March 08, 2009
Nanotubes For Photocatalysis Produce Methane
A cheap synthetic system that works better than plant photosynthesis for producing hydrocarbons from carbon dioxide, water, and sunlight might some day provide a great source of energy. Toward that end some Penn State researchers have advanced the state of the art for light-driven methane generation using titania nanotubes. I love to see this kind of advance.
Dual catalysts may be the key to efficiently turning carbon dioxide and water vapor into methane and other hydrocarbons using titania nanotubes and solar power, according to Penn State researchers.
Burning fossil fuels like oil, gas and coal release large amounts of carbon dioxide, a greenhouse gas, into the atmosphere. Rather than contribute to global climate change, producers could convert carbon dioxide to a wide variety of hydrocarbons, but this makes sense to do only when using solar energy.
"Recycling of carbon dioxide via conversion into a high energy-content fuel, suitable for use in the existing hydrocarbon-based energy infrastructure, is an attractive option, however the process is energy intense and useful only if a renewable energy source can be used for the purpose," the researchers note in a recent issue of Nano Letters.
Craig A. Grimes, professor of electrical engineering and his team used titanium dioxide nanotubes doped with nitrogen and coated with a thin layer of both copper and platinum to convert a mixture of carbon dioxide and water vapor to methane. Using outdoor, visible light, they reported a 20-times higher yield of methane than previously published attempts conducted in laboratory conditions using intense ultraviolet exposures.
This is still a laboratory-level advance. Industrial field use is still years away. But it is the sort of advance that could eventually provide a way to suck large amounts of carbon dioxide out of the atmosphere. Further enhancements to make longer chain hydrocarbons could yield synthetic hydrocarbon liquids for transportation.
One of the advantages of a synthetic replacement for photosynthesis is the ability to operate for a larger fraction of the year. March 21 and September 21 are halfway points between the shortest and longest days of the year. In the northern hemisphere March 21's photons drive far less photosynthesis than September 21's photons because plants are still in frozen state in the more northern areas (with a similar pattern in the southern hemisphere with swapped dates for spring and fall starts). The late winter and early spring photons could be harnessed sooner in a synthetic system that didn't require plant growth to create areas for capturing the photons. Also, a synthetic system could cover ground which currently can't support much plant life.
A synthetic system built to float far out to sea could absorb photons and do synthesis over area of the ocean that are too nutrient poor to support much microbial life. While such installations are too expensive today in the future nanoassemblers will drastically reduce the cost of construction of massive floating solar collecting synthetic hydrocarbon production ships.
Update: To clarify: Methane is a far more potent atmospheric warmer than carbon dioxide. So a synthetic methane synthesizer with a big leak in it would warm the planet. In fact, if one wanted to, say, prevent an ice age then synthetic methane producers with their output vented to the atmosphere would be one way to do it. On the other hand, if one's photochemical hydrocarbon synthesizer produced longer chain liquid hydrocarbons (gotta be longer than Hank Hill's propane in order to remain liquid) then the atmospheric warming risk would be eliminated. Since the longer chain hydrocarbons are far more desirable for transportation a method for generating them would be ideal.
But it is the sort of advance that could eventually provide a way to suck large amounts of carbon dioxide out of the atmosphere.
That's a little disingenuous. It replaces one greenhouse gas with a much stronger greenhouse gas--unless, of course, we burn it right back into the original greenhouse gas for no net change at all.
Photosynthesis maxes out at around 5% solar energy to biomass with some less credible claims going as high as 10%. Where is this "synthetic replacement for photosynthesis" and what sort of credibility can we assign to the number given?
I really think this is still at the lab stage. As for what efficiency they can achieve I think it is still too early to tell.
Do refer to a dictionary before posting. Was I lacking in candor? Did I post with prejudice or malice? Or did I just fail to mention that methane could leak if not handled properly?
Yes, you lacked candor. Only a little, but yes.
No, I just didn't wrench my brain to say everything I could possibly recall about methane. I do not cover every aspect of every topic every time I post about that topic. Try doing this yourself before you try second guessing motives that were not there.
I didn't say anything about your motives. I have no idea why you wrote something that lacked even a little candor. I only observed that you did. It appears what I wrote offended you, and I apologize for that. Offending you was not my intent, and even now, it's not entirely clear to me how I did so.
This technology doesn't suck anything out of anything. It uses solar energy to reduce a dense, inert greenhouse gas into a less dense, highly reactive greenhouse gas. As far as carbon sequestration goes, it doesn't really advance anything.
It would be perfectly candid, though, to say this technology is an important advance toward efficiently converting solar energy into carbon-neutral, transportable fuels. That advance offers just as much cause for excitement.
The purpose of creating methane here is unlikely to be solely as carbon sequestration, though I guess it could be done. Rather it is aimed, I presume, at the 'methanol economy' which would be like the 'hydrogen economy' and a substitute for the 'petroleum economy'.
