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Reply #7: More simply, methane (CH4) can be thermally decomposed to form carbon and H2 ... [View All]

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eppur_se_muova Donating Member (1000+ posts) Send PM | Profile | Ignore Tue Aug-16-11 04:41 PM
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7. More simply, methane (CH4) can be thermally decomposed to form carbon and H2 ...
Edited on Tue Aug-16-11 04:50 PM by eppur_se_muova
this is how high-purity graphite is produced. The question is whether the combustion of H2 can generate enough energy to balance the energy cost of CH4 decomposition. Since you are not burning the carbon, you are recovering only part of the energy available from the fuel. This would mean *more* hydrocarbon would have to be burned to provide the same amount of energy. Now, there are other possilities, but they all face another issue -- what are you going to do with all that leftover carbon? Only a small fraction of petroleum is used to make plastics and intermediate chemicals; the rest is burned for fuel. The raw materials needed for production of plastics etc. is much smaller than the amount needed for fuels. So even if you succeed in "partial combustion" of HC's to form carbon and H2O, you're going to do it at the cost of pumping *more* oil out of the ground, and having to find a use for all that carbon you've brought to the surface -- and whatever you do, don't let it catch fire!

In regard to your question, "has anybody here really looked at this" (or something similar), I think you can safely say that yes, some of us have thought about this. Basically, it doesn't do enough to shift usage away from fossil fuels, since it all depends on propene. If you're going to use biomass to generate the propene, then partial combustion is kind of unnecessary, since you've closed the loop in the carbon cycle.

on edit: hadn't read your reply to a reply to the OP when I wrote this:

PS: PAN can be thermally decomposed to form carbon fiber and NH3 -- which potentially can be recycled to make more acrylonitrile, and thus more carbon fiber. So the overall process is propene + O2 --> carbon fiber + H2O. Pretty neat, assuming high efficiency at each step, which probably doesn't happen, or else carbon fiber would be a bit cheaper.
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