Thursday, October 13, 2011

New advanced biofuel identified as an alternative to diesel fuel

 Researchers with the U.S Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI) have identified a potential new advanced biofuel that could replace today's standard fuel for diesel engines but would be clean, green, renewable and produced in the United States.

Using the tools of synthetic biology, a JBEI research team engineered strains of two microbes, a bacteria and a yeast, to produce a precursor to bisabolane, a member of the terpene class of chemical compounds that are found in plants and used in fragrances and flavorings. Preliminary tests by the team showed that bisabolane's properties make it a promising biosynthetic alternative to Number 2 (D2) diesel fuel.

"This is the first report of bisabolane as a biosynthetic alternative to D2 diesel, and the first microbial overproduction of bisabolene in Escherichia coli and Saccharomyces cerevisiae," says Taek Soon Lee, who directs JBEI's metabolic engineering program and is a project scientist with Lawrence Berkeley National Laboratory (Berkeley Lab)'s Physical Biosciences Division. "This work is also a proof-of-principle for advanced biofuels research in that we've shown that we can design a biofuel target, evaluate this fuel target, and produce the fuel with microbes that we've engineered."

Lee is the corresponding author of a paper reporting this research in the journal Nature Communications. Co-authoring this paper were Pamela Peralta-Yahya, Mario Ouellet, Rossana Chan, Aindrila Mukhopadhyay and Jay Keasling.

The rising costs and growing dependence upon foreign sources of petroleum-based fuels, coupled with scientific fears over how the burning of these fuels impacts global climate, are driving the search for carbon-neutral renewable alternatives. Advanced biofuels -- liquid transportation fuels derived from the cellulosic biomass of perennial grasses and other non-food plants, as well as from agricultural waste -- are highly touted for their potential to replace gasoline, diesel and jet fuels. Unlike ethanol, which can only be used in limited amounts in gasoline engines and can't be used at all in diesel or jet engines, plus would corrode existing oil pipelines and tanks, advanced biofuels are drop-in fuels compatible with today's engines, and delivery and storage infrastructures.

"We desperately need drop-in, renewable biofuels that can directly replace petroleum-derived fuels, particularly for vehicles that cannot be electrified," says co-author Keasling, CEO of JBEI and a leading authority on advanced biofuels. "The technology we describe in our Nature Communications paper is a significant advance in that direction."

JBEI is one of three Bioenergy Research Centers established by the DOE's Office of Science in 2007. Researchers at JBEI are pursuing the fundamental science needed to make production of advanced biofuels cost-effective on a national scale. One of the avenues being explored is sesquiterpenes, terpene compounds that contain 15 carbon atoms (diesel fuel typically contains 10 to 24 carbon atoms).

"Sesquiterpenes have a high-energy content and physicochemical properties similar to diesel and jet fuels," Lee says. "Although plants are the natural source of terpene compounds, engineered microbial platforms would be the most convenient and cost-effective approach for large-scale production of advanced biofuels."

In earlier work, Lee and his group engineered a new mevalonate pathway (a metabolic reaction critical to biosynthesis) in both E. coli and S. cerevisiae that resulted in these two microorganisms over-producing a chemical compound called farnesyl diphosphate (FPP), which can be treated with enzymes to synthesize a desired terpene. In this latest work, Lee and his group used that mevalonate pathway to create bisabolene, which is a precursor to bisabolane.

"We proposed that the generality of the microbial FPP overproduction platforms would allow for the biosynthesis of sesquiterpenes," Lee says. "Through multiple rounds of large-scale preparation in shake flasks, we were able to prepare approximately 20 milliliters of biosynthetic bisabolene, which we then hydrogenated to produce bisabolane."

When they began this work, Lee and his colleagues did not know whether bisabolane could be used as a biofuel, but they targeted it on the basis of its chemical structure. Their first step was to perform fuel property tests on commercially available bisabolene, which comes as part of a mixture of compounds. Convinced they were onto something, the researchers then used biosynthesis to extract pure biosynthetic bisabolene from microbial cultures for hydrogenation into bisabolane. Subsequent fuel property tests on the bisabolane were again promising.

"Bisabolane has properties almost identical to D2 diesel but its branched and cyclic chemical structure gives it much lower freezing and cloud points, which should be advantageous for use as a fuel," Lee says. "Once we confirmed that bisabolane could be a good fuel, we designed a mevalonate pathway to produce the precursor, bisabolene. This was basically the same platform used to produce the anti-malarial drug artemisinin except that we introduced a terpene synthase and further engineered the pathway to improve the bisabolene yield both in E. coli and yeast."

