Nanotechnology; Co2 conversion to fuel.

[butterfly]

Nanotube tech transforms CO2 into fuel

Thursday, 26 March 2009 Eric Bland
Discovery News (http://dsc.discovery.com/news/news.html)
http://www.abc.net.au/reslib/200903/r353519_1623926.jpg (http://www.abc.net.au/reslib/200903/r353519_1623929.jpg) Instead of storing energy from the sun in batteries, the system will store it chemically (Source: iStockphoto)



Titanium oxide nanotubes powered by sunlight are turning carbon dioxide into methane, which could be used as a future energy source, say US scientists.

The nanotubes could dramatically reduce CO2 emissions into the atmosphere and reduce our need for fossil fuels.
"Right now there is lots of talk about burying carbon dioxide, which is ridiculous," says Craig Grimes of Pennsylvania State University (http://www.psu.edu/), who, along with Oomman Varghese, Maggie Paulose and Thomas LaTempa, co-authored a paper on the nanotubes in the journal Nano Letters (http://pubs.acs.org/journal/nalefd?cookieSet=1).
"Instead we can collect the waste out of the smoke stack, put it though a converter, and presto, use sunlight to change [CO2] back into fuel."
Splitting atoms

The nanotubes are arranged vertically, almost like empty honeycomb. Over the top of the nanotubes sits a thin, reddish-brown layer of copper oxide.
Both the copper and titanium oxide act as catalysts, speeding up reactions that take place naturally.
When sunlight hits the copper oxide, carbon dioxide is converted into carbon monoxide. When sunlight hits the titanium oxide, water molecules split apart.
The hydrogen freed from the water and the carbon freed from CO2 then recombine to create burnable methane, and the spare oxygen atoms pair up to create breathable oxygen.
The scientists have created thin membranes that cover either 25 or 100 square centimetres. So far, those membranes have produced an estimated 250 litres of methane, says Grimes.
Adding more light and CO2 creates more methane. Grimes estimates that focusing the light collected from 100 square metres onto one of the membranes would generate more than 500 litres of methane on a sunny day.
Chemical storage

This is solar power by another name, say Grimes and other scientists. Instead of storing electrons in batteries, Grimes' idea would store energy chemically.
That chemical energy could be used for many things. Methane stored in cylinders could be sold to consumers, much like propane is stored, sold, and used in outdoor grills or for gas stoves.
Coal-burning power plants could use the methane to heat water and generate more electricity.
One big advantage of methane over other hydrocarbons, like hydrogen gas, is that an infrastructure already exists for methane, says Kyoung-Shin Choi, a chemistry professor at Purdue University (http://www.purdue.edu/) who was not involved in the research.
"If you want to use hydrogen as an energy source in the future, you have to convert all the existing infrastructure," says Choi. "But we've been using methane for years, and can utilize all the infrastructure we already have."
"It's a clean and sustainable cycle as long as you have sun and water."
Whether the process is competitive commercially is still to be determined, says Grimes.
"Do we take that CO2 and bury it, or do we use sunlight to turn it back into fuel?" he says. "Today it's an even draw."


Admittedly I don't have much of an understanding of nanotechnology. Do people see this as viable?
Isn't methane 20 times more damaging to the environment in contrast to Co2? So presumably the technology uses larger amounts of Co2 in order to create it.

[ÑóẊîöʼn]

Admittedly I don't have much of an understanding of nanotechnology. Do people see this as viable?

I don't see why not. This is actually a fairly simple example of nanotechnology, which appears to use the greatly increased surface area offered by nanotubes to greatly increase an already-present catalysing effect.

It's not like they're promising molecule-sized robots that'll free everyone of labour.


Isn't methane 20 times more damaging to the environment in contrast to Co2? So presumably the technology uses larger amounts of Co2 in order to create it.Methane is a highly potent greenhouse gas, but in the Earth's atmosphere it has a half-life of seven years during which it breaks down into carbon dioxide and water.

The impression I got from the article was that the methane thus produced would be used as a fuel rather than simply a method of locking up carbon dioxide. Thus rather than being released into the atmosphere, it would be consumed and we'd only have to worry about it's daughter products.

[mikelepore]

No matter what you do chemically, it's a way to store energy, not produce it.

You can even choose a method that stores away your greenhouse gases, but on a later occasion they will come back out again.

Whatever you put in on one day is exactly what comes out on another day.

