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Tuesday, 25 August 2015

How we know what lies at Earth’s core

Humans have been all over the Earth. We've conquered the lands, flown through the air and dived to the deepest trenches in the ocean. We've even been to the Moon. But we've never been to the planet's core.

We haven't even come close. The central point of the Earth is over 6,000km down, and even the outermost part of the core is nearly 3,000 km below our feet. The deepest hole we've ever created on the surface is the Kola Superdeep Borehole in Russia, and it only goes down a pitiful 12.3 km.

All the familiar events on Earth also happen close to the surface. The lava that spews from volcanoes first melts just a few hundred kilometres down. Even diamonds, which need extreme heat and pressure to form, originate in rocks less than 500km deep.

What's down below all that is shrouded in mystery. It seems unfathomable. And yet, we know a surprising amount about the core. We even have some idea about how it formed billions of years ago – all without a single physical sample. This is how the core was revealed.

One good way to start is to think about the mass of the Earth, says Simon Redfern of the University of Cambridge in the UK.

We can estimate Earth's mass by observing the effect of the planet's gravity on objects at the surface. It turns out that the mass of the Earth is 5.9 sextillion tonnes: that's 59 followed by 20 zeroes.

There's no sign of anything that massive at the surface.

"The density of the material at the Earth's surface is much lower than the 
average density of the whole Earth, so that tells us there's something much denser," says Redfern. "That's the first thing."

Essentially, most of the Earth's mass must be located towards the centre of the planet. The next step is to ask which heavy materials make up the core.

The answer here is that it's almost certainly made mostly of iron. The core is thought to be around 80% iron, though the exact figure is up for debate.

The main evidence for this is the huge amount of iron in the universe around us. It is one of the ten most common elements in our galaxy, and is frequently found in meteorites.

Given how much there is of it, iron is much less common at the surface of the Earth than we might expect. So the theory is that when Earth formed 4.5 billion years ago, a lot of iron worked its way down to the core.

That's where most of the mass is, and it's where most of the iron must be too. Iron is a relatively dense element under normal conditions, and under the extreme pressure at the Earth's core it would be crushed to an even higher density, so an iron core would account for all that missing mass.

But wait a minute. How did that iron get down there in the first place?
The iron must have somehow gravitated – literally – towards the centre of the Earth. But it's not immediately obvious how.

Most of the rest of the Earth is made up of rocks called silicates, and molten iron struggles to travel through them. Rather like how water on a greasy surface forms droplets, the iron clings to itself in little reservoirs, refusing to spread out and flow.

A possible solution was discovered in 2013 by Wendy Mao of Stanford University in California and her colleagues. They wondered what happened when the iron and silicate were both exposed to extreme pressure, as happens deep in the earth.

By pinching both substances extremely tightly using diamonds, they were able to force molten iron through silicate.

"The pressure actually changes the properties of how iron interacts with the silicate," says Mao. "At higher pressures a 'melt network' is formed."

This suggests the iron was gradually squeezed down through the rocks of the Earth over millions of years, until it reached the core.

At this point you might be wondering how we know the size of the core. What makes scientists think it begins 3000km down? There's a one-word answer: seismology.

When an earthquake happens, it sends shockwaves throughout the planet. Seismologists record these vibrations. It's as if we hit one side of the planet with a gigantic hammer, and listened on the other side for the noise.

"There was a Chilean earthquake in the 1960s that generated a huge amount of data," says Redfern. "All the seismic stations dotted all over the Earth recorded the arrival of the tremors from that earthquake."

Depending on the route those vibrations take, they pass through different bits of the Earth, and this affects how they "sound" at the other end.

Early in the history of seismology, it was realised that some vibrations were going missing. These "S-waves" were expected to show up on one side of the Earth after originating on the other, but there was no sign of them.

The reason for this was simple. S-waves can only reverberate through solid material, and can't make it through liquid.

They must have come up against something molten in the centre of the Earth. By mapping the S-waves' paths, it turned out that rocks became liquid around 3000km down.

That suggested the entire core was molten. But seismology had another surprise in store.

In the 1930s, a Danish seismologist named Inge Lehmann noticed that another kind of waves, called P-waves, unexpectedly travelled through the core and could be detected on the other side of the planet.

