Nitrogen-fixing aliens

Scientists hope that Titan, a moon of Saturn, with its nitrogen-rich atmosphere, could act as a model system for terrestrial chemistry before life began on our planet. Now, another step towards that goal has emerged as researchers at the University of Arizona have incorporated atmospheric nitrogen into organic macromolecules under conditions resembling those on Titan.

“Titan is so interesting because its nitrogen-dominated atmosphere and organic chemistry might give us a clue to the origin of life on our Earth,” explains Hiroshi Imanaka, who is an assistant research scientist in the UA’s Lunar and Planetary Laboratory. “Nitrogen is an essential element of life.” Titan looks orange through a telescope because its atmosphere is a rich smog of organic molecules. Particles in the smog could settle on the surface and be exposed to conditions that might eventually create life, said Imanaka.

Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)
Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)

Of course, nitrogen alone is not enough, nitrogen molecules must be converted to a chemically active form that can drive the necessary biochemical reactions that underpin biological systems.

Imanaka and Mark Smith converted a nitrogen-methane gas mixture similar to Titan’s atmosphere into a collection of nitrogen-containing organic molecules by irradiating the gas with high-energy ultraviolet light. The laboratory set-up was designed to mimic how solar radiation affects Titan’s atmosphere.

Most of the nitrogen simply formed solid compounds directly, rather than gaseous ones, explains Smith, whereas previous theories suggested that nitrogen would move from gaseous compounds to solid ones in stepwise process. But, those settling particles may not contain nitrogen at all. If some of the particles are the same nitrogen-containing organic molecules created by the UA team in the laboratory then it would suggest that conditions conducive to life might just exist on Titan, Smith says.

These and other laboratory observations help scientists planning future space missions to decide on what to look for on other worlds that might hint at life and what instruments should be developed to help in the search.

Links

Proc Natl Acad Sci, 2010, online
Mark A. Smith homepage
UA lunar and planetary laboratory

Craig Grimes – Recycling in the greenhouse

Could we use solar power to convert that troublesome greenhouse gas, carbon dioxide, into useful methane fuel for heating and electricity generation? According to research published in the journal Nano Letters that could be a real possibility.

The use of fossil fuels in transport and power generation has inadvertently pumped billions of tonnes of the greenhouse gas carbon dioxide into the atmosphere. Climate models suggest that the long-term impact could be to cause severe and deleterious climate change that will have an impact on us and future generations.

A proposed flow-through reactor for carbon dioxide conversion (Credit: Grimes Group)

A proposed flow-through reactor for carbon dioxide conversion (Credit: Grimes Group)

Now, Craig Grimes and colleagues, Oomman Varghese, Maggie Paulose and Thomas LaTempa, at Pennsylvania State University have devised an intriguing method for converting captured carbon dioxide into useful methane, a combustible fuel, using the energy of the sun.

The team has built a material based on a three-dimensional array of nitrogen-doped titania nanotubes coated with an ultrathin layer of a platinum or copper co-catalyst. Titania normally absorbs in the high-energy ultraviolet end of the electromagnetic spectrum. However, the presence of the co-catalyst shifts this absorption into the visible wavelengths associated with sunlight reaching the Earth’s surface.

A test batch reactor for producing methane from carbon dioxide (Credit: Grimes Group)

A test batch reactor for producing methane from carbon dioxide (Credit: Grimes Group)

The result is a highly efficient photocatalyst that absorbs sunlight and essentially adds this energy to carbon dioxide by converting it back into an energy-rich hydrocarbon.

Craig Grimes

Craig Grimes

To demonstrate proof of principle the team loaded their nanotube arrays into a stainless steel chamber filled with carbon dioxide and infused with water vapour. The chamber was left in direct outdoor sunlight for several hours during which time the carbon dioxide was transformed into methane and water released as a by-product. The team demonstrated that 160 microlitres of methane could be produced per hour by just one gram of nanotubes. This rate is twenty times higher than experiments carried out in the laboratory using pure ultraviolet light.

“Copper oxide and titanium dioxide are common materials,” Grimes says. “We can tune the reaction using platinum nanoparticles or ideally other, less expensive catalysts.” Grimes believes that the conversion process might readily be improved by several orders of magnitude, which could make the process economically feasible.

Capturing carbon dioxide from power stations and converting it into methane cheaply using solar power could improve the economics of carbon capture dramatically. Grimes also suggests that a similar system might also one day be possible for trapping and converting carbon dioxide from vehicle exhaust.

