeley colleagues now have created an iron-based material -- a metal-organic framework, or MOF -- that can be used at high temperatures to efficiently separate these gases while eliminating the chilling.

"You need a very pure feedstock of propylene and ethylene for making some of the most important polymers, such as polypropylene, for consumer products, but refineries dump a lot of energy into bringing the high temperature gases down to cryogenic temperatures," Long said. "If you can do the separation at higher temperatures, you can save that energy. This material is really good at doing these particular separations."

"The research conducted by the Long group exemplifies the potential of MOF-based materials relative to olefin/paraffin separations," said chemist Peter Nickias, a Dow Fellow at Dow Chemical Company in Michigan who was not involved in the research. "More specifically, the ability of the reported iron-based MOF to separate a variety of unsaturated hydrocarbons from saturated species not only shows the versatility of the iron-MOF system, but also clearly reveals the potential of MOFs as alternative adsorbents."

In the chemical industry, ethylene and propylene are called olefins, while methane, ethane and propane are called paraffins.

Long and his colleagues at UC Berkeley, the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., and the University of Amsterdam in the Netherlands report their findings in the March 30 issue of Science.

MOFs for natural gas purification

The iron-MOF is also good at purifying natural gas, which is a mixture of methane and various types of hydrocarbon impurities that have to be removed before the gas can be used by consumers. These impurities can then be sold for other uses, Long said.

"MOF compounds have a very high surface area, which provides lots of area a gas mixture can interact with, and that surface contains iron atoms that can bind the unsaturated hydrocarbons," Long said. "Acetylene, ethylene and propylene will stick to those iron sites much more strongly than will ethane, propane or methane. That is the basis for the separation."

Nickias noted that increased supplies of natural gas from shale have provided more opportunity to extract and use ethylene and propylene from natural gas, and a variety of materials and approaches are being examined to cut energy use during the refining and purification of olefins.

"Significant energy savings could be achieved if a non-distillation separation could be implemented, or more realistically, the load on a cryogenic distillation unit can be reduced via upstream modifications to the process," Nickias said.

Petroleum refined for the chemical industry is typically a mix of hydrocarbons, primarily two-carbon molecules -- ethane, ethylene and acetylene -- and three-carbon chains -- propane and propylene. Cryogenic distillation separates these compounds -- all of them gases at room temperature -- by liquefying them at low temperatures and high pressure, which causes them to separate by density. Ethylene and propylene go into plastic polymers, while ethane and propane are typically used for fuel.

The researchers found that when pumping a gas mixture through the iron-based MOF (Fe-MOF-74), the propylene and ethylene bind to the iron embedded in the matrix, letting pure propane and ethane through. In their trials, the ethane coming out was 99.0 to 99.5 percent pure. The propane output was close to 100 percent pure, since no propylene could be detected.

After the ethane and propane emerge, the MOF can be heated or depressurized to release ethylene and propylene pure enough for making polymers.

"Once you saturate the material - with ethylene, for example -- you shut off the valve, stop the feed gas, warm up the absorber unit and the ethylene would come out in pure form as a gas," Long said.

MOFs are like packed soda straws

Through a microscope, Fe-MOF-74 looks like a collection of narrow tubes packed together like drinking straws in a box. Each tube is made of organic materials and six long strips of iron, which run lengthwise along the tube. Analysis by Long's colleagues at the NIST Center for Neutron Research showed that different light hydrocarbons have varied levels of attraction to the tubes' iron. By passing a mixed-hydrocarbon gas through a series of filters made of the tubes, the hydrocarbon with the strongest affinity can be removed in the first filter layer, the next strongest in the second layer, and so forth.

"It works well at 45 degrees Celsius, which is closer to the temperature of hydrocarbons at some points in the distillation process," said coauthor Wendy Queen, a postdoctoral fellow at NIST who worked for six months in Long's UC Berkeley lab. "The upshot is that if we can bring the MOF to market as a filtration device, the energy-intensive cooling step potentially can be eliminated. We are now trying out metals other than iron in the MOF in case we can find one that works even better."

Long and his laboratory colleagues are developing iron-based MOFs to capture carbon from smokestack emissions and sequester it to prevent its release into the atmosphere as a greenhouse gas. Similar MOFs, which can be made with different pore sizes and metals, turn out to be ideal for separating different types of hydrocarbons and for storing hydrogen and methane for use as fuel.