She came up with a surprising explanation: the core is divided into two layers. The "inner" core, which begins around 5,000km down, was actually solid. It was only the "outer" core above it that was molten.

Lehmann's idea was eventually confirmed in 1970, when more sensitive seismographs found that P-waves really were travelling through the core and, in some cases, being deflected off it at angles. Sure enough, they still ended up on the other side of the planet.

It's not just earthquakes that sent useful shockwaves through the Earth. In fact, seismology owes a lot of its success to the development of nuclear weapons.

A nuclear detonation also creates waves in the ground, so nations use seismology to listen out for weapons tests. During the Cold War this was seen as hugely important, so seismologists like Lehmann got a lot of encouragement.

Rival countries found out about each other's nuclear capabilities and along the way we learned more and more about the core of the Earth. Seismology is still used to detect nuclear detonations today.

We can now draw a rough picture of the Earth's structure. There is a molten outer core, which begins roughly halfway to the planet's centre, and within it is the solid inner core with a diameter of 1,220 km.

But there is a lot more to try and tease out, especially about the inner core. For starters, how hot is it?

This turns out to be quite tricky to determine, and baffled scientists until quite recently, says Lidunka Vočadlo of University College London in the UK. We can't put a thermometer down there, so the only solution is to create the correct crushing pressure in the lab.

In 2013 a team of French researchers produced the best estimate to date. They subjected pure iron to pressures a little over half that at the core, and extrapolated from there. They concluded that the melting point of pure iron at core temperatures is around 6,230 °C. The presence of other materials would bring the core's melting point down a bit, to around 6,000 °C. But that's still as hot as the surface of the Sun.

A bit like a toasty jacket potato, Earth's core has stayed warm thanks to heat retained from the formation of the planet. It also gets heat from friction as denser materials shift around, as well as from the decay of radioactive elements. Still, it is cooling by about 100 °C every billion years.

Knowing the temperature is useful, because it affects the speed at which vibrations travel through the core. That is handy, because there is something odd about the vibrations.

P-waves travel unexpectedly slowly as they go through the inner core – slower than they would if it was made of pure iron.

"Wave velocities that the seismologists measure in earthquakes and whatnot are significantly lower [than] anything that we measure in an experiment or calculate on a computer," says Vočadlo. "Nobody as yet knows why that is."

That suggests there is another material in the mix.

It could well be another metal, called nickel. But scientists have estimated how seismic waves would travel through an iron-nickel alloy, and it doesn't quite fit the readings either.

Vočadlo and her colleagues are now considering whether there might be other elements down there too, like sulphur and silicon. So far, no-one has been able to come up with a theory for the inner core's composition that satisfies everyone. It's a Cinderella problem: no shoe will quite fit.

Vočadlo is trying to simulate the materials of the inner core on a computer. She hopes to find a combination of materials, temperatures and pressures that would slow down the seismic waves by the right amount.

She says the secret might lie in the fact that the inner core is nearly at its melting point. As a result, the precise properties of the materials might be different from what they would be if they were safely solid.

That could explain why the seismic waves pass through more slowly than expected.

"If that's the real effect, we would be able to reconcile the mineral physics results with the seismological results," says Vocadlo. "People have not been able to do that yet."

There are plenty of riddles about the earth's core still to solve. But without ever digging to those impossible depths, scientists have figured out a great deal about what is happening thousands of kilometres beneath us.

Those hidden processes in the depths of the Earth are crucial to our daily lives, in a way many of us don't realise.

Earth has a powerful magnetic field, and that is all thanks to the partially molten core. The constant movement of molten iron creates an electrical current inside the planet, and that in turn generates a magnetic field that reaches far out into space.

The magnetic field helps to shield us from harmful solar radiation. If the core of the Earth wasn't the way it is, there would be no magnetic field, and we would have all sorts of problems to contend with.

None of us will ever set eyes on the core, but it's good to know it's there.

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Wednesday, 19 August 2015

Paleobotanist identifies what could be the mythical 'first flower'

Indiana University paleobotanist David Dilcher and colleagues in Europe have identified a 125 million- to 130 million-year-old freshwater plant as one of earliest flowering plants on Earth.

The finding, reported Aug. 17 in the Proceedings of the National Academy of Sciences, represents a major change in the presumed form of one of the planet's earliest flowers, known as angiosperms.

