Perhaps that analysis was too critical. The analysis assumed was not theoretical maximum efficiency. The news claim was that some "new" catalyst was developed that gets closer to maximum efficiency in the reaction. The reaction involved is 2Al + 3H20 => 3H2 + Al203. Sorry about the illegibility of this. The equation says two moles of aluminum + three moles of water will yield 3 moles of hydrogen gas and a mole of alumina waste compound. Therefore, the maximum yield possible from the equation is: 2 moles of aluminum, with the atomic weight of 27, which gives 54 grams per mole as aluminum input-- and 3 moles of hydrogen gas ( having two atoms of hydrogen in each molecule), which yields 6 grams of hydrogen output. The ratio is then 54/6= 9 grams aluminum per gram of hydrogen. That's the best you can possibly do.
Multiply it by a thousand to get the kilograms. Since it takes 13 kwh to produce 1 kg of aluminum; then it would take 13 kilowatt/hrs times 9 kg per kg hydrogen produced to reconstitute the aluminum from waste. That's too much energy, since it probably would take less energy to just electrolyze water.
Basically, it just doesn't make sense to do this. Even with the best possible yields, it still does not make sense. That's why it will probably be attempted anyway. That's the way society rolls these days. Sadly.
There has been some mention of the possibility of using gallium to extract hydrogen from water. As an energy source, this looks like it could be interesting. So I decided to run some numbers to figure if the thing was feasible or not.
According to one source, it takes a 3 to 1 ratio of gallium to aluminum to make the best composite. The composite will be mixed with water, which produces the hydrogen. It almost seems like magic. The gallium is not consumed, and can be used again and again. Basically, you just have to come up with the aluminum. Ah, there's the catch. Also, what do you do with the alumina mixture? Do you reuse it?
If you were to try to make a "closed loop" of making hydrogen, then reconstituting the aluminum, to be used again, then you won't have an economical set up. That's because of the high energy cost of producing aluminum. Currently, (no pun intended) it uses electrolysis to extract the aluminum from alumina; and it takes 13.2 kwh/kg for the aluminum to be produced. How much hydrogen can thus be produced? The ratio is rather high to extract 1 kg of hydrogen using the gallium/aluminum catalyst.
For each gram of composite used, it makes 130 milliters of hydrogen. But there's 1000 milliters in one liter. What is the ratio in mass? One "mole" of hydrogen masses at 1 gram. Also, 1 mole of hydrogen is 22.4 liters at standard temperature and pressure. Therefore, 130 ml of hydrogen isn't much. The math is 130/22400 grams, where 130 is the amount produced, and 22400 milliters in one mole. One mole of hydrogen masses at 1 gram as mentioned, so this would be .0058 grams. Not much. You would need 1000 / .0058 in order to obtain 1 kg of hydrogen using this process. That would be 172 kg of composite to produce one kg of hydrogen. Divide by three gives the amount of aluminium required--57.3 kg.
The problem is all that energy to get back to pure aluminum. 57.3 times 13.2 kwh/kg for each kg of aluminum by the electroysis process mentioned above. It makes no sense to go this way unless you use scrap aluminum, and you have no intention to recycle the alumina produced to make the hydrogen. It makes much more sense to reuse the aluminum that already exists.
Come to think of it, I may have done all this before. Seems like there was a post on this subject way back when.
Yes, I found that analysis, but it didn't involve gallium. This analysis is no more encouraging that one was. It may make more sense to electrolyze water than to do it this way.
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