Long's other colleagues are UC Berkeley graduate students Eric D. Bloch and Joseph M. Zadrozny; Rajamani Krishna of the Van't Hoff Institute for Molecular Sciences at the University of Amsterdam; and Craig M. Brown of NIST and The Bragg Institute at the Australian Nuclear Science and Technology Organisation in Menai, New South Wales.

The research is part of the Center for Gas Separations Relevant to Clean Energy Technologies, an Energy Frontier Research Center funded by the Department of Energy that focuses primarily on creating novel materials for capturing and storing carbon dioxide.

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The above story is reprinted from materials provided by University of California - Berkeley. The original article was written by Robert Sanders.

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E. coli bacteria engineered to eat switchgrass and make transportation fuels

 A milestone has been reached on the road to developing advanced biofuels that can replace gasoline, diesel and jet fuels with a domestically-produced clean, green, renewable alternative.

Researchers with the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI) have engineered the first strains of Escherichia colibacteria that can digest switchgrass biomass and synthesize its sugars into all three of those transportation fuels. What's more, the microbes are able to do this without any help from enzyme additives.

"This work shows that we can reduce one of the most expensive parts of the biofuel production process, the addition of enzymes to depolymerize cellulose and hemicellulose into fermentable sugars," says Jay Keasling, CEO of JBEI and leader of this research. "This will enable us to reduce fuel production costs by consolidating two steps -- depolymerizing cellulose and hemicellulose into sugars, and fermenting the sugars into fuels -- into a single step or one pot operation."

Keasling, who also holds appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkley, is the corresponding author of a paper in the Proceedings of the National Academy of Sciences (PNAS) that describes this work. The paper is titled "Synthesis of three advanced biofuels from ionic liquid-pretreated switchgrass using engineered Escherichia coli."

Advanced biofuels made from the lignocellulosic biomass of non-food crops and agricultural waste are widely believed to represent the best source of renewable liquid transportation fuels. Unlike ethanol, which in this country is produced from corn starch, these advanced biofuels can replace gasoline on a gallon-for-gallon basis, and they can be used in today's engines and infrastructures. The biggest roadblock to an advanced biofuels highway is bringing the cost of producing these fuels down so that they are economically competitive.

Unlike the simple sugars in corn grain, the cellulose and hemicellulose in plant biomass are difficult to extract in part because they are embedded in a tough woody material called lignin. Once extracted, these complex sugars must first be converted or hydrolyzed into simple sugars and then synthesized into fuels. At JBEI, a DOE Bioenergy Research Center led by Berkeley Lab, one approach has been to pre-treat the biomass with an ionic liquid (molten salt) to dissolve it, then engineer a single microorganism that can both digest the dissolved biomass and produce hydrocarbons that have the properties of petrochemical fuels.

"Our goal has been to put as much chemistry as we can into microbes," Keasling says. "For advanced biofuels this requires a microbe with pathways for hydrocarbon production and the biomass-degrading capacity to secrete enzymes that efficiently hydrolyze cellulose and hemicellulose. We've now been able to engineer strains of Escherichia coli that can utilize both the cellulose and hemicellulose fractions of switchgrass that's been pre-treated with ionic liquids."

E. coli bacteria normally cannot grow on switchgrass, but JBEI researchers engineered strains of the bacteria to express several enzymes that enable them to digest cellulose and hemicellulose and use one or the other for growth. These cellulolytic and hemicellulolytic strains of E. coli, which can be combined as co-cultures on a sample of switchgrass, were further engineered with three metabolic pathways that enabled the E. coli to produce fuel substitute or precursor molecules suitable for gasoline, diesel and jet engines. While this is not the first demonstration of E. coli producing gasoline and diesel from sugars, it is the first demonstration of E. coli producing all three forms of transportation fuels. Furthermore, it was done using switchgrass, which is among the most highly touted of the potential feedstocks for advanced biofuels.

Gregory Bokinsky, a post-doctoral researcher with JBEI's synthetic biology group and lead author of the PNAS paper, explains that the pre-treatment of the switchgrass with ionic liquids was essential to this demonstration.

"The magic is in the ionic liquid pre-treatment," Bokinsky says. "If properly optimized, I suspect you could use ionic liquid pre-treatment on any plant biomass and make it readily digestible by microbes. For us it was the combination of biomass from the ionic liquid pretreatment with the engineered E. coli that enabled our success."