"This discovery raises significant questions about the early evolutionary history of flowering plants, as well as the role of these plants in the evolution of other plant and animal life," said Dilcher, an emeritus professor in the IU Bloomington College of Arts and Sciences' Department of Geological Sciences.

The aquatic plant, Montsechia vidalii, once grew abundantly in freshwater lakes in what are now mountainous regions in Spain. Fossils of the plant were first discovered more than 100 years ago in the limestone deposits of the Iberian Range in central Spain and in the Montsec Range of the Pyrenees, near the country's border with France.

A large intact specimen of the fossil, Montsechia.Credit: David Dilcher 
Also previously proposed as one of the earliest flowers is Archaefructus sinensis, an aquatic plant found in China.

"A 'first flower' is technically a myth, like the 'first human,'" said Dilcher, an internationally recognized expert on angiosperm anatomy and morphology who has studied the rise and spread of flowering plants for decades. "But based on this new analysis, we know now that Montsechia is contemporaneous, if not more ancient, than Archaefructus."

He also asserted that the fossils used in the study were "poorly understood and even misinterpreted" during previous analyses.

"The reinterpretation of these fossils provides a fascinating new perspective on a major mystery in plant biology," said Donald H. Les, a professor of ecology and evolutionary biology at the University of Connecticut, who is the author of a commentary on the discovery in the journal PNAS. "David's work is truly an important contribution to the continued quest to unravel the evolutionary and ecological events that accompanied the rise of flowering plants to global prominence."

The conclusions are based upon careful analyses of more than 1,000 fossilized remains of Montsechia, whose stems and leaf structures were coaxed from stone by applying hydrochloric acid on a drop-by-drop basis. The plant's cuticles - the protective film covering the leaves that reveals their shape - were also carefully bleached using a mixture of nitric acid and potassium chlorate.

Examination of the specimens was conducted under a stereomicroscope, light microscope and scanning electron microscope.

The age of the plant at 125 million to 130 million years is based upon comparisons to other fossils in the same area, notably the freshwater algae charophytes, which places Montsechia in the Barremian age of the early Cretaceous period, making this flowering plant a contemporary of dinosaurs such as the brachiosaurus and iguanodon.

The precise, painstaking analysis of fossilized structures remains crucial to paleobotany, in contrast to other biological fields, due to the current inability to know the molecular characters of ancient plants from millions of years ago, Dilcher said.

This careful examination was particularly important to Montsechia since most modern observers might not even recognize the fossil as a flowering plant.

"Montsechia possesses no obvious 'flower parts,' such as petals or nectar-producing structures for attracting insects, and lives out its entire life cycle under water," he said. "The fruit contains a single seed" -- the defining characteristic of an angiosperm -- "which is borne upside down."

In terms of appearance, Dilcher said, Montsechia resembles its most modern descendent, identified in the study as Ceratophyllum. Also known as coontails or hornworts, Ceratophyllum is a dark green aquatic plant whose coarse, tufty leaves make it a popular decoration in modern aquariums and koi ponds.

Next up, Dilcher and colleagues want to understand more about the species connecting Montsechia and Ceratophyllum, as well as delve deeper into when precisely other species of angiosperms branched off from their ancient forefathers.

"There's still much to be discovered about how a few early species of seed-bearing plants eventually gave rise to the enormous, and beautiful, variety of flowers that now populate nearly every environment on Earth," he said.

Story Source:

The above post is reprinted from materials provided by Indiana University. Note: Materials may be edited for content and length.

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Wednesday, 12 August 2015

On this day in history – the first antiseptic operation was performed

In 1865, Dr. Joseph Lister became the first surgeon to perform an antiseptic operation by liberal use of carbolic acid (phenol) as a disinfectant. He had studied Louis Pasteur's germ theory of disease, that infections are caused by bacteria.


Lister knew carbolic acid had been effective in municipal use for treating sewage, and decided to try using it to kill germs that would otherwise infect wounds. He poured it on bandages, ligatures, instruments and directly on the wound and hands.

His first patient to benefit from this procedure was James Greenlees, age 12, whose broken leg was treated after being run over by a cart. The dressing was soaked with carbolic acid and linseed oil. The wound healed without infection. Lister continued his protocol of hygiene, and reduced the surgical death rate from 45% to 15%.