That is, if this method scales up and provides industrial-quantity, cheaper-than-oil, methane, we could then use the methane to power cars and trucks, and provide methane fuel cells for cell phones, laptops, and other portable gear, which would get us around any possible lithium shortages. And methanol is easy enough to crack into lots of other things we typically source from petroleum.
Therefore, the CO2 story of methane must take into account the whole picture: not just the CO2 burning methane and its byproducts would create, but also the CO2 'saved' by not burning oil, gas, or coal. Since this method extracts CO2 from the atmosphere, burning the results would be 'carbon neutral' (or nearly so) and thus would, in the end, reduce the amount of additional CO2 that would otherwise have been delivered from burning oil natural gas and coal.
So it's unlikely to reduce the CO2 in the atmosphere; but it might well slow down the rate at which we are presently increasing the load.
What continues to strike me is just how new and hard it is to consider such advances in light of the total effects they might have on the total ecosystem. This is a totally new way of thinking, and we giant apes are not good at it -- yet.
Converting methane into methanol is harder than it sounds. Methanol usually comes from fermenting complex sugars like cellulose.
Randall is correct to suggest the methane might be the raw material for producing longer-chain alkanes. Perhaps other nano-materials will provide efficient means to capture solar energy for that purpose too. This advance then might form the first stage in a multi-stage reactor that converts solar energy directly into carbon-neutral gasoline or diesel fuel.
To a certain extent, the technology for creating longer-chain alkanes from shorter-chain alkanes is old technology. The petroleum industry does that sort of thing all the time to product plastics etc.
Sure, one can use methane generation just to create a cycle so that CO2 emissions stop rising. But I'm thinking further down the road when nanotech replicators make all manufacture incredibly cheap. At that future point we really could afford to build massive artificial photosynthesis systems just to pull CO2 out of the atmosphere. Of course, there are other ways to do this. For example, we could submerge trees on a massive scale.
Suppose CO2 emissions really are a big problem. If nanotech replicators are going to happen within, say, 30 years it probably doesn't make sense to put a lot of effort into cutting CO2 emissions now since we could very cheaply remove the CO2 later.
Imagine what we can do with this technology when we colonize Mars.
Radical environmentalism and climate change fundamentalism are like eugenics was 100 years ago. Eugenics was based on the latest scientific data. It was accepted by almost all respected academics and educated laymen. Laws were passed based on it in the US and around the world. Court decisions were based on it. Only when taken to its logical conclusion by Adolph Hitler, did the fallacy of it become obvious. Let us hope that no modern politician is willing to kill so many people to save the environment.
I'm always surprised that there are still intelligent people thinking that CO2 causes global warming... I thought that this meme went out of fashion about a year ago when they did the correlation study between Cosmic Rays, cloud formation and global temperature.
Funny how some memes just take forever to die...
I've just made up my mind to ridicule any posts that attribute increase in global temperatures to CO2 levels.
Seems that a persistent meme like AGW will only die with ridicule for those scientifically challenged.
I also encourage other "sceptics"/"heretics" (my goodness, the word itself is offensive to me) to do likewise. Nothing too directly offensive as that sort of attack will only trigger a defensive response. But just enough of a nudge to sow a seed of doubt.
The weather will take care of the rest in due time but we don't want the AuGWers to any serious damage in the meanwhile.
1) Ridicule is rarely productive and more often just causes a hardening of positions.
2) Arrogance that you know the answer is unwarranted in this instance unless you happen to be a Ph.D. atmospheric chemist or physicist who has done the math and reads all the peer-reviewed research in detail.
3) Claims that an idea has been discredited fall flat when large numbers of people - including large numbers of scientists actually working in the field in question - believe the idea that you think has been discredited.
I did consult a dictionary. I even consulted a better dictionary. While the word is often associated with intent, it does not necessarily say anything about intent, and it does not necessarily convey any moral judgment. The same is true for any other word I might have chosen.
What you wrote is misleading. That doesn't mean you intended to mislead.
What you wrote is not entirely fair. That doesn't mean you intended to harm anyone.
What you wrote is not entirely balanced or unbiased. That doesn't mean you intended to slant things.
Carbon-neutral is not a carbon sink. And this particular technology doesn't remove anything. Something else would either have to remove the CO2 for the reactor or something else would have to capture the methane produced.
Again, I apologize for offending you. I did not intend to say anything offensive.
I wouldn't get lost in whether this is the 'next big thing' with respect to energy. Even if it were to turn out that way, it is far off yet.
But this is really cool chemistry and physics. I can imagine tweaking the catalysts to produce precursors for polymers and all sorts of stuff. The chemistry that this suggests is plenty interesting all by itself. The right combinations of feedstocks and catalysts could make atmospheric CO2 a potential natural resource... but even as a laboratory curiosity, it is cool.