Methane from Carbon Dioxide and Hydrogen


by petweis
Tags: carbon, dioxide, hydrogen, methane
petweis
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#1
Mar26-08, 02:49 PM
P: 3
In the 18th century methane was made from carbon dioxide (from the air) and hydrogen (from water) and used as the fuel for the lights of the "Gaslight" era.

Seems to me, that if we could take carbon dioxide out of the atmosphere, add hydrogen and obtain methane, a very clean burning fuel, we could solve two problems in one fell swoop - reducing the carbon in our atmosphere, and obtaining an almost inexhaustible source of energy.

I realize that the carbon is returned to the atmosphere, but since buring methane yields far more energy than burning coal, oil or gasoline, and burns much, much cleaner, (carbon and water are the only burning products), using methane to generate energy, (as in powerplants and for transportation) would result in a much reduced carbon load into our atmosphere for the same amount of generated energy, as compared to coal, oil and gasoline, and their many dirty byproducts (smog).

I just don't know how much energy it takes to produce methane from atmospheric carbon dioxide and hydrogen, and how this compares to the production costs, and carbon footprint, of coal, oil and gasoline. If it can be done with bacteria, which exist, I would think that the production costs and carbon footprint would be extremely low.

It would take a Chemist though, which I am patently not, to work out all the details.

Any elucidation would be much appreciated.

Cheers;
petweis
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JGK
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#2
Mar26-08, 03:14 PM
P: 21
I think your on the wrong track on this one. This Link gives the equation for methane combustion as:

CH4[g] + 2 O2[g] -> CO2[g] + 2 H2O[g] + energy

all you're doing is cycling the CO2
chemisttree
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#3
Mar26-08, 03:28 PM
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To go from carbon dioxide and hydrogen to methane presupposes that you have a large source of hydrogen, which is of course the cleanest burning fuel of all. I use the term 'fuel' for hydrogen in the narrowest of ways since it really isn't a fuel at all but is an energy storing material as is any methane generated by it and CO2. If you had a carbon-neutral source of hydrogen at your disposal, it would be much more efficient to use it as a fuel rather than go through the effort to convert it to methane. Methane is much more suitable for ease of use and distribution but it is generally not so good for smog elimination or for use as a transportation fuel since it doesn't have the energy density.

Chemically-speaking, you must add the energy to produce hydrogen to the energy needed to produce methane from CO2 and H2 to get the true energy balance. You will find that the burning of methane is isoenergetic with it's production from CO2 and H2 and so it isn't a fuel at all. It is a storage medium for energy in this context.

Moonbear
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Mar26-08, 03:51 PM
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Methane from Carbon Dioxide and Hydrogen


Quote Quote by petweis View Post
In the 18th century methane was made from carbon dioxide (from the air) and hydrogen (from water) and used as the fuel for the lights of the "Gaslight" era.
As far as I know, natural gas was used (i.e., methane from coal deposits and sewer systems) and possibly the side products of coal burning. The Sabatier process was not invented/discovered (whichever you want to call it) until the late 19th/early 20th century. http://en.wikipedia.org/wiki/Paul_Sa..._%28chemist%29

Seems to me, that if we could take carbon dioxide out of the atmosphere, add hydrogen and obtain methane, a very clean burning fuel, we could solve two problems in one fell swoop - reducing the carbon in our atmosphere, and obtaining an almost inexhaustible source of energy.
As JGK pointed out, assuming a completely efficient process (which is never practically achieved), you'd have a net energy output of 0 after accounting for the energy put into the production of the methane. Your idea of an inexhaustible energy source violates the laws of thermodynamics.
petweis
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#5
Mar26-08, 06:14 PM
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To JGK and all;

"all you're doing is cycling the CO2"

If all we're doing is cycling the CO2 out of, and back into the atmosphere, that would be wonderful. We woud have a carbon neutral source of fuel - instead of taking carbon out of the ground and adding to our atmosphere as in the combustion of coal, oil and gasoline.

methinks it's worth exploring the possibilities.

Now it all depends upon how much carbon is added to our atmosphere in the production of methane from atmospheric carbon and hydrogen. But I would wager that the carbon footprint of mining coal, drilling for oil and making gasoline is huge. I know, for example, that the production of oil from tar sands entails a huge carbon footprint.

And I am well aware of the laws of thermodynamics. I meant inexhaustible - not perpetual - in the sense that for our intents and purposes here on Earth, sunlight and tidal power are inexhaustible sources of energy - until the hydrogen fuel of our sun is exhausted and the sun undergoes a phase shift to a red giant.