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Wednesday, 5 August 2015

Volcanic rocks resembling Roman concrete explain record uplift in Italian caldera

The discovery of a fiber-reinforced, concrete-like rock formed in the depths of a dormant supervolcano could help explain the unusual ground swelling that led to the evacuation of an Italian port city and inspire durable building materials in the future, Stanford scientists say.

The "natural concrete" at the Campi Flegrei volcano is similar to Roman concrete, a legendary compound invented by the Romans and used to construct the Pantheon, the Coliseum, and ancient shipping ports throughout the Mediterranean.

"This implies the existence of a natural process in the subsurface of Campi Flegrei that is similar to the one that is used to produce concrete," said Tiziana Vanorio, an experimental geophysicist at Stanford's School of Earth, Energy & Environmental Sciences.

Campi Flegrei lies at the center of a large depression, or caldera, that is pockmarked by craters formed during past eruptions, the last of which occurred nearly 500 years ago. Nestled within this caldera is the colorful port city of Pozzuoli, which was founded in 600 B.C. by the Greeks and called "Puteoli" by the Romans.

Beginning in 1982, the ground beneath Pozzuoli began rising at an alarming rate. Within a two-year span, the uplift exceeded six feet-an amount unprecedented anywhere in the world. "The rising sea bottom rendered the Bay of Pozzuoli too shallow for large craft," Vanorio said.

Making matters worse, the ground swelling was accompanied by swarms of micro-earthquakes. Many of the tremors were too small to be felt, but when a magnitude 4 quake juddered Pozzuoli, officials evacuated the city's historic downtown. Pozzuoli became a ghost town overnight.

A teenager at the time, Vanorio was among the approximately 40,000 residents forced to flee Pozzuoli and settle in towns scattered between Naples and Rome. The event made an impression on the young Vanorio, and inspired her interests in the geosciences. Now an assistant professor at Stanford, Vanorio decided to apply her knowledge about how rocks in the deep Earth respond to mechanical and chemical changes to investigate how the ground beneath Pozzuoli was able to withstand so much warping before cracking and setting off micro-earthquakes.

"Ground swelling occurs at other calderas such as Yellowstone or Long Valley in the United States, but never to this degree, and it usually requires far less uplift to trigger earthquakes at other places," Vanorio said. "At Campi Flegrei, the micro-earthquakes were delayed by months despite really large ground deformations."

To understand why the surface of the caldera was able to accommodate incredible strain without suddenly cracking, Vanorio and a post-doctoral associate, Waruntorn Kanitpanyacharoen, studied rock cores from the region. In the early 1980s, a deep drilling program probed the active geothermal system of Campi Flegrei to a depth of about 2 miles. When the pair analyzed the rock samples, they discovered that Campi Flegrei's caprock-a hard rock layer located near the caldera's surface-is rich in pozzolana, or volcanic ash from the region.

The scientists also noticed that the caprock contained tobermorite and ettringite-fibrous minerals that are also found in humanmade concrete. These minerals would have made Campi Flegrei's caprock more ductile, and their presence explains why the ground beneath Pozzuoli was able to withstand significant bending before breaking and shearing. But how did tobermorite and ettringite come to form in the caprock?

Once again, the drill cores provided the crucial clue. The samples showed that the deep basement of the caldera-the "wall" of the bowl-like depression-consisted of carbonate-bearing rocks similar to limestone, and that interspersed within the carbonate rocks was a needle-shaped mineral called actinolite.

"The actinolite was the key to understanding all of the other chemical reactions that had to take place to form the natural cement at Campi Flegrei," said Kanitpanyacharoen, who is now at Chulalongkorn University in Thailand.

From the actinolite and graphite, the scientists deduced that a chemical reaction called decarbonation was occurring beneath Campi Flegrei. They believe that the combination of heat and circulating mineral-rich waters decarbonates the deep basement, prompting the formation of actinolite as well as carbon dioxide gas. 

As the CO2 mixes with calcium-carbonate and hydrogen in the basement rocks, it triggers a chemical cascade that produces several compounds, one of which is calcium hydroxide. Calcium hydroxide, also known as portlandite or hydrated lime, is one of the two key ingredients in humanmade concrete, including Roman concrete. Circulating geothermal fluids transport this naturally occurring lime up to shallower depths, where it combines with the pozzolana ash in the caprock to form an impenetrable, concrete-like rock capable of withstanding very strong forces.