Hydrogen, storing your energy:
2 H2O + energy ---> 2 H2 + O2

Hydrogen, getting your energy back out:
2 H2 + O2 ---> 2 H2O + energy

Methane, storing your energy:
2 H2O + CO2 + energy ---> CH4 + 2 O2

Methane, getting your energy back out
CH4 + 2 O2 ---> 2 H2O + CO2 + energy

[ÑóẊîöʼn]

No matter what you do chemically, it's a way to store energy, not produce it.

Erm, didn't you read the article? The energy comes from sunlight, which converts carbon dioxide and water into methane which can be burned, producing water and carbon dioxide as reaction products, which can again be recombined using sunlight. The water and carbon dioxide cycle in this system is closed, but not the energy cycle.

[Picky Bugger]

The impression I got from the article was that the methane thus produced would be used as a fuel rather than simply a method of locking up carbon dioxide. Thus rather than being released into the atmosphere, it would be consumed and we'd only have to worry about it's daughter products.

I think you are right about this, it seems unlikely that people would be advocating the use of methane as a storage device over what would presumable be a large scale. Does anyone happen to know daughter products of burning methane would be? (I assume it will be burned)

It looks like a promising source of energy but once again it is variable in nature and dependent on an abundant but variable energy source at least for higher latitude countries. I am cautious about solar energy because it is possible that it will cause energy inequality across climates on a grand scale, energy trading is a convoluted business.

[ÑóẊîöʼn]

I think you are right about this, it seems unlikely that people would be advocating the use of methane as a storage device over what would presumable be a large scale. Does anyone happen to know daughter products of burning methane would be? (I assume it will be burned)

If I remember correctly, it's water and carbon dioxide, which can be recombined again into methane using solar energy as above.


It looks like a promising source of energy but once again it is variable in nature and dependent on an abundant but variable energy source at least for higher latitude countries. I am cautious about solar energy because it is possible that it will cause energy inequality across climates on a grand scale, energy trading is a convoluted business.

Which is why I think it's important to have a variety of energy sources, including nuclear.

[Picky Bugger]

Once again I agree but society has a way of centralising around the method that is cheapest before thinking about diversity or efficiency for example.

On another note I have a particular dislike for small scale Solar energy at the moment since the efficiency is on average about 15%, 30% being seen as very good over a 5 year period. It's just not good enough...

[Cult of Reason]

A problem I see with this (unless I was too rushed to read the article properly) is that the places where the methane would be used would not necessarily be the best places to produce it. Take a coal or methane burning power station in the UK, for example. The UK is not famed for having a sunny climate, so the effectiveness of these systems would be greatly reduced. Ideally you would want to have these systems all in the Sahara, so how would you transport the CO2 and water vapour? LArge pipelines parallel to the methane pipelines?

Also, what is the total conversion efficiency of the system? How much of the solar energy gets converted into chemical energy in the methane as opposed to chemical energy in the byproducts of O2 etc. and other losses? And when the methane is actually being used, how much of its stored energy is usefully harnessed as work, rather than lost as heat, etc., again?

I do not have these figures, and I am a little busy now, but concentrating solar thermal can have a conversion efficiency of 35%, and another 50% (otherwise wasted heat) can be used for desalination, for an efficiency, sort of, of 85% (though only if you actually want the water and if you can transport enough seawater). Also, a high-voltage direct current line from Libya to the UK would have an transport efficiency of about 90% (including the conversion from DC to AC), IIRC, meaning an efficiency of 31.5% when the energy enters the UK's National Grid. Because the UK's National Grid was mostly built in the 1960s with transformers that are below the standard of today, and because going from high voltage to safe voltage involves going through 5 sets of transformers, there is a loss of 8.5% (link here (http://resources.schoolscience.co.uk/CDA/16plus/copelech5pg2.html)), i.e. the National Grid is 91.5% efficient (the lower scores you often read about are including the efficiency of the power stations, which are inefficient, but they do not concern us here).

This means that, overall, 28.8% of the sunlight from Libya that hits the collectors would then be used by you as the end-user, thousands of kilometres away. If we consider only the electricity that the plants in Libya would output, the total efficiency of the transport would be about 82% efficient.

How does the "lifecycle" of the methane-stored energy compare with CST's 28.8% efficiency?

[Picky Bugger]

A problem I see with this (unless I was too rushed to read the article properly) is that the places where the methane would be used would not necessarily be the best places to produce it. Take a coal or methane burning power station in the UK, for example. The UK is not famed for having a sunny climate, so the effectiveness of these systems would be greatly reduced. Ideally you would want to have these systems all in the Sahara, so how would you transport the CO2 and water vapour? LArge pipelines parallel to the methane pipelines?