Lee and his colleagues are now preparing to make gallons of bisabolane for tests in actual diesel engines, using the new fermentation facilities at Berkeley Lab's Advanced Biofuels Process Demonstration Unit. The ABPDU is a 15,000 square-foot state-of-the art facility, located in Emeryville, California, designed to help expedite the commercialization of advanced next-generation biofuels by providing industry-scale test beds for discoveries made in the laboratory.

"Once the complete fuel properties of hydrogenated biosynthetic bisabolene can be obtained, we'll be able to do an economic analysis that takes into consideration production variables such as the cost and type of feedstock, biomass depolymerization method, and the microbial yield of biofuel," Lee says. "We will also be able to estimate the impact of byproducts present in the hydrogenated commercial bisabolene, such as farnesane and aromatized bisabolene."

Ultimately, Lee and his colleagues would like to replace the chemical processing step of bisabolene hydrogenation with an alkene reductase enzyme engineered into the E. coli and yeast so that all of the chemistry is performed within the microbes.

"Enzymatic hydrogenation of this type of molecule is a very challenging project and will be a long term goal," Lee says. "Our near-term goal is to develop strains of E. coli and yeast for use in commercial-scale fermenters. Also, we will be investigating the use of sugars from biomass as a source of carbon for producing bisabolene."

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Pamela P. Peralta-Yahya, Mario Ouellet, Rossana Chan, Aindrila Mukhopadhyay, Jay D. Keasling, Taek Soon Lee. Identification and microbial production of a terpene-based advanced biofuel. Nature Communications, 2011; 2: 483 DOI: 10.1038/ncomms1494

New metal hydride clusters provide insights into hydrogen storage

A study published by researchers at the RIKEN Advanced Science Institute (ASI) has shed first-ever light on a class of heterometallic molecular structures whose unique features point the way to breakthroughs in the development of lightweight fuel cell technology. The structures contain a previously-unexplored combination of rare-earth and d-transition metals ideally suited to the compact storage of hydrogen.

The most abundant element in the universe, hydrogen holds great promise as a source of clean, renewable energy, producing nothing but water as a byproduct and thus avoiding the environmental dangers associated with existing mainstream energy sources. Broad adoption of hydrogen, however, has stalled because in its natural gaseous state, the element simply takes up too much space to store and transport efficiently.

One way to solve this problem is to use metal hydrides, metallic compounds that incorporate hydrogen atoms, as a storage medium for hydrogen. In this technique, the metal hydrides bind to hydrogen to produce a solid one thousand times or more smaller than the original hydrogen gas. The hydrogen can then later be released from the solid by heating it to a given temperature.

The new heterometallic hydride clusters synthesized by the RIKEN researchers use rare-earth and d-transition metals as building blocks and exploit the advantages of both. Rare earth metal hydrides remove one major obstacle by enabling analysis using X-ray diffraction, a technique which is infeasible for most other metal hydrides -- offering unique insights into underlying reaction processes involved. Rare earth metal hydrides on their own, however, do not undergo reversible hydrogen addition and release, the cornerstone of hydrogen storage. This becomes possible through the addition of a d-transition metal, in this case tungsten (W) or molybdenum (Mo).

While rare-earth / d-transition metal-type metallic hydride complexes have been studied in the past, the current research is the first to explore complexes with multiple rare earth atoms of the form Ln4MHn and with well-defined structures (Ln = a rare-earth metal such as yttrium, M = a d-transition metal, either tungsten or molybdenum, and H = hydrogen). In a paper in Nature Chemistry, the researchers show that these complexes exhibit unique reactivity properties, pointing the way to new hydrogen storage techniques and promising environmentally-friendly solutions to today's pressing energy needs.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by RIKEN.

Journal Reference:

Takanori Shima, Yi Luo, Timothy Stewart, Robert Bau, Garry J. McIntyre, Sax A. Mason, Zhaomin Hou. Molecular heterometallic hydride clusters composed of rare-earth and d-transition metals. Nature Chemistry, 2011; DOI: 10.1038/NCHEM.1147

Researchers use carbon nanotubes to make solar cells affordable, flexible

Researchers from Northwestern University have developed a carbon-based material that could revolutionize the way solar power is harvested. The new solar cell material -- a transparent conductor made of carbon nanotubes -- provides an alternative to current technology, which is mechanically brittle and reliant on a relatively rare mineral.

Due to Earth's abundance of carbon, carbon nanotubes have the potential to boost the long-term viability of solar power by providing a cost-efficient option as demand for the technology increases. In addition, the material's mechanical flexibility could allow solar cells to be integrated into fabrics and clothing, enabling portable energy supplies that could impact everything from personal electronics to military operations.

The research, headed by Mark C. Hersam, professor of materials science and engineering and professor of chemistry, and Tobin J. Marks, Vladimir N. Ipatieff Professor of Catalytic Chemistry and professor of materials science and engineering, is featured on the cover of the October 2011 issue of Advanced Energy Materials, a new journal that specializes in science about materials used in energy applications.