"This is the same chemical reaction that the ancient Romans unwittingly exploited to create their famous concrete, but in Campi Flegrei it happens naturally," Vanorio said.

In fact, Vanorio suspects that the inspiration for Roman concrete came from observing interactions between the volcanic ash at Pozzuoli and seawater in the region. The Roman philosopher Seneca, for example, noted that the "dust at Puteoli becomes stone if it touches water."

"The Romans were keen observers of the natural world and fine empiricists," Vanorio said. "Seneca, and before him Vitruvius, understood that there was something special about the ash at Pozzuoli, and the Romans used the pozzolana to create their own concrete, albeit with a different source of lime."

Pozzuoli was the main commercial and military port for the Roman Empire, and it was common for ships to use pozzolana as ballast while trading grain from the eastern Mediterranean. As a result of this practice, volcanic ash from Campi Flegrei-and the use of Roman concrete-spread across the ancient world. Archeologists have recently found that piers in Alexandria, Caesarea, and Cyprus are all made from Roman concrete and have pozzolana as a primary ingredient.

Interestingly, the same chemical reaction that is responsible for the unique properties of the Campi Flegrei's caprock can also trigger its downfall. If too much decarbonation occurs-as might happen if a large amount of saltwater, or brine, gets injected into the system-an excess of carbon dioxide, methane and steam is produced. As these gases rise toward the surface, they bump up against the natural cement layer, warping the caprock. This is what lifted Pozzuoli in the 1980s. When strain from the pressure buildup exceeded the strength of the caprock, the rock sheared and cracked, setting off swarms of micro-earthquakes. As pent-up gases and fluids vent into the atmosphere, the ground swelling subsided. Vanorio and Kanitpanyacharoen suspect that as more calcium hydroxide was produced at depth and transported to the surface, the damaged caprock was slowly repaired, its cracks "healed" as more natural cement was produced.

Vanorio believes the conditions and processes responsible for the exceptional rock properties at Campi Flegrei could be present at other calderas around the world. A better understanding of the conditions and processes that formed Campi Flegrei's caprock could also allow scientists to recreate it in the lab, and perhaps even improve upon it to engineer more durable and resilient concretes that are better able to withstand large stresses and shaking, or to heal themselves after damage.

"There is a need for eco-friendly materials and concretes that can accommodate stresses more easily," Vanorio said. "For example, extracting natural gas by hydraulic fracturing can cause rapid stress changes that cause concrete well casings to fail and lead to gas leaks and water contamination."

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Wednesday, 29 July 2015

On this day in Science History: The First Iron Lung was Installed

In 1927, the first iron lung (electric respirator) was installed at Bellevue hospital in New York for the post war polio epidemic. The first iron lung was developed at Harvard University by Phillip Drinker and Louis Agassiz Shaw built with two vacuum cleaners.

The iron lung is a negative pressure machine which surrounds the patient's body except for the head, and alternates a negative atmospheric pressure with the ambient one, resulting in rhythmic expansion of the chest cage (and thus inhalation) in response to the negative extra thoracic pressure. During periods of ambient extrathoracic pressure, the lungs deflate.

Humans, like most animals, breathe by negative pressure breathing: the rib cage expands and the diaphragm contracts, expanding the chest cavity. This causes the pressure in the chest cavity to decrease, and the lungs expand to fill the space. This, in turn, causes the pressure of the air inside the lungs to decrease (it becomes negative, relative to the atmosphere), and air flows into the lungs from the atmosphere: inhalation. When the diaphragm relaxes, the reverse happens and the person exhales. If a person loses part or all of the ability to control the muscles involved, breathing becomes difficult or impossible.

The person using the iron lung is placed into the central chamber, a cylindrical steel drum. A door allowing the head and neck to remain free is then closed, forming a sealed, air-tight compartment enclosing the rest of the person's body. Pumps that control airflow periodically decrease and increase the air pressure within the chamber, and particularly, on the chest. When the pressure is below that within the lungs, the lungs expand and atmospheric pressure pushes air from outside the chamber in via the person's nose and airways to keep the lungs filled; when the pressure goes above that within the lungs, the reverse occurs, and air is expelled. In this manner, the iron lung mimics the physiological action of breathing: by periodically altering intrathoracic pressure, it causes air to flow in and out of the lungs. The iron lung is a form of non-invasive therapy.