Further reading

Nano Lett., 2009, 9, 731-737
http://dx.doi.org/10.1021/nl803258p

Materials Research Institute homepage
http://www.mri.psu.edu

Craig Grimes spotlight
http://www.mri.psu.edu/articles/BC/faculty/CraigGrimes/index.asp

Suggested searches

greenhouse gases
carbon dioxide
methane
nanotubes

Climate change lifesaver

Adding lime to the oceans may help reverse the rise in atmospheric carbon dioxide, according to a report in the journal Chemistry & Industry. Petrochemicals giant Shell is pumping money into a feasibility study of the idea, which might one day reduce, if not reverse, the impact on climate change of fossil fuel use, the scheme’s proponents hope.

The theory, being developed as an open source concept under the name Cquestrate, suggests that adding lime (primarily calcium oxide) to seawater will increase its alkalinity and so boost the seawater’s ability to absorb carbon dioxide from the air. Moreover, it will reduce the water’s tendency to release the gas back into the air. However, until recently the idea was thought to be unworkable because of the expense of obtaining lime from limestone and the amount of carbon dioxide that would be released in the process. Additionally, there are issues associated with the macroscale chemical engineering that will be required to have a global effect.

Could pouring lime into the oceans be a climate change lifesaver? (Photo by David Bradley)

Could pouring lime into the oceans be a climate change lifesaver? (Photo by David Bradley)

We think it’s a promising idea, says Shell’s Gilles Bertherin, a coordinator on the project, There are potentially huge environmental benefits from addressing climate change – and adding calcium hydroxide to seawater will also mitigate the effects of ocean acidification, so it should have a positive impact on the marine environment.

Tim Kruger, a management consultant at London firm Corven, who previously worked for Shell, is the brains behind the plan to implement the lime process. He argues that it could be made workable by locating it in regions that have a combination of low-cost ‘stranded’ energy considered too remote to be economically viable to exploit – like flared natural gas or Solar energy in deserts – and that are rich in limestone, making it feasible for calcination to take place on site as it requires the strong heating of limestone.

Australia’s Nullarbor Plain visible as the smooth croissant shaped coastal region in this NASA satellite image (Credit Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

Australia’s Nullarbor Plain visible as the smooth croissant shaped coastal region in this NASA satellite image (Credit Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

Kruger says: There are many such places – for example, Australia’s Nullarbor Plain would be a prime location for this process, as it has 10000 cubic kilometres of limestone and soaks up roughly 20 megajoules per square metre of Solar irradiation every day. Kruger told Spotlight that to sequester several billion tonnes of carbon dioxide requires 1.5 cubic kilometres of limestone. Of course, the scheme ignores the environmental impact on pristine wilderness, such as the Nullarbor Plain.

Of course, the process of making lime generates carbon dioxide, but adding the lime to seawater absorbs almost twice as much carbon dioxide. The overall process is therefore carbon negative. This process has the potential to reverse the accumulation of carbon dioxide in the atmosphere, Kruger says. He believes it should be possible to reduce atmospheric carbon dioxide to pre-industrial levels. The oceans are already the world’s largest carbon sink, absorbing 2 billion tonnes of carbon every year. Increasing absorption ability by just a few percent could dramatically increase carbon dioxide uptake from the atmosphere. Klaus Lackner of Columbia University tentatively agrees, The theoretical carbon dioxide balance is roughly right…it is certainly worth thinking through carefully.

The fact that the concept is open source means that anyone with the will and the means could develop the required technology. However, it is likely to require vast tonnages of raw material, which must be mined and sourced and then spread into the oceans. So the question of it being carbon negative must be considered in detail taking into account the whole process lifecycle.

There are also issues of oceanic pH change in such a way as to interfere with the very ecosystems, including fragile coral reefs, that are already under threat from climate change. Researchers must investigate possible unforeseen outcomes with such a massive chemical experiment, especially, given the inconclusive and often negative results with other macro chemical engineering schemes, such as nitrogen control and iron seeding of the oceans.

With the hint of lime concept, a lot more theoretical work must be done before we plunge into a campaign to attempt to modify the oceans in this way. We’re looking at computer simulations of the process and will progress to small-scale laboratory tests first, Kruger told Spotlight, there’s certainly no intention to just dump lime into the oceans.

Further reading

Cquestrate
http://www.cquestrate.com

Misguided Meddling
https://www.sciencebase.com/science-blog/misguided-environmental-meddling.html

Shell
http://www.shell.com/

Suggested searches

carbon dioxide
climate change
carbon sequestration