The JBEI researchers also attribute the success of this work to the "unparalleled genetic and metabolic tractability" of E. coli, which over the years has been engineered to produce a wide range of chemical products. However, the researchers believe that the techniques used in this demonstration should also be readily adapted to other microbes. This would open the door to the production of advanced biofuels from lignocellulosic feedstocks that are ecologically and economically appropriate to grow and harvest anywhere in the world. For the JBEI researchers, however, the next step is to increase the yields of the fuels they can synthesize from switchgrass.

"We already have hydrocarbon fuel production pathways that give far better yields than what we obtained with this demonstration," says Bokinsky. "And these other pathways are very likely to be compatible with the biomass-consumption pathways we've engineered into our E. coli. However, we need to find enzymes that can both digest more of the ionic liquid pre-treated biomass and be secreted by E coli. We also need to work on optimizing the ionic liquid pre-treatment steps to yield biomass that is even easier for the microbes to digest."

Co-authoring the PNAS paper with Keasling and Bokinsky were Pamela Peralta-Yahya, Anthe George, Bradley Holmes, Eric Steen, Jeffrey Dietrich, Taek Soon Lee, Danielle Tullman-Ercek, Christopher Voigt and Blake Simmons.

This research was supported in part by the DOE Office of Science and a UC Discovery Grant.

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The above story is reprinted from materials provided by DOE/Lawrence Berkeley National Laboratory.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Gregory Bokinsky, Pamela P. Peralta-Yahya, Anthe George, Bradley M. Holmes, Eric J. Steen, Jeffrey Dietrich, Taek Soon Lee, Danielle Tullman-Ercek, Christopher A. Voigt, Blake A. Simmons, Jay D. Keasling. Synthesis of three advanced biofuels from ionic liquid-pretreated switchgrass using engineered Escherichia coli. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1106958108

Solar rays could replace petroleum fuels, research shows

Alternative fuel sources for cars may have a glowing future as a Kansas State University graduate student is working to replace petroleum fuels with ones made from sunlight.

Yen-Ting Kuo, a doctoral candidate in chemistry, Taiwan, has spent several years in K-State's chemistry program working to create new materials that better use sunlight in chemical reaction processes to generate energy.

"People tend to think of chemistry as test-tube experiments and not really creating practical things. That's just not true," Kuo said. "A big focus now is on 'green chemistry.' This means wanting to have the same quality of life that we have right now, but using chemistry to replace some things with materials that are more eco-friendly, such as biodegradable products or clean fuel."

As a way to advance the clean fuel research, Kuo is making and studying metal-oxide catalysts that react with light. These catalysts, called photocatalysts, cause a chemical reaction when triggered by sunlight, but are not destroyed during the reaction. Photocatalysts are crucial to producing new fuels, like solar gasoline, which use hydrogen.

To make solar gasoline, sunlight is channeled into a tank of water that contains photocatalysts. The sunlight triggers the photocatalysts to react with the water. This reaction causes the water to split into hydrogen and oxygen. When the hydrogen is combined with carbon monoxide it forms a synthetic gas -- called syngas -- that is the basic building block in fossil fuel and can be used to power cars.

In recent years solar gasoline has been getting more mileage as more international laboratories attempt to improve and perfect the process. But developing a photocatalyst that efficiently uses sunlight to create a chemical reaction and produce hydrogen is proving difficult for researchers. It also is needed for production to reach commercial levels. Kuo is working to solve that problem by creating and analyzing new photocatalysts in the lab.

To make a photocatalyst, Kuo mixes various elements in powdered form, and then cooks them at temperatures between 700 degrees Celsius and 850 degrees Celsius.

Once the material is made, its structure is studied with a transmission electron microscope and ultraviolet spectrums. Doing this allows Kuo to look at ways to structurally improve the photocatalyst and its performance.

In addition to improving the material's photocatalytic properties -- which will intensify reaction with the sunlight -- Kuo focuses on increasing the material's surface area. An increased surface area means bigger and better reactions, and a material with a high surface area and with high photocatalytic properties could mean a bright future for solar gasoline and other alternative fuels.

Engineering a photocatalyst that efficiently splits water into hydrogen and oxygen could also be a boon to fuel cell technology, Kuo said. Fuel cells operate by essentially reversing the chemical reaction that's used to split water. Hydrogen is converted into electrical power, and water is given off as a byproduct.