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Thursday, 23 July 2015

On this day in Science History: The Last Fragments of Comet Shoemaker-Levy Struck Jupiter

In 1994, the last of the large fragments of the comet Shoemaker-Levy struck Jupiter (Fragment W).

This was a comet that broke apart, colliding with Jupiter and providing the first direct observation of an extraterrestrial collision of Solar System objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide. The collision provided new information about Jupiter and highlighted its role in reducing space debris in the inner Solar System.

"Shoemaker-Levy 9 on 1994-05-17" by NASA, ESA, and H. Weaver and E. Smith (STScI) - http://hubblesite.org/newscenter/archive/releases/1994/26/image/c/ (direct link). Licensed under Public Domain via Wikimedia Commons 

The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy.  Shoemaker–Levy 9, at the time captured by and orbiting Jupiter, was located on the night of March 24, 1993, in a photograph taken with the 40 cm (16 in) Schmidt telescope at the Palomar Observatory in California. It was the first comet observed to be orbiting a planet, and had probably been captured by the planet around 20 – 30 years earlier. 

Calculations showed that its unusual fragmented form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker–Levy 9 passed within Jupiter's Roche limit, and Jupiter's tidal forces had acted to pull apart the comet. The comet was later observed as a series of fragments ranging up to 2 km (1.2 mi) in diameter. These fragments collided with Jupiter's southern hemisphere between July 16 and July 22, 1994, at a speed of approximately 60 km/s (37 mi/s) or 216,000 km/h (134,000 mph). The prominent scars from the impacts were more easily visible than the Great Red Spot and persisted for many months.

Observers hoped that the impacts would give them a first glimpse of Jupiter beneath the cloud tops, as lower material was exposed by the comet fragments punching through the upper atmosphere. Spectroscopic studies revealed absorption lines in the Jovian spectrum due to diatomic sulfur (S2) and carbon disulfide (CS2), the first detection of either in Jupiter, and only the second detection of S2 in any astronomical object. Other molecules detected included ammonia (NH3) and hydrogen sulfide (H2S). The amount of sulfur implied by the quantities of these compounds was much greater than the amount that would be expected in a small cometary nucleus, showing that material from within Jupiter was being revealed. Oxygen-bearing molecules such as sulfur dioxide were not detected, to the surprise of astronomers.

As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with abundances consistent with what would be found in a cometary nucleus. While substantial water was detected spectroscopically, it was not as much as predicted beforehand, meaning that either the water layer thought to exist below the clouds was thinner than predicted, or that the cometary fragments did not penetrate deeply enough. The relatively low levels of water were later confirmed by Galileo's atmospheric probe, which explored Jupiter's atmosphere directly.

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Wednesday, 15 July 2015

Leaving on a biofueled jet plane

The problem is simple to understand. Molecules of carbon and other greenhouse gases absorb heat. The more greenhouse gases emitted into the atmosphere, the warmer the atmosphere becomes, exacerbating global climate change. Solving the problem is not so simple, especially with regards to aviation -- the source of two-percent of the annual greenhouse gas emissions from human activity. While biofuels have proven to be an effective, renewable, low-carbon alternative to gasoline and diesel, jet fuels pose unique challenges. These challenges have now been met with a new technique developed by researchers at the Energy Biosciences Institute (EBI), a partnership led by the University of California (UC) Berkeley that includes Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of Illinois at Urbana-Champaign, and the BP energy company.

"We've combined chemical catalysis with life-cycle greenhouse gas modeling to create a new process for producing bio-based aviation fuel as well as automotive lubricant base oils," says Alexis Bell, a chemical engineer with joint appointments at Berkeley Lab and UC Berkeley. "The recyclable catalysts we developed are capable of converting sugarcane biomass into a new class of aviation fuel and lubricants with superior cold-flow properties, density and viscosity that could achieve net life-cycle greenhouse gas savings of up to 80-percent." These challenges have now been met with a new technique developed by researchers at the Energy Biosciences Institute (EBI), a partnership led by the University of California (UC) Berkeley that includes Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of Illinois at Urbana-Champaign, and the BP energy company.