And I agree that hydrogen fuel is the cleanest and most efficient fuel. But the chemistry of hydrogen fuel is well in hand, and can only get better and more efficient. This is not my concern.

My concern is to find a cleaner source of energy than coal, oil and gasoline.

I am also well aware that methane can be and is being produced by fermentation of manures in 'digesters' by bacteria. But if all the manures of the US were converted to methane, it would only amount to 1% of the annual energy consumption of the US.

with many thanks for all your comments.
petweis
russ_watters
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#6
Mar26-08, 06:28 PM
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I don't think you do understand the thermodynamics or the chemistry, though it was explained quite well already. The point is that there is no energy generated by the process you describe. So it changes nothing about our current energy or environmental issues. We still need all the regular electric power plants we have now plus more plants to do what you suggest. So it accomplishes nothing whatsoever.

What you suggest is not a source of energy, it is an energy carrier, akin to a rechargeable battery.
JGK
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#7
Mar27-08, 06:46 AM
P: 21
Plus given the stats that "industrial processes" account for say only 5% of the atmospheric carbon load. Wouldn't it be better focussing our attention to dealing with the 95% side of the equation?
russ_watters
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#8
Mar27-08, 05:03 PM
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The way I would put it is that the first thing that needs to be addressed about our hydrocarbon energy situation is the coal plants that currently produce half of our electric power. There is a simple solution to them: nuclear power.
petweis
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#9
Mar27-08, 07:33 PM
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That's what I am trying to do; come up with an idea to replace coal, oil and gasoline as power sources - which contribute about 95% of the carbon load of our atmosphere.

And please; do note that I fully understand the laws of thermodynamics. I am not proposing a perpetual motion type of energy source, and I am fully aware that the making of methane from carbon dioxide and hydrogen requires energy, and that the energy output will be less than the energy input.

Here is the model: From "Mars Direct" - NASA'S proposal for a manned Mars Mission:

"The plan involves launching an unmanned Earth Return Vehicle (ERV) directly from Earth's surface to Mars using a heavy-lift booster (no bigger than the Saturn V used for the Apollo missions), containing a supply of hydrogen, a chemical plant and a small nuclear reactor.

The ERV would take some eight months to reach Mars. Once there, a relatively simple set of chemical reactions (the Sabatier reaction coupled with electrolysis) would combine a small amount of hydrogen carried by the ERV with the carbon dioxide of the Martian atmosphere to create up to 112 tonnes of methane and oxygen propellants, 96 tonnes of which would be needed to return the ERV to Earth at the end of the mission. This process would take approximately ten months to complete."

If it works on Mars, we know already that it works much better here on the Earth. And it seems to me that recycling the carbon already in the atmosphere, and using it to make methane, a transportable storage medium for energy, would be a carbon neutral means of providing power for transportation and powerstations.

The bottom line is that this would not take carbon out of the ground and add it to our atmosphere. The carbon is in the atmosphere already, and it can be readily combined with hydrogen, to yield methane, an energy storage medium, if you will. We would just be cycling the carbon out of and back into the atmosphere - and very little new carbon would be added to the atmosphere in its production; far, far less than that added to our atmosphere by the production, processing and transport of coal, oil and gasiline.

And compared to coal, oil and gasoline, it would be a much cleaner medium of energy, not only in combustion - but also in production.

Unlike oil and gasoline, this method would not require geological exploration, exploratory drilling, drilling, pipelines and their pumping stations, and transport to end user - all substantial producers of carbon dioxide, all of which pale compared with the carbon footprint of oil from tar sands.

Let's say that the carbon footprint of the oil and gasoline refineries would equal the methane generating stations - an extremely conservative estimate. The great advantage is that these methane generating stations can be placed everywhere. Every town an city can have its own methane generating stations, wich would eliminate the need of about 90% of the transport expenditures for oil and gasoline. If the "Mars Direct" model is any indication, even large ships could have their own on board methane generating stations.

Altogether, the bottom line is that the carbon footprint for methane would be far less than that of coal, oil and gasoline production and distribution.

And I would never even begin to presume that we can safely store nuclear waste underground for 24.100 years, the half-life of plutonium, or for 4.47 billion years, the half-life of uranium. It would be sheer and utter folly.

with many thanks for all your comments;
peter;



"The plan involves launching an unmanned Earth Return Vehicle (ERV) directly from Earth's surface to Mars using a heavy-lift booster (no bigger than the Saturn V used for the Apollo missions), containing a supply of hydrogen, a chemical plant and a small nuclear reactor.