"Even though the mature technology of fuel cells is in the near future, the source of hydrogen is still a question since most of the hydrogen sources now are from petroleum," Kuo said. "Therefore, water splitting using photocatalysts is one of the solutions providing a new pathway to obtain hydrogen."

Kuo came to K-State after reading work published from his adviser, Ken Klabunde. Klabunde, a university distinguished professor of chemistry, is an expert in turning chemistry into new environmentally-friendly materials. He's created inorganic materials and nanotechnology that filter water and air; control odor, bacteria and viruses; and detoxify hazardous chemical spills.

Kuo will defend his dissertation, "Novel photocatalytic water splitting with the N-doped In2O3/TiO2 D10-D0 configuration composite oxide semiconductors," in mid-September. He then will begin a postdoctoral position at the University of Michigan, one of the few universities in the U.S. to study solar gasoline.

Provided by Kansas State University (news : web)

E. coli metabolism reversed for speedy production of fuels, chemicals

In a biotechnological tour de force, Rice University engineering researchers this week unveiled a new method for rapidly converting simple glucose into biofuels and petrochemical substitutes. In a paper published online in Nature, Rice's team described how it reversed one of the most efficient of all metabolic pathways -- the beta oxidation cycle -- to engineer bacteria that produce biofuel at a breakneck pace.

Just how fast are Rice's single-celled chemical factories? On a cell-per-cell basis, the bacteria produced the butanol, a biofuel that can be substituted for gasoline in most engines, about 10 times faster than any previously reported organism.

"That's really not even a fair comparison because the other organisms used an expensive, enriched feedstock, and we used the cheapest thing you can imagine, just glucose and mineral salts," said Ramon Gonzalez, associate professor of chemical and biomolecular engineering at Rice and lead co-author of the Nature study.

Gonzalez's laboratory is in a race with hundreds of labs around the world to find green methods for producing chemicals like butanol that have historically come from petroleum.

"We call these 'drop-in' fuels and chemicals, because their structure and properties are very similar, sometimes identical, to petroleum-based products," he said. "That means they can be 'dropped in,' or substituted, for products that are produced today by the petrochemical industry."

Butanol is a relatively short molecule, with a backbone of just four carbon atoms. Molecules with longer carbon chains have been even more troublesome for biotech producers to make, particularly molecules with chains of 10 or more carbon atoms. Gonzalez said that's partly because researchers have focused on ramping up the natural metabolic processes that cells use to build long-chain fatty acids. Gonzalez and students Clementina Dellomonaco, James Clomburg and Elliot Miller took a completely different approach.

"Rather than going with the process nature uses to build fatty acids, we reversed the process that it uses to break them apart," Gonzalez said. "It's definitely unconventional, but it makes sense because the routes nature has selected to build fatty acids are very inefficient compared with the reversal of the route it uses to break them apart."

The beta oxidation process is one of biology's most fundamental, Gonzalez said. Species ranging from single-celled bacteria to human beings use beta oxidation to break down fatty acids and generate energy.

In the Nature study, Gonzalez's team reversed the beta oxidation cycle by selectively manipulating about a dozen genes in the bacteria Escherichia coli. They also showed that selective manipulations of particular genes could be used to produce fatty acids of particular lengths, including long-chain molecules like stearic acid and palmitic acid, which have chains of more than a dozen carbon atoms.

"This is not a one-trick pony," Gonzalez said. "We can make many kinds of specialized molecules for many different markets. We can also do this in any organism. Some producers prefer to use industrial organisms other than E. coli, like algae or yeast. That's another advantage of using reverse-beta oxidation, because the pathway is present in almost every organism."

Provided by Rice University (news : web)

Iowa State hybrid lab combines technologies to make biorenewable fuels and products

Laura Jarboe pointed to a collection of test tubes in her Iowa State University laboratory.

Some of the tubes looked like they were holding very weak coffee. That meant microorganisms – in this case, Shewanella bacteria – were growing and biochemically converting sugars into hydrocarbons, said Jarboe, an Iowa State assistant professor of chemical and biological engineering.

Some of the sugars in those test tubes were produced by the fast pyrolysis of biomass. That's a thermochemical process that quickly heats biomass (such as corn stalks and leaves) in the absence of oxygen to produce a liquid product known as bio-oil and a solid product called biochar. The bio-oil can be used to manufacture fuels and chemicals; the biochar can be used to enrich soil and remove greenhouse gases from the atmosphere.

