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Comment by abirch | Hacker News Reader

If you happen to have an article of converting sea water to methane, please post. My searches bring back methane dissolved in sea water and I'm curious where the carbon originates.

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You're converting Sea water to water (desalination) and then do electrolysis to get H2. You need to get CO2 from somewhere, you can use Direct Air Capture technology to get it from the air. Then you do this: https://en.wikipedia.org/wiki/Sabatier_reaction

This is all known technology, the problem is it's not very efficient. Ultimately the discussion in climate tech circles these days is usually that most people think you'll rarely ever do this. Whenever you can you'll use something more direct, like using Hydrogen directly as an energy carrier.

I love promoting the fact that RF (13.56 MHz) can directly electrolyze saltwater without electrodes (and without desalination). The process was discovered by an amateur radio technician and it was treated like pseudoscience because of breathless local news coverage that made it sound like it was a fuel source.

The YouTube video (“burning saltwater”) is a classic—but there still isn’t a proper study on the efficiency of the process. (The radio technician, John Kanzius, died of cancer).

https://youtu.be/Tf4gOS8aoFk

Edit: here is a scientific paper characterizing the process, which is pretty interesting. No calculation of efficiency, however. https://iopscience.iop.org/article/10.1088/0963-0252/22/1/01...

While he may not have gotten it more widely studied to evaluate the efficiency… did he publish more information about his process? Or did his methodology die with him?

Well, the method is shown in the video. Put a test tube of saltwater in front of an 13.56 MHz RF generator (radio antenna) and light ‘er up.

The paper I posted uses a focused beam of RF and more deliberate lab methodology. But with just 5 citations, I feel like there might be a missed opportunity.

Thanks for posting the paper! With anything RF related it can be a complete shot in the dark for anyone trying to reproduce the work without things like the frequency involved. I mean sure you could do some physics, pick a range of likely frequencies and scan around but then your at the mercy of how much power you can generate at tuneable frequencies and still relying on a bit of guesswork.

Even if it’s not efficient this is a great RF science demo so it’s good to spread the knowledge around. Thanks again for posting it.

It is unlikely that the exact value of the frequency has any importance.

They have used 13.56 MHz just because it is one of the frequencies for which it is easy to find high power industrial generators, which are used e.g. for induction heating.

Here’s a mildly optimistic future vision for large-scale hydrogen production:

* We build arrays of underwater resonating tubes (~ 17 m for 13.58 MHz) that optimize the RF process efficiency for generating hydrogen.

* Out in the open ocean, it’s powered by floating gigawatt solarpads.

* “Blossoms” of enormous mylar cells are continuously filled up with hydrogen.

* The mylar hydrogen cells are plucked and transported for further processing via drone zeppelins.

I like the cut of your jib.

Almost always, people think one new idea is as much as a new technology can take.

But I suspect people will prefer an underwater hose for transporting gases.

That is a fun discovery. But if it's producing the hydrogen and oxygen as a mixture, rather than two separate streams, as conventional electrolysis does, i'm not sure it's very useful.

It’s a good point. Electrolysis produces hydrogen at the cathode and oxygen at the anode, making separation easy. But columnar separation may also be efficient, as the hydrogen will easily float on the heavier oxygen. Not an expert, though.

Stoichiometric mixtures of hydrogen and oxygen are terrifying to work with. No thanks.

So, you separate it while it is still in the water.

How? What's your detailed suggestion for doing this.

"Membranes, my boy. Membranes!"

I just looked it up. Hydrogen is insoluble in water. Oxygen is quite soluble. So, circulating water through, the hydrogen will bubble out, while the oxygen will be carried away with the water. So, maybe no semipermeable membranes needed.

Worth a shot!

If you’re interested, I’d love to put together a technical sketch..

That would be very fun. I was going to email, but couldn't find you at Delft...

J.d.lomas at tudelft dot nl or dereklomas at gm ail

We have good membrane technology now. Lay it on the water surface, so only the H2 gets through.

Does oxygen dissolve more readily in water than does hydrogen? If so, you just keep a continuous flow of water so it doesn't saturate before it moves on, but the hydrogen still bubbles out.

I doubt you want the water hanging about, heating up, anyway.

I just looked it up. Solubility of hydrogen in water is negligible; but oxygen dissolves readily, although better in fresh than in seawater.

i think parent refers to the sabatier process, so the source of carbon is concentrated CO2 externally provided, not from seawater

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