The ERV would take some eight months to reach Mars. Once there, a relatively simple set of chemical reactions (the Sabatier reaction coupled with electrolysis) would combine a small amount of hydrogen carried by the ERV with the carbon dioxide of the Martian atmosphere to create up to 112 tonnes of methane and oxygen propellants, 96 tonnes of which would be needed to return the ERV to Earth at the end of the mission. This process would take approximately ten months to complete."

We know it works here on Earth
clouded.perception
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#10
Mar27-08, 07:56 PM
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No, no, you're missing the point.

Converting CO2 to methane would take more energy than what you'd get out of burning it (the energy used in CO2 --> methane would be equal to the energy gained in methane --> CO2, plus energy would be lost in the process because no process is 100% energy efficient). So it wouldn't produce any energy at all -- you'd need even more energy from other sources in order to make the fuel.

That's not even counting the process of getting the CO2 out of the atmosphere.

C neutral? Yes. Energy-producing? No.
russ_watters
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#11
Mar27-08, 08:36 PM
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Quote Quote by petweis View Post
That's what I am trying to do; come up with an idea to replace coal, oil and gasoline as power sources - which contribute about 95% of the carbon load of our atmosphere.
I'm not really sure how many times or ways we can say this: your idea cannot replace any power sources because it does not provide a source of power. It only provides a source of power storage.
And please; do note that I fully understand the laws of thermodynamics. I am not proposing a perpetual motion type of energy source, and I am fully aware that the making of methane from carbon dioxide and hydrogen requires energy, and that the energy output will be less than the energy input.
Ok....so if you understand that, why can you not understand that the idea cannot replace any energy generation?
Here is the model: From "Mars Direct" - NASA'S proposal for a manned Mars Mission:

"The plan involves launching an unmanned Earth Return Vehicle (ERV) directly from Earth's surface to Mars using a heavy-lift booster (no bigger than the Saturn V used for the Apollo missions), containing a supply of hydrogen, a chemical plant and a small nuclear reactor. [emphasis added]
The energy comes from a nuclear reactor. So in order to make your idea happen, we'd need to build hundreds more nuclear power plants.....which, of course, could instead be used on their own to replace our coal plants. Don't you see: you don't gain anything by doing this.

Now one day, perhaps, we may need to do something like this to power our cars, but again, there is no fundamental difference between your idea and a battery. Cars powered by methane produced by your process are electric cars ultimately powered by the conventional power plant that generated the energy to make the methane.
And I would never even begin to presume that we can safely store nuclear waste underground for 24.100 years, the half-life of plutonium, or for 4.47 billion years, the half-life of uranium. It would be sheer and utter folly.
It would. It is also a non sequitur: there is no need to safely store nuclear waste for that long. For two reason:
-Virtually all nuclear waste is recyclable and the final products are less harmful than when they were originally dug out of the ground.
-We aren't going to be around long enough to care about storing the waste for 24,000 years, much less 4 billion.

I don't mean to be condescending here, but since the answer has been given to you half a dozen times already, I feel compelled to say it half a dozen times again:

The energy comes from a nuclear reactor.
The energy comes from a nuclear reactor.
The energy comes from a nuclear reactor.
The energy comes from a nuclear reactor.
The energy comes from a nuclear reactor.
The energy comes from a nuclear reactor.
russ_watters
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#12
Mar27-08, 08:38 PM
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We have, of course, glossed over another problem:
Quote Quote by clouded.perception View Post
No, no, you're missing the point.

Converting CO2 to methane would take more energy than what you'd get out of burning it (the energy used in CO2 --> methane would be equal to the energy gained in methane --> CO2, plus energy would be lost in the process because no process is 100% energy efficient). So it wouldn't produce any energy at all -- you'd need even more energy from other sources in order to make the fuel.

That's not even counting the process of getting the CO2 out of the atmosphere.

C neutral? Yes. Energy-producing? No.
Yes, no process is ever 100% efficient, so yes, this process would waste energy compared with a regular power plant - and probably also compared with a battery (batteries are very efficient).

But I figured we'd work on the first law of thermodynamics before moving on to the second...
JGK
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#13
Mar28-08, 07:16 AM
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Quote Quote by petweis View Post
That's what I am trying to do; come up with an idea to replace coal, oil and gasoline as power sources - which contribute about 95% of the carbon load of our atmosphere.
That wasn't what I said, you are posing the scenario to replace coal, oil and gasoline as power sources which only form part of the 5% carbon load from "industrial processess" and not 95% as you claim.

Also, the extrction of CO2, from whichever source to produce the methane may require more energy input than generated by the methane combustion. This would end up increasing the propotion of the carbon load produced by industry (man)


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