Iowa State's Hybrid Processing Laboratory on the first floor of the new, state-built Biorenewables Research Laboratory is all about encouraging that unique mix of biochemical and thermochemical technologies. The goal is for biologists and engineers to use the lab's incubators, reactors, gas chromatography instruments and anaerobic chambers to find new and better ways to produce biorenewable fuels and chemicals.

"Biological processes occur well below the boiling point of water, while thermal processes are usually performed hundreds of degrees higher, which makes it hard to imagine how these processes can be combined," said Robert C. Brown, an Anson Marston Distinguished Professor in Engineering, the Gary and Donna Hoover Chair in Mechanical Engineering, and the Iowa Farm Bureau Director of Iowa State's Bioeconomy Institute.

"In fact, these differences in operating regimes represent one of the major advantages of hybrid processing," Brown said. "High temperatures readily break down biomass to substrates that can be fermented to desirable products."

Jarboe's research is one example. She's trying to develop bacteria that can grow and thrive in the chemicals and compounds that make up bio-oil. That way, they can ferment the sugars from bio-oil with greater efficiency and produce more biorenewable fuels or chemicals.

Another example of mixing the biochemical with the thermochemical is the work of Zhiyou Wen, an associate professor of food science and human nutrition, and Yanwen Shen, a doctoral student in his research group.

They're working to break down a bottleneck in the fermentation of synthesis gas – a mixture of carbon monoxide and hydrogen that's produced by the partial combustion of biomass in a gasifier. The fermentation process slows when researchers dissolve the gas into a liquid that can be used by microorganisms to produce biofuels. They're looking for bioreactor technologies that boost the mass transfer of the synthesis gas without adding energy costs.

A third example is the work of DongWon Choi, a former doctoral student and post-doctoral research associate at Iowa State who's now an assistant professor of biological and environmental sciences at Texas A&M University Commerce. He continues to collaborate in the hybrid lab by working with microalgae that convert carbon dioxide into oil that can be used to produce biofuels.

That oil is currently harvested with solvents or mechanical presses. Both processes produce a lot of waste and the resulting waste management problems. Choi is using pyrolysis technology to heat the algae and convert it into jet and diesel fuels without the waste.

And the researchers say the hybrid lab's mix of people, technologies, equipment and ideas is beginning to show results.

"The hybrid lab provides enormous opportunities for performing biological-based processes for producing biofuel from thermochemically treated biomass," Wen said.

Yes, said Jarboe, "I think it is working well. This is a long process, but we're writing research proposals and papers. Everybody loves the idea of this hybrid approach. It has such a promising future; the challenge is in the collaboration."

The hybrid lab is starting to make the collaboration easier, though.

Brown said he's noticed the students who work in the hybrid lab seem to be comfortable crossing thermochemical and biochemical lines: "Just like children from different cultures often learn to communicate with one another more quickly than do their parents, graduate students seem to pick up cross disciplinary culture and language faster than their faculty advisers."

Provided by Iowa State University (news : web)

Nanoparticles help scientists harvest light with solar fuels

 The humble alga, hated by boaters and pool owners, may someday help provide us with the raw machinery to power our appliances.

Utschig and Tiede are part of Argonne's Photosynthesis Group, which has worked for fifty years to understand photosynthesis—one of the most mysterious and wonderful chemical processes in the world. Photosynthesis built a green Earth out of the bare, meteor-blistered planet which had sat empty for a billion years; it tipped the composition of the atmosphere towards oxygen, allowing all kinds of life to blossom, including us.

The chemistry group is part of a larger effort to develop efficient ways to produce what are termed solar fuels. Most people think of solar panels when they think of solar energy, but the energy that solar panels generate has to be used right away—they directly create electricity, which can't be stored easily.

The alternative is solar fuels, which pull energy from the sun to create fuel that can be stored for later, such as hydrogen. Hydrogen, a promising fuel in the effort to reduce carbon dioxide emissions, is appealingly clean: when it's burned as fuel, water is the byproduct. But we have yet to discover a low-cost way to manufacture large amounts of hydrogen.

"Basically, we've been reverse-engineering photosynthesis," said Argonne chemist David Tiede, who co-authored the paper. "If we understand how Nature does it, we can tweak the process to produce hydrogen."

Most solar fuel efforts focus on a type of protein complex called Photosystem I, or PSI, which is the first half of the photosynthetic duo found in all green plants.