Alex Bell, a leading authority on catalysis in biofuels. Credit:Image courtesy of DOE/Lawrence Berkeley National Laboratory
Bell is one of three corresponding authors of a paper describing this research in the Proceedings of the National Academy of Sciences (PNAS). The paper is titled "Novel pathways for fuels and lubricants from biomass optimized using life-cycle greenhouse gas assessment." Corinne Scown, a research scientist with Berkeley Lab's Energy Analysis and Environmental Impacts Division, and Dean Toste, a chemist with joint appointments at Berkeley Lab and UC Berkeley, are the other two corresponding authors. Additional authors are are Madhesan Balakrishnan, Eric Sacia, Sanil Sreekumar, Gorkem Gunbas and Amit Gokhale.

The concentrations of carbon and other greenhouse gases in Earth's atmosphere are now at their highest levels in the past three million years, primarily as a result of the burning of petroleum and other fossil fuels. Biofuels synthesized from the sugars in plant biomass help mitigate climate change. However, jet fuels have stringent requirements that must be met.

"Jet fuels must be oxygen-free, have the right boiling point distribution and lubricity, and a very low pour point, meaning the fuel can't become gelatinous in the cold temperatures of the stratosphere," Bell says. "Biofuel solutions, such as farnesane, mixed directly with petroleum jet fuel have been tested, but offer only modest greenhouse gas reduction benefits. Ours is the first process to generate true drop-in aviation biofuels."

Scown cites the Intergovernmental Panel on Climate Change (IPCC) on the importance of drop-in aviation biofuels.

"In a 2014 report, the IPCC pointed out that drop-in biofuels are the only viable alternative to conventional jet fuels," she says. "If we want to reduce our dependence on petroleum, air travel is going to require renewable liquid fuels because batteries and fuel cells simply aren't practical."

The process developed at EBI can be used to selectively upgrade alkyl methyl ketones derived from sugarcane biomass into trimer condensates with better than 95-percent yields. These condensates are then hydro-deoxygenated into a new class of cycloalkane compounds that contain a cyclohexane ring and a quaternary carbon atom. These cycloalkane compounds can be tailored for the production of either jet fuel, or automotive lubricant base oils. Lubricant base oils can produce even more greenhouse gas emissions on a per-mass basis than petroleum-derived fuels if even a fraction of the lubricant is repurposed as fuel. The ability of the EBI process to yield jet fuel or lubricants should be a significant advantage for biorefineries.

"Sugarcane biorefineries today produce ethanol, sugar and electricity," says PNAS paper co-author Gokhale, a chemical engineer, who is managing the research project from BP's side. "Expanding the product slate to include aviation fuels and lubricant base oils could allow for operators to manage their market risks better, which is exactly how petrochemical refinery complexes operate today. Rather than optimize for one product, they try to optimize the overall product slate."

Adds Scown, "Another important advantage offered by our process is that it enables refineries to convert a portion of the bagasse, the fibrous residue that remains after juice is extracted from sugarcane stalk, into fuels and other products. The rest of the waste biomass can be combusted to produce process heat and electricity to operate the refinery." This new EBI process for making jet fuel and lubricants could also be used to make diesel and additives for gasoline as Gokhale explains.

"With some minimal modifications to both the catalysts and the reaction schemes we can produce drop-in diesel as well," he says. "We're planning further studies on this."

Although the goal of this study was to develop a strategy for the flexible production of jet fuels and lubricant base oils in a Brazilian sugarcane refinery, the strategy behind the process could also be applied to biomass from other non-food plants and agricultural waste that are fermented by genetically engineered microbes.

"Although there are some additional technical challenges associated with using sugars derived entirely from biomass feedstocks like Miscanthus and switchgrass, there is no fundamental reason why we could not produce similar outputs, albeit in different proportions," Scown says. "We expect that further research will make this option increasingly attractive."

In their PNAS paper the authors acknowledge that the commercial implementation of their proposed process would include financial implications that extend beyond greenhouse gas emission reductions but hold that there still important incentives to encourage investments.

"We've shown in this study that biorefineries can use inexpensive catalysts to produce a suite of hydrocarbon fuels and lubricants," Scown says. "By strategically piecing together biological and thermochemical processes, biorefineries can also operate without any fossil-derived inputs."

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