Catalytic Carbon Extraction in Fuel Cell Production?

garyebickford asks: "I've been following the discussions in the media regarding fuel cells & hydrogen fuel. I have an idea (really a set of ideas) for handling the CO2 issues, which could make fuel cells a better solution. Perhaps someone who know about such things can tell me whether it's workable or not. Speculating wildly, if the carbon could be retained in the process (in a discharge tank, for instance), then it might even be useful as a feedstock for plastics, for example. How might a fuel cell process (both production and use), possibly multistage or incorporating a catalytic pre-process, emit carbon in non-gaseous form? What about a fuel cell that just converted ethanol or higher weight hydrocarbons to methanol, or perhaps a nitrite or another byproduct? Consumers could then recycle this waste to the fuel station at the next fill-up. Even this incomplete process can provide more energy per weight or volume than hydrogen, in theory. Would such a process be possible, or feasible?" "Many fuels can be used in fuel cells, including hydrogen, methane/methanol, ethanol, and ammonia. One of the problems with all these, in fact any system that consumes hydrocarbons (either biomass or petroleum), is that at some point in the process the carbon is released as carbon dioxide. For H2 and NH3 the problem is in the production facility; for hydrocarbon fuels the fuel cell itself emits carbon in some form. Perhaps fuel cell research has tended to think in terms replacing the existing combustion model, with the given that output will be H2O and CO2. Is anyone studying the possibility of fuel cells that have other output chemistry?"

Comments

Doesn't Work - Follow The Energy

[billstewart]

Different molecules have different energy levels in them - you extract energy by combining or splitting them. Different reactions also require a certain amount of energy to make them happen - you can have a reaction that will produce net energy but needs a certain temperature or amount of energy to get it started, and what catalysts do is provide alternate paths for the reaction to happen with less starting energy or lower starting temperatures.

Combining Carbon with Oxygen or Hydrogen with Oxygen produces energy - but splitting up a chain of carbon and hydrogen to get the individual atoms to do that with requires some energy, though it's a lot less than burning the C and H will provide. Catalytic Converters on cars take the unburned hydrocarbons in the exhaust, split them and burn them before they get out the exhaust pipes, and take partially burned carbon monoxide and finish burning it. It's a waste of energy, but it was going to be wasted anyway - the reason to do this is that hydrocarbons and CO lead to air-pollution problems including smog. (They also split various nitrogen oxides to give nitrogen and oxygen; I don't know if this is exothermic or if it's using heat generated by the other reactions.)

You can't split the CO2 up into C and O2 without putting back the energy you got out of that reaction, so a catalytic converter won't help you. You could do things like combine it with calcium oxide to make calcium carbonate, and store that, but the usual way to make calcium oxide is by heating calcium carbonate to get rid of the CO2, so that's really no help.

Re:Why?

[CreateWindowEx]

Also, why bother to do it the hard way when you can just take something like ethanol made from switchgrass, where all the carbon came from the air originally, and then just burn it in a regular engine less than $100 of modification. If you include the additional carbon that is sequestered into the ground by the root systems of the switchgrass (harvesting is basically just mowing off the top), it actually ends up as a net loss of carbon to the atmosphere (or at least enough to compensate for using a 15% addition of petroleum for E85). Yes, ethanol in the US is made inefficiently from corn right now, but converting to a more efficient system is a political problem, not a technological one, and not an insurmountable one. See Khosla's video for more info.

Energy levels

[sf_jeff]

Methane probably has more energy in it than gasoline. It has four high-energy hydrogen bonds while gasoline only has something like 2 per carbon, and the weight of a purely hydrogen and carbon hydrocarbon is pretty close to proportional to the number of carbons. Hydrogen gas has a LOT more energy in it than gasoline per unit mass. They used to power the Space Shuttle booster rockets with it before they switched to solid state fuels (Think plastic explosives). They might not have switched at all, except that they need oxygen to burn it with.

Re:My solution

[parasonic]

Toner sold today is not simple carbon dust. Toner contains carbon but is a plastic with intrinsic electrostatic properties.

Check here for more info.

Brilliant!

[Jtoxification]

This is what is known to the world as Carbon Sequestration, and in fact many very important advances need to be made in this arena. So far, it seems that Germany is leading the world in this area, especially with their development of a carbon-emissions-free coal power plant (by actively capturing carbon in the process.)

While I don't see much good in utilizing hydrogen-carrying fuels over non-carbon-emission methods including hydrogen itself, since one set of methods creates Carbon Dioxide and another set creates water (I hope someone starts an electrolysis debate), you'll still get mad props and points (at least from people like me) if you can get this to work, because I don't see how it could really be problematic especially due to the numerous capture-condusive properties of carbon in its many molecular forms.

This field of research is ripe for harvest, and I'd be willing to bet there are a lot of financial backers willing to invest in working demonstrations.

an answer from a semi-expert

[jstomel]

Alright, so I'm a molecular biologist and I work with a bunch of chemists and biochemists on alternative fules. So, I have some expertise on this, but not enough that I couldn't be understood (think it though). So, here's my understanding. First off, fule cells don't make CO2, that's their big advantage. They convert H2 and O2 into H2O. If they did (and it's possible to design one that does, if you make the hydrogen on the spot from coal, which is one way to avoid running around in a car with a pressurized H2 tank) then it would take energy to pressurize the CO2 for later reclamation. This energy would be taken off of the energy efficency of the car and likely render it less than efficiant. If it used a catylitic process to turn ethanol into ethyl aldahyde and liberated hydrogen (as is possible with enzyme aid, I'm kind of working on that problem), then it would be possible to use the spent ethylaldahyde later to regenerate ethanol for further use. There are two problems: First, this is all equilibrium chemistry. That means that you need a greater concentration of ethanol than ethyl aldahyde to make the reaction proceed forword (for the technical folks, I'm symplifying here, don't complain). That means that if you want the car to use more than half a tank of fuel and you want to seperate the byproduct for reclamition, you need some way to seperate ethyl aldehyde (or whatever) from the ethanol. How the hell do you do that? Current ways of doing this are large, expensive, and energy intensive. It could happen in the future (in theory), but we have no current means. Second, converting the byproduct (ethyl aldehyde) back into ethanol is an energy intensive process. We have no current easy and environmentally friendly means of doing this. One possible future hope (which I would like to develop and exploit in about ten years) would be to bioengineer photosynthetic bacteria to harness sunlight to convert these byproducts back into their fuel product, and then use some purification process (as yet undefined, see above) to reprocess them into stock fuel. Such bacteria does not yet exist, nor (to my knowledge) do the enzymes necessary to make it function. So, in short, yes what you propose is possible. No, it can't be done yet, nor in the next five years. I hope to see such a scheme comming along to market in possibly twenty years, at best. Even then, such a system would only be a very complex and efficient battery for storing the energy of the sun (as all renewable life and fuel is). This would limit the total energy expenditure possible to a maximum of the amount of energy poured on the earth by the sun. We are already dangerously close to using that amount of energy, in twenty years we will likely be using more and all of our various renewable energy schemes will be insufficant. We have only two options, conservation or fusion power (or malthusian disaster, but no one likes that one). I leave it to the rest of you to choose which.