When light strikes the PSI complex, it momentarily knocks an electron into an "excited" state. The goal is to separate this electron from its home atom—leaving behind a "hole" of positive charge—and channel it to an artificial catalyst to make hydrogen. But the electron only remains excited for the tiniest fraction of a second; the catalyst needs to grab it during this tiny window.

With co-author Nada Dimitrijevic, the team designed platinum nanoparticle catalysts. These catalysts have a size and surface chemistry that allows them to stick to PSI molecules at the point where the light-generated electrons accumulate. When the modified platinum nanoparticles and PSI are mixed in water, the two link together.

"The platinum nanoparticles have the same size and surface charge as the molecule that PSI would bind to naturally," Tiede said.

Because the study design used platinum as a catalyst, which is too expensive to be cost-effective, the research serves as proof-of-concept. Further studies hope to improve the method's efficiency, reliability and economics.

"The next step we'll take is experimenting with non-platinum catalysts," Utschig said. "Hopefully we can find a catalyst that can be made with a cheaper metal, which would make the process much more attractive on a large scale."

The paper, "Photocatalytic Hydrogen Production from Noncovalent Biohybrid Photosystem I/Pt Nanoparticle Complexes," was published in the Journal of Physical Chemistry Letters and is available online.

Provided by Argonne National Laboratory (news : web)

A renewable twist on fossil fuels

 Pulling valuable fuels out of thin air? It sounds like magic, but Joel Rosenthal, a chemist at the University of Delaware, is working to transform carbon dioxide (CO2), a greenhouse gas in the atmosphere, into gas for your car and clean-energy future fuels.

Such a feat could help reduce the rising CO2 levels implicated in global warming and also offer a new method of renewable energy production.

Oak Ridge Associated Universities (ORAU), a consortium of 98 Ph.D.-granting universities, of which UD is a member, has selected Rosenthal to receive the Ralph E. Powe Junior Faculty Enhancement Award to pursue the novel research. Rosenthal is one of 30 award winners nationwide.

The competitive award, which provides $5,000 in seed funding from ORAU and $5,000 in matching funding from the faculty member's university, is intended to enrich the research and educational growth of young faculty and serve as a springboard to new funding opportunities.

Rosenthal and his team are designing electrocatalysts from metals such as nickel and palladium that will freely give away electrons when they react with carbon dioxide, thus chemically reducing this greenhouse gas into energy-rich carbon monoxide or methanol.

Besides its use in making plastics, solvents, carpet and other products, methanol fuels race cars in the United States and currently is being researched as a hydrogen carrier for fuel cell vehicles.

Carbon monoxide is an important precursor to liquid hydrocarbons in the energy arena, in addition to its applications as an industrial chemical for producing plastics to detergents to the acetic acid used in food preservation, drug manufacturing and other fields.

"The catalytic reduction of carbon dioxide to carbon monoxide is an important transformation that would allow for the mitigation of atmospheric CO2 levels, while producing an energy-rich substrate that forms a basis for fuels production," Rosenthal says.

"The chemistry we're doing is energetically uphill -- it's an energy-storing process rather than a downhill, energy-liberating process," he notes. "And our goal is to make liquid fuel renewably from wind and solar sources, not from typical fossil fuel bases."

As early as junior high, Rosenthal said, he realized that basic life processes are linked to molecular energy conversion. Then his undergraduate and graduate research took off on renewables.

He earned his undergraduate degree in organic chemistry from New York University and his doctorate in inorganic chemistry at MIT while studying how metals catalyze various energy conversion processes. His doctoral adviser at MIT was Dan Nocera, a leading scientist in renewable energy research.

The strong reputation of the chemistry and biochemistry department lured Rosenthal, a New York City native, to UD. He joined the UD faculty this past fall and already has a research group of eight focusing on the project -- one postdoctoral researcher, four graduate students and three undergraduates.

"The CO2 problem is very important, and people have to tackle it," Rosenthal says. "It's my hope to be able to map out the molecular design principles for efficient CO2 conversion into fuels. Then you can think about doing this on a commercially relevant scale."

Conservative estimates predict that by 2050, the rate of global energy consumption will roughly double the rate recorded at the end of the 20th century. Most scientists believe that rising carbon dioxide levels are leading to global climate change.

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Future fuels for everyone powered by the sun

New scheme would use only sunlight, air and water to supply energy for cars, laptops, GPS systems.

