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The carbon dioxide we're currently dumping into the atmosphere started out as atmospheric carbon dioxide hundreds of millions of years ago. It took lots of plants and millions of years of geological activity to convert it to fossil fuels. One obvious way of dealing with our atmospheric carbon is to shorten that cycle, finding a way to quickly convert carbon dioxide into a usable fuel.
Unfortunately, carbon dioxide is a very stable molecule, so it takes a lot of energy to split it. Most reactions that do so end up producing carbon monoxide, which is more reactive and a useful starting material, but it's far from a fuel. Now, though, researchers have discovered a catalyst that, with a little help from light, can take CO2 and make methane, the primary fuel in natural gas. While the reaction is slow and inefficient, there are a number of ways it could be optimized.
The work started out with a catalyst that converts carbon dioxide to carbon monoxide when supplied with a source of electrons. The catalyst is a complex ring of carbon-based molecules that latch on to an iron atom at the center. The iron interacts with carbon dioxide, allowing hydrogen atoms from water to break one of the carbon-oxygen bonds, liberating water. The iron loses some electrons in the process, and these have to be re-supplied for the cycle to start again. Typically, that supply comes in the form of a separate chemical that readily gives up some electrons.
(Score: 4, Insightful) by kaszz on Thursday July 20 2017, @02:47PM (6 children)
Or we can make fuel using dirt cheap sunlight and reduce CO2 at the same time.
One worry is however that the catalyst may be destroyed by the heat.
(Score: 2) by JoeMerchant on Thursday July 20 2017, @04:46PM
Heat, schmeat - run the process in the arctic.
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(Score: 2) by HiThere on Thursday July 20 2017, @05:35PM (4 children)
This wouldn't be useful in reducing CO2, but it might well minimize adding more. It would allow the current CO2 to be used as a fuel, which when burned would return to the atmosphere. Presumably there are inherent inefficiencies in the cycle, and it would need to be powered (by solar cells?).
OTOH, I much prefer solutions which produce a liquid fuel, like oil. There are lots of projects working on making that more efficient. Again, this is just a way of not making things worse, but that is also advantageous. The only way to actually reduce the CO2 is to bury it somewhere. Durable paper lasts pretty well, so support you local library...and insist they hold onto books. Other choices are wood frame houses (can last for centuries, but not as durable as good paper...unless they're made out a treated wood).
The problem is all this small stuff will probably be overwhelmed by methane emissions from melting permafrost...though that's not yet certain. (I.e., we aren't really sure how much methane is locked up down there. It could be enough to power a 4 degree raise just by itself, or it could have mainly drained off earlier.)
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(Score: 2) by bob_super on Thursday July 20 2017, @05:56PM (1 child)
> I much prefer solutions which produce a liquid fuel, like oil
If you generate electricity to feed the CO2 -> CH4 process, you might be able to generate a bit more and run a compressor.
The total ecological benefit of the process depends on raising efficiency of the reaction, to account for the cost of building panels and infrastructure.
(Score: 2) by JoeMerchant on Thursday July 20 2017, @08:12PM
Back to the arctic (and antarctic in the end-begin of year months), run the process all through the midnight-sun to suck down CO2 and convert it into methane, store the methane deep under the sea ice as methyl-hydrates, it will stay locked up there as long as the ice pack never thaws - and since we're solving the AGW problem, that will never happen, right? What could possibly go wrong?
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(Score: 2) by kaszz on Friday July 21 2017, @05:26AM (1 child)
Solar cells are likely to suck for these kinds of applications. The economical ones are at circa 16% efficiency and then you got to add MPPT and DC/AC conversion boxes. High efficiency is at ~43% but they make little economic sense. The better approach is to focus enough sun radiation to cook the CO2 at circa ~2500 ⁰C. This will split the C from the O2. To make CH4 one needs to grab a H4 somewhere.
A burnable gas can be made into liquid through liquification processes. They seem to do it by lengthening the chemical bonds. Which of course consumes energy, no free lunch..
To store carbon, maybe it's better to just keep the C like it is. Other compounds can maybe be used to bind it. But then coal etc all seem to work out just fine. Dig it down under a layer of clay and it will not circulate for quite a while.
(Score: 2) by HiThere on Friday July 21 2017, @04:54PM
1) Sorry, my (GP) reply was almost a joke.
2) For this application you wouldn't need any inverter, just design it to run on DC.
3) This had better a low voltage, low current requirement, or the entire process is worse than just stupid. Even if it is, I'd expect auxiliary costs to swamp any benefit.
FWIW, I expect that plants of some sort (I'm including microbes within plants as long as the convert CO2 to carbohydrates) would, or could be engineered to, do the job both better and cheaper. Except in special circumstances, such as, perhaps, on board a nuclear sub.
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