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trendal
J♠



Registered: 04/17/01
Posts: 20,815
Loc: Ontario, Canada
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What would happen if.... (fuel-cells)
#8621484 - 07/11/08 11:52 AM (15 years, 10 months ago) |
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Take your usual PEM type fuel-cell...and replace the O2 stream going in with a stream of carbon molecules.
Do you get hydrocarbons out of it??
That is, does the hydrogen bond to the carbon molecules in the same way it would oxygen?
Maybe I'm just high...but I can think of at least one thing this would be good for.
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Once, men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them.
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johnm214



Registered: 05/31/07
Posts: 17,582
Loc: Americas
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Re: What would happen if.... (fuel-cells) [Re: trendal]
#8621518 - 07/11/08 12:00 PM (15 years, 10 months ago) |
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Yes its the same type of reaction in theory.
If your actually asking what would really happen, I'm sure shit would jam and the nature of the solid (carbon) would prevent any meaningful reaction from occuring, but in theory its the same if you could design appropriate processes.
If all your asking is if simple reactions like this can be accomplished similar to the water forming fuel cells, then the answer is yes, and it would release energy, just like the water forming version.
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zouden
Neuroscientist



Registered: 11/12/07
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Re: What would happen if.... (fuel-cells) [Re: johnm214]
#8622935 - 07/11/08 06:07 PM (15 years, 10 months ago) |
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Quote:
That is, does the hydrogen bond to the carbon molecules in the same way it would oxygen?
No because the former requires energy, the latter releases it.
H2 + O2 -> H2O + electricity H2 + CO2 -> CH4 + O2 You will definitely need to put electricity in on the left.
With some re-engineering of the fuel cell it might work? Mind you, there are MUCH easier ways to make CH4.
-------------------- I know... that just the smallest part of the world belongs to me You know... I'm not a blind man but truth is the hardest thing to see
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Plasmid
Absent

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Re: What would happen if.... (fuel-cells) [Re: trendal]
#8625576 - 07/12/08 01:48 PM (15 years, 10 months ago) |
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Quote:
trendal said: Take your usual PEM type fuel-cell...and replace the O2 stream going in with a stream of carbon molecules.
Carbon's an element, so it's going to depend what kind of carbon you mean. Graphite perhaps? Maybe an alkyne like acetylene?
Quote:
Do you get hydrocarbons out of it??
As long as it can be reduced, then it should be reduced, so yeah, you'd get hydrocarbons. I don't think it'd be as simple as replacing the O2 stream with (for example) acetylene or ethylene, but yeah, in general it's just carrying out a reduction.
Quote:
That is, does the hydrogen bond to the carbon molecules in the same way it would oxygen?
It's going to depend on a few things: what form of carbon are you starting with? Is carbon going to be the preferred substrate for the reaction or will the hydrogen react with something else?
This should work though. Catalytic hydrogenation of carbon-carbon double bonds can be carried out with H2 and a metal catalyst.
Quote:
...but I can think of at least one thing this would be good for.
Please share . . . unless you want to patent it 
zouden,
Hydrogenation of double bonds would release energy, though. I didn't think that the OP meant to refer to reducing CO2, which yes, would require energy. I guess since he said "carbon molecules" I took this to mean 'molecules made up of carbon only' (which really only brings graphite and diamond to mind - and I don't think you'd try to hydrogenate diamond).
hydrogenation of C-C double or triple bonds is an exothermic process, that is, it releases energy. Alkanes are more stable than alkenes or alkynes, so reducing double bonds with hydrogen releases energy. Check out an organic chemistry textbook for "heats of hydrogenation" which is usually introduced when conjugation is introduced (because benzene and other aromatics don't give off as much energy as non-conjugated double bonds). Cyclohexene gives off about 120 kJ/mol. For hydrogen fuel cells, (1/2)O2 + H2 -> H20 gives about 240 kj/mol. I'm not sure how much energy would be required to convert CO2 to CH4 and 2 H2O.
Edited by Plasmid (07/12/08 02:02 PM)
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johnm214



Registered: 05/31/07
Posts: 17,582
Loc: Americas
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Re: What would happen if.... (fuel-cells) [Re: zouden]
#8625750 - 07/12/08 02:42 PM (15 years, 10 months ago) |
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Quote:
zouden said:
Quote:
That is, does the hydrogen bond to the carbon molecules in the same way it would oxygen?
No because the former requires energy, the latter releases it. H2 + CO2 -> CH4 + O2 You will definitely need to put electricity in on the left.
With some re-engineering of the fuel cell it might work? Mind you, there are MUCH easier ways to make CH4.
He said carbon not carbon dioxide.
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zouden
Neuroscientist



Registered: 11/12/07
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Re: What would happen if.... (fuel-cells) [Re: johnm214]
#8626602 - 07/12/08 06:45 PM (15 years, 10 months ago) |
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Yeah, I assumed carbon dioxide because carbon is a solid and thus cannot be used in a fuel cell.
-------------------- I know... that just the smallest part of the world belongs to me You know... I'm not a blind man but truth is the hardest thing to see
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