Clean energy claim: Aluminum in your car tank

[soylent]

2Al + 3H2O --> 3H2 + Al2O3 + heat

Isn't it 2Al + 6H2O --> 3H2 + 2 Al(OH)3 ?

The difference would not be negligible, aluminium hydrate would suck down an extra water molecule per H2 and it requires some extra energy to get rid of the water when you heat it during the electrolysis(2 Al(OH)3 -> 3 H2O + AL2O3).

Seriously though check this out. Maybe it deserves a new thread. Hydrogen from starch.
http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000456

Evolution has sure turned up some really exciting mechanisms to accomplish at neutral PH and body temperature the kinds of things we can only do at extremes of temperature, pH, presure and with toxic inorganic chemicals. Some of the most curious examples are oil eating soil bacteria, nitroglycerin degrading bacteria and some kind of fungus growing near Chernobyl that appears to be deriving energy from ionizing EM radiation and grows better in the lab under irradiation with gamma rays.

 

[RussSchultz]

Isn't it 2Al + 6H2O --> 3H2 + 2 Al(OH)3 ?

The difference would not be negligible, aluminium hydrate would suck down an extra water molecule per H2 and it requires some extra energy to get rid of the water when you heat it during the electrolysis(2 Al(OH)3 -> 3 H2O + AL2O3).

If it is, don't blame me. I copied it from the Purdue presentation.

 

[Sxotty]

The thing I linked uses natural pathways that don't occur together in nature though. Still nature is responsible for catalyst just not those together b/c they don't produce the most energy for organisms.

 

[soylent]

The thing I linked uses natural pathways that don't occur together in nature though. Still nature is responsible for catalyst just not those together b/c they don't produce the most energy for organisms.

Nature did all the heavy lifting and would easily stumble onto combining those enzymes that way if it was beneficial.

 

[Mintmaster]

It just separates the H2 from the O2, but the O isn't free, so you need oxygen injected into the system. Also, eventually the aluminum will completely oxidize and the process can't continue.

Actually, looking at the equation, it seems like you would need new aluminum pellets for each 'tank' of water. If a tank of water only gets you 300 miles, then it's got a long way to go before its viable.

I think _xxx_ was referring to the use of H2O from the combustion back into the hydrogen creation. It's kind of neat, with the water creating hydrogen which is burned to create water. Depending on how good your water recovery at the exhaust is, you don't need much water stored.

It's a pretty neat idea that drastically improves energy density, but efficiency is the part that sucks. Regenerating the Al isn't great, and it'll be hard to harness the non-H2 half of the energy released when generating the H2.

That seems to be true for nearly all implementations of an H2 economy. What really sucks is the way electricity is generated in the US. Until we get some kind of drastic turnaround here (50+ years?), H2 is only going to be worse for the environment overall.

 

[RussSchultz]

No, for each molecule of water, you get one molecule of H2. The O goes and bonds with the aluminum.

You have to inject O2 into the system to get combustion, that gives you more water which you can crack apart, but you don't have a 'closed' system.

 

[Frank]

So, how much energy would it take to generate one tank full of aluminium and gallium, and how much could you extract from that? Aluminium needs a whopping amount of electricity to separate it from oxygen if I'm not mistaken.

 

[Mintmaster]

No, for each molecule of water, you get one molecule of H2. The O goes and bonds with the aluminum.

You have to inject O2 into the system to get combustion, that gives you more water which you can crack apart, but you don't have a 'closed' system.

Did I ever say otherwise? Of course it's not a closed system.

I'm just saying it's possible to keep feeding the water back in to reduce the amount of weight you carry. It's not really the tank of water that's the fuel. It's a chunk of the alloy.

So, how much energy would it take to generate one tank full of aluminium and gallium, and how much could you extract from that? Aluminium needs a whopping amount of electricity to separate it from oxygen if I'm not mistaken.

The Purdue website above has a presentation with the info. He said this process is about 50% efficient, and only about half the energy is in the form of hydrogen, which loses even more energy in the engine. Hence my concerns about energy efficiency. The guy made a pretty big gaffe there in thinking this could be used with hybrid cars.

The energy cost is about 9kWh per pound of Al generated. At an optimistic cost of $0.02/kWh, it's about the same cost as $3/gallon gas. Not so hot.

In the end, we have an economically feasible way of densely storing energy without hydrocarbons. It's not efficient, but could be useful if that doesn't matter some time in the distant future.