This goes back to my point about energy inequality but more so energy security, if the system is based in the Sahara then countries such as the UK will not want to use it as they are not guaranteed power etc. With cases such as oil this is tolerated because oil is necessary for everything we do, I cannot see a movement to this technology if it is centralised in Northern Africa.


This means that, overall, 28.8% of the sunlight from Libya that hits the collectors would then be used by you as the end-user, thousands of kilometres away. If we consider only the electricity that the plants in Libya would output, the total efficiency of the transport would be about 82% efficient.

Not a particularly efficient system on the whole especially at end use but of course efficiency rises as the technology develops. The notion of piping the energy from Libya may not be needed if the efficiency of the solar receptors can be relatively low, the solar energy levels in the UK may be adequate and it doesn't say that they aren't in the article.

It could be a decent source of energy for newly industrialised nations but i'm guessing that the technology will not be cheap.

Not sure about the life cycle, I had a look on the net but could not find anything, at a guess it would probably be similar if not lower to CST.

[Cult of Reason]

Not a particularly efficient system on the whole especially at end use but of course efficiency rises as the technology develops.

Not efficient compared with what?


The notion of piping the energy from Libya may not be needed if the efficiency of the solar receptors can be relatively low, the solar energy levels in the UK may be adequate and it doesn't say that they aren't in the article.

I do not quite understand you, but assuming you mean "if the efficiency of the solar receptors is high":

Efficiency is not the only thing. It is also relevant to consider energy gain for energy invested and energy gain for area covered. It may be possible to have solar power in the UK, but a much larger area would have to be covered. Would you like to see the Midlands blanketed completely with these receptors? If the solar energy is gathered in Libya then we can use the countryside in the UK for food and so on, while the land in Libya is otherwise useless. The system as a whole is optimised if solar energy is gathered in Libya rather than the UK.

[Picky Bugger]

Not efficient compared with what?

At the moment it does not seem total efficient in itself never mind compared with other technologies. I don't have the figures for the other renewables or nuclear but they must be comparable if not greater and these remove the issue of security.


I do not quite understand you, but assuming you mean "if the efficiency of the solar receptors is high":

I meant was that the levels of solar power in the UK may be adequate to power the conversion. I did not necessarily mean that the receptors needed high efficiency but that an efficiency level of say 15% would be enough, granted in hotter countries the efficiency will be higher.

I can see that the technology is aimed towards this Libya - UK example but as I stated before the idea of energy security is very important, if there were pipelines spanning across Libya, Europe then the UK it would be difficult to protect the power supplies. In this case it would be extremely necessary to have a wide range of power production methods, until then it would be foolish to implement such a system.

[Elect Marx]

The link no longer goes to the article BTW.


A problem I see with this (unless I was too rushed to read the article properly) is that the places where the methane would be used would not necessarily be the best places to produce it. Take a coal or methane burning power station in the UK, for example. The UK is not famed for having a sunny climate, so the effectiveness of these systems would be greatly reduced. Ideally you would want to have these systems all in the Sahara, so how would you transport the CO2 and water vapour? LArge pipelines parallel to the methane pipelines?

Great point. Transportation would be a huge issue. I suspect transporting compressed/liquefied methane might be an option, or the hydrocarbons could simply be a way to convey energy in the process. You could convert the fuel to electricity and recycle the medium. The benefit of such a system is that you do not have to "burn" (might use some sort of fuel cell system) the methane immediately, allowing energy storage to be used as needed (Sunlight or not).


Also, what is the total conversion efficiency of the system? How much of the solar energy gets converted into chemical energy in the methane as opposed to chemical energy in the byproducts of O2 etc. and other losses? And when the methane is actually being used, how much of its stored energy is usefully harnessed as work, rather than lost as heat, etc., again

Exactly. We don't know if this is a viable process without these numbers. One benefit would be, that nanotech layers use very little material. I am not sure how much processing would be involved, or how effectively it can be done currently, but titanium and copper aren't extremely rare.

[butterfly]

I can see that the technology is aimed towards this Libya - UK example but as I stated before the idea of energy security is very important, if there were pipelines spanning across Libya, Europe then the UK it would be difficult to protect the power supplies. In this case it would be extremely necessary to have a wide range of power production methods, until then it would be foolish to implement such a system.
I would agree but no one is saying we should remain dependent on a single source of energy.
In terms of energy security, nuclear would face the same dilemma as it is dependent on resources from abroad as well.

[Picky Bugger]

I agree and it is valuable to have a range of power but with the current international model this method is unlikely to be seen as a viable option for many western countries.