Solar cells are composed of several layers, including a transparent conductor layer that allows light to pass into the cell and electricity to pass out; for both these actions to occur, the conductor must be both electrically conductive and also optically transparent. Few materials concurrently possess both of these properties.

Currently, indium tin oxide is the dominant material used in transparent conductor applications, but the material has two potential limitations. Indium tin oxide is mechanically brittle, which precludes its use in applications that require mechanical flexibility. In addition, Indium tin oxide relies on the relatively rare element indium, so the projected increased demand for solar cells could push the price of indium to problematically high levels.

"If solar technology really becomes widespread, as everyone hopes it will, we will likely have a crisis in the supply of indium," Hersam said. "There's a great desire to identify materials -- especially earth-abundant elements like carbon -- that can take indium's place in solar technology."

Hersam and Marks' team has created an alternative to indium tin oxide using single-walled carbon nanotubes, tiny, hollow cylinders of carbon just one nanometer in diameter.

The researchers have gone further to determine the type of nanotube that is most effective in transparent conductors. Nanotubes' properties vary depending on their diameter and their chiral angle, the angle that describes the arrangement of carbon atoms along the length of the nanotube. These properties determine two types of nanotubes: metallic and semiconducting.

Metallic nanotubes, the researchers found, are 50 times more effective than semiconducting ones when used as transparent conductors in organic solar cells.

"We have now identified precisely the type of carbon nanotube that should be used in this application," Hersam said.

Because carbon nanotubes are flexible, as opposed to the brittle indium tin oxide, the researchers' findings could pave the way for many new applications in solar cells. For example, the military could incorporate the flexible solar cells into tent material to provide solar power directly to soldiers in the field, or the cells could be integrated into clothing, backpacks, or purses for wearable electronics.

"With this mechanically flexible technology, it's much easier to imagine integrating solar technology into everyday life, rather than carrying around a large, inflexible solar cell," Hersam said.

Researchers are now examining other layers of the solar cell to explore also replacing these with carbon-based nanomaterials.

Besides Hersam and Marks, other authors include Timothy P. Tyler, Ryan E. Brock, and Hunter J. Karmel. This work was supported by the Argonne Northwestern-Northwestern Solar Energy Research Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Northwestern University, via EurekAlert!, a service of AAAS.

Journal Reference:

Timothy P. Tyler, Ryan E. Brock, Hunter J. Karmel, Tobin J. Marks, Mark C. Hersam. Organic Solar Cell Characterization: Electronically Monodisperse Single-Walled Carbon Nanotube Thin Films as Transparent Conducting Anodes in Organic Photovoltaic Devices (Adv. Energy Mater. 5/2011). Advanced Energy Materials, 2011; 1 (5): 701 DOI: 10.1002/aenm.201190021

Sneaking up on the glassy transition of water

Researchers claim to have settled a long-standing debate over the exact temperature at which water transforms into an exotic glass-like substance believed to be present in comets and other icy objects in the outer solar system, as well as in the coldest regions of Earth's atmosphere.

Rapid cooling of ordinary water or compression of ordinary ice: either of these can transform normal H2O into an exotic substance that resembles glass in its transparency, brittleness, hardness, and luster. Unlike everyday ice, which has a highly organized crystalline structure, this glass-like material's molecules are arranged in a random, disorganized way. Scientists have studied glassy water for decades, but the exact temperature at which water acquires glass-like properties has been the subject of heated debate for years, due to the difficulty of manipulating pure glassy water in laboratories.

Now, in a paper published in the AIP's Journal of Chemical Physics, physicists from the University of Pisa and the Consiglio Nazionale delle Ricerche at the Institute for Chemical-Physical Processes (CNR-IPCF) in Pisa, Italy, claim to have put an end to the controversy. Unlike previous attempts in which scientists tried to measure the transition temperature directly, the CNR team "snuck up" on the answer by inferring the temperature from a thorough study of the dynamics of water. They examined water's behavior in bulk and at the nano-scale, at high temperatures and low, combining their own experimental results with 15 decades' worth of research by colleagues.

They also measured the glass transition temperature and the molecular behavior of water that had been doped with other materials, and used this information to set lower and upper boundaries on the transition temperature for pure water. Taken together, their evidence points to a magic number of approximately 136 Kelvin (-137 Celsius). The authors say their work supports traditional views of this phenomenon and refutes recent claims that the transition is above 160 Kelvin (-113 Celsius). The research could find uses in technology associated with food science and the cryopreservation of biological materials, as well as in the study of water in comets and on the surface of planets.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

S. Capaccioli, K. L. Ngai. Resolving the controversy on the glass transition temperature of water? The Journal of Chemical Physics, 2011; 135 (10): 104504 DOI: 10.1063/1.3633242