"At the California Institute of Technology, they're developing a way to turn sunlight and water into fuel for our cars."--President Barack Obama, Jan. 25, 2011

The Sun is Earth's primary energy source and harnessing its abundant light is the Holy Grail of renewable energy

Now, a group of scientists has demonstrated a new way to use sunlight, water (H2O) and carbon dioxide (CO2)--some of the cheapest and most commonplace stuff on Earth--to make unlimited amounts of fuel to power almost anything, anywhere.

The method uses concentrated heat from the sun to convert water and carbon dioxide into hydrogen (H2) or carbon monoxide (CO). Large amounts of these two gases could be combined to make liquid fuel that fits into America's existing energy economy.

"Alternatively, you could use the H2 and CO to make methane (natural gas) for a gas-fired electricity generator," said Sossina Haile, professor of Materials Science and of Chemical Engineering at California Institute of Technology in Pasadena. "Or, because the fuels we produce are so pure, they could be easily used to run fuel cells, which generate power very efficiently."

The researchers say one of the most exciting things about the discovery is its versatility. "We are not dictating to the user what the energy infrastructure should be," Haile said. "We are making solar energy easy to use by putting it into a form that our industry is used to seeing and making it available on demand."

Doing the two-step

Scientists have long known how to convert water and carbon dioxide into hydrogen and carbon monoxide. But to do it cheaply and efficiently enough to make the process affordable on a wide scale has been the issue. Part of the problem was the need for expensive and rare elements, such as platinum or iridium, to act as catalysts that encourage the conversion to happen.

So Haile and her team took a novel approach; they tried ceria, a material used in the walls of self-cleaning ovens. Ceria is the oxidized or "rust" form of the element cerium, which is more abundant, and therefore cheaper, than other metals that could do the same job.

The new method requires two steps, the first at high temperature using concentrated heat from the sun (about 3,000 degrees Fahrenheit), and the second at a much lower temperature.

Haile describes the process this way, "If we heat ceria up, the material 'naturally' releases some oxygen from its structure. If we then cool it back down, those oxygen vacancies want to be refilled. In other words, the ceria 'exhales' oxygen at high temperature and then 'inhales' it back when the temperature is lowered."

To make fuel, the second step requires the presence of water and carbon dioxide gases. "At lower temperatures, the cerium, the hydrogen and the carbon all want the oxygen, but the cerium wants it most," Haile said. "So the oxygen vacancies in the ceria are filled by stripping oxygen from H2O and CO2, leaving H2 and CO."

An international collaboration

Haile and her Caltech team, supported by an award from the National Science Foundation, recently published a paper describing the breakthrough in the journal Science. For this project, they collaborated with researchers led by Aldo Steinfeld, a renewable energy technology professor at the Swiss Federal Institute of Technology, also called ETH Zürich, in Switzerland. Steinfeld also leads the Solar Technology Laboratory at the Paul Scherrer Institute in Switzerland.

 

Two pieces of equipment were needed for the experiment. The first piece, built at Caltech, is a reactor "just a bit smaller than a gallon-jug," Haile said. The reactor is basically a cylindrical container lined with ceria that has input and output lines for the gases.

The second piece is a solar concentrator, which is the most difficult part to build. The concentrator is basically a set of giant curved mirrors that gather sunlight from a wide area. For this experiment, the researchers were able to use an existing solar concentrator located at the Paul Scherrer Institute.

The Caltech scientists took their reactor to Switzerland and attached it to the bottom of the concentrator, allowing the sunlight to heat up the ceria inside. Then they piped steam and carbon dioxide into the reactor and measured the hydrogen and carbon monoxide gases flowing out.

Cheaper and more efficient

How far reaching could this new technology be and how much oil, gas or coal could it replace?

"The abundance of cerium means that this approach could have a significant impact on our national energy budget," Haile said. Because cerium is 100,000 times more abundant than the precious metal platinum, she said, the cost would be many orders of magnitude smaller.

For this experiment, the efficiency of the reactor at converting sunlight to usable energy measured just under one percent, which Haile said is comparable to other methods. However, this was a first cut, aimed at simply proving that the process is practical and could be done economically.

Before bringing the technology to market, Haile said, the reactor design needs to be much tighter to get better efficiency.

"As a second step, it will be important to develop materials with even better characteristics than ceria," she added.

"Ideally, one wants a material with a smaller temperature swing required as this will also increase efficiency," Haile said. "In addition, if both the high and low temperatures can be lowered, the overall system lifetime will be improved. Better materials could result in a better process."

Provided by National Science Foundation (news : web)