Something of a Holy Grail among engineers with an interest in a low-carbon future is the idea of replacing fossil fuel gasses with hydrogen. There are various schemes, but they all suffer from the problem that hydrogen is difficult stuff to store or transport. It’s not easily liquefied, and the tiny size of its molecule means that many containment materials that are fine for methane simply won’t hold on to it.
[Isographer] has an idea: to transport the energy not as hydrogen but as metallic aluminium, and generate hydrogen by reaction with aqueous sodium hydroxide. He’s demonstrated it by generating enough hydrogen to make a cup of coffee, as you can see in the video below the break.
It’s obviously very successful, but how does it stack up from a green perspective? The feedstocks are aluminium and sodium hydroxide, and aside from the hydrogen it produces sodium aluminate. Aluminium is produced by electrolysis of molten bauxite and uses vast amounts of energy to produce, but since it is often most economic to do so using hydroelectric power then it can be a zero-carbon store of energy. Sodium hydroxide is also produced by an electrolytic process, this time using brine as the feedstock, so it also has the potential to be produced with low-carbon electricity. Meanwhile the sodium aluminate solution is a cisutic base, but one that readily degrades to inert aluminium oxide and hydroxide in the environment. So while it can’t be guaranteed that the feedstock he’s using is low-carbon, it’s certainly a possibility.
So given scrap aluminium and an assortment of jars it’s possible to make a cup of hot coffee. It’s pretty obvious that this technology won’t be used in the home in this way, but does that make it useless? It’s not difficult to imagine energy being transported over distances as heavy-but-harmless aluminium metal, and we’re already seeing a different chemistry with the same goal being used to power vehicles.
This sounds like a very expensive and complicated form of the carbide lamp. The question is not whether it would work, of course it would, but whether it could ever be economical in comparison to other available methods of energy storage. For example, lithium batteries. I’m really dubious about that.
It would address the “rare element” problem. Kind of like the iron battery.
Yeah, aluminium is notoriously energy intensive to make and reasonably expensive too.
And while the aluminium part might be reasonably safe, the sodium hydroxide is not very nice to biological things (or as I recently found out, flexible rubber buckets – plastic buckets seem OK)
>> aluminium is notoriously energy intensive
There’s also what amounts to the opportunity cost. yes, it *is* totally possible to refine aluminum from bauxite with clean hydropower, in fact, that’s why many aluminum mills are located in places that provide this kind of cheap electricity.
But the thing about hydropower is that, by and large, much of that power was going to be generated anyway because you can’t really stop a river just because nobody is running their air conditioning today.
Given that, there’s probably a better way to use it or at least, a cheaper way to store it, even if you simply decide to skip the aluminum and go right to electrolytic hydrogen.
Also, it should be noted that even though *refining* aluminum from bauxite is all about electricity, and some of that can be pretty clean, actually *mining* the ore and transporting it to the mill is a story about fossil fuels.
>you can’t really stop a river just because nobody is running their air conditioning today.
Yes you can. That’s kinda the point of hydroelectric dams and their reservoirs.
You can certainly impound water for use later, but you can’t really save everything. There are relatively few rivers that can actually be shut off since most rivers big enough for hydropower have other flow considerations, like navigation and fish habitat, and hence have some limited minimum flow which has to go past the dam anyway. (The coolest example is Niagra falls, where during the 60’s so much of the flow used to get diverted tor hydropower that the falls would effectively be shut down at night. Of course, they’d have to turn the falls back on in the morning for the tourists)
Since the river is gonnna flow, you can either just waste the potential energy of the water that you’re going to have to let past the dam or, preferably, find something to do that requires a lot of cheap electricity,
I’m reminded of the famous WW-II story of the raid on the Norsk Hydro heavy water plant . The reason that some obscure company in Norway was was running a heavy-water factory it he first place is that it wasn’t. Hydro was a hydropower company that needed to find a use for their nighttime electricity, so they built a plant to produce electrolytic nitrogen for fertilizer – the heavy water that turned out to be so critical to the war was simply a by-product of the light hydrogen being preferentially consumed, leaving deuterium behind.
The sodium hydroxide is quite dangerous in the short term, it will quickly cause chemical burns, but would fairly quickly get converted to other less dangerous things if released into the environment (reacts with CO2 to form sodium carbonate or bicarbonate, reacts with oils/fats to form soaps, reacts with acids or buffers to form sodium chloride or phosphate or whatever). The aluminium might be less dangerous in the short term, but aluminium is a poisonous element and it won’t ever get converted to something that isn’t. Where do the aluminium waste compounds go after this reaction?. Aluminium has no known function in biology and can cause poisoning:
https://en.wikipedia.org/wiki/Aluminium#Biology
The ‘green’ claim got pretty thoroughly debunked the last time a similar scheme came around these pages: https://hackaday.com/2020/05/26/aluminium-pucks-fuel-hydrogen-trucks/ (yes, the last link in TFA)
How much energy comes out in the form of hydrogen, vs. just heating up the reactants?
Virtually all green energy is some kind of insincere scheme or another. We just need nukes. But you can’t make a bunch of money off that so the problem will never be seriously tackled
Hydroelectric power has its own downsides. Many dams built in the western United States with hydroelectric power in mind are hated vigorously by environmentalists for a myriad of reasons. So low carbon footprint is not the only relevant metric.
That’s all fine and dandy, but what does the coffee TASTE like?
I think the “green perspective” would be not to talk about how realistic it is.
Why not create methane with the hydrogen? Right, because like this, it’ll cost more and create more carbon than just using fossil fuels.
the “green” concept never seems to scale well. Its all warm and fuzzy when a few people are trying it out but take it too the level required for mass consumption it appears to have the same short comings as traditional energy sources. Perhaps the terminology should revert to more sensible term used one time in the not that distant past – “Alternative technology”
Try making aluminium without using carbon based electrodes that are slowly consumed in the process. Drop the carbon hate, it is just showing how little you know.
Even if you get the electricity for “free” (geothermal, hydro, solar, wind) producing aluminum from bauxite generates CO2
https://en.m.wikipedia.org/wiki/Hall–Héroult_process
Sooooo….no this is not a realistic solution to carbon neutral energy transport.
Given enough “green sourced” electricity we can produce the aluminum and sodium hydroxide while remaining carbon neutral.
Ok. Granted.
But if we had an unlimited supply of green energy we could use it any number of ways. We could even use it to suck CO2 out of the air and create new fuel to then be burnt in our old, traditional internal combustion engines. Burning it would re-release the carbon but only what we had previously removed. It would be a carbon neutral cycle.
Yes, removing diffuse CO2 from air and producing fuel would be incredibly inefficient. But I’m not actually plugging this idea. The point is if you start by assuming unlimited clean energy then any process can seem like a viable solution but it doesn’t help in the real world because you actually solved the problem by handwaving, assuming the problem had already been solved.