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Author Topic: Sea water to H2 +O2... How is it done?  (Read 12999 times)

Offline Titanscape

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Sea water to H2 +O2... How is it done?
« on: 29/04/2004 19:23:26 »
Provided I have a current of electricity, how can I turn sea water into it's basic constituents of Hydrogen and Oxygen. keeping if it is a by-product the metals and other gases? Where do they collect if I have the right containers?

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Offline MayoFlyFarmer

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Re: Sea water to H2 +O2... How is it done?
« Reply #1 on: 30/04/2004 00:02:11 »
I can't remember exactly how to turn water into its elements, but the first step would be purifying the sea water.  this is done by reverse osmosis.  Applying a pressure to water to force it through a semi-permiable membrane against the osmotic gradient (very similar to the way dialisis works).  I'm sure canabinoid can tell you how to break the water down.

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Offline chris

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Re: Sea water to H2 +O2... How is it done?
« Reply #2 on: 30/04/2004 02:23:31 »
Sea water is a mixture of ions in solution. You can electrolyse the water using, for instance, 2 carbon electrodes. As sea water is about 3.5% sodium chloride (NaCl) the pairs of chloride ions (Cl-) will migrate to the anode, donate an electron each (which is why current flows through the cell), bond colvalently to form Cl2 and escape as a gas. Hydrogen will be given off at the negative electrode (cathode). The metal ions will similarly migrate to the cathode but you won't make any metallic sodium ! On an industrial scale dried sea water is electrolysed in the molten state and the sodium is collected using a mercury cathode. The sodium mercury amalgam is then reacted with water to produce sodium hydroxide.

Perhaps Cannabinoid could clarify what happens to oxygen in the aqueous electrolysis of sodium chloride ? Presumably the chloride ions are consumed first ?

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« Last Edit: 30/04/2004 02:24:41 by chris »
 

Offline cuso4

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Re: Sea water to H2 +O2... How is it done?
« Reply #3 on: 30/04/2004 08:43:31 »
Both Cl- and O2- are anions, would they react together to form other compounds? Like ClO-?
Or would Cl2 and O2 produced react with the anode? For example in the electrolysis of Al2O3, the oxygen produced at anode react with the carbon electrode to form CO2.

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Offline Ylide

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Re: Sea water to H2 +O2... How is it done?
« Reply #4 on: 30/04/2004 16:21:19 »
If the chlorine reaction has a higher action potential, it will form before the oxygen starts, (they're both at the anode) and I'm pretty sure that's the case.  I know it happens at much lower voltages, as you can do it with a 9V battery, but water itself takes a LOT more energy.

Even though the chlorine gas comes out sooner, they could still react in whatever container you have above the anode to collect the gas, as angel suggested.  If you want separate oxygen, you'd need to use a lower voltage to drive off the chlorine and then change containers at the anode and ramp up the voltage to a level that will electrolyse water.



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Offline Hydrometer

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Re: Sea water to H2 +O2... How is it done?
« Reply #5 on: 24/07/2004 06:51:02 »
Actually, electrolyzing seawater just to obtain Hydrogen is quite simple to achieve. Using any inert electrodes would do the job. However, the real issue should be focussed on the by product Chlorine (a toxic gas with high solubility in water) that should be suppressed from being evolved. The only way to achieve this is by promoting oxygen evolution at the anode instead of the Chlorine evolving anodic reaction. Although in theory, any electrolysis of alkaline solution employing inert electrodes such as carbon should yield both Hydrogen and oxygen, but this not so in real life practice. One simple approach to this problem is by employing electrode materials (anode materials) which shows high selectivity for oxygen evolution even at extremely high salinity seawater.

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Offline chris

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Re: Sea water to H2 +O2... How is it done?
« Reply #6 on: 30/07/2004 06:08:22 »
I did not realise that the electrode material could affect the species of gas evolved from the anode. How is that achieved ?

Chris

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Offline feathertripper

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Re: Sea water to H2 +O2... How is it done?
« Reply #7 on: 22/11/2004 20:48:49 »
Let me take a stab at this.

Seawater is NaCl and H2O.  (Salt water)

If you had just fresh water, plain H2O the Chlorine wouldn't be a problem.

I don't really know if this is right so someone correct me if I'm wrong.  Cl and O are both - (negative) and so therefore would both be attracted to the anode (positive) electrode in electrolysis.  I think the problem with the whole thing is that the chlorine is more highly reactive than the oxygen.  (Something to do with being a halogen?)

I don't know if Chlorine production is technically a 'problem' though, Chlorine has a bizillion commercial and industrial applications.  Why not put it to use?
 

Offline feathertripper

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Re: Sea water to H2 +O2... How is it done?
« Reply #8 on: 06/12/2004 17:23:05 »
Ok so... Let's sum up

Chlorine, being more reactive than the oxygen, will seperate itself out with the Hydrogen at lower voltages, leaving you with Sodium Hydroxide, most likely.

Getting the Chlorine out first is pretty much what you have to do.
Um... And Chlorine is a toxic gas in pure form, so uh... do this somewhere with good ventilation :D

As for actual equipment, I know they make little contraptions for getting H2 and O2 from regular H2O, but with the Chlorine taken into account you'll prolly have to get a little creative on your own.

Anyone got any tips on that?

(Yay for playing with toxic gases!)
« Last Edit: 06/12/2004 17:30:24 by feathertripper »
 

Offline chiralSPO

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Re: Sea water to H2 +O2... How is it done?
« Reply #9 on: 17/08/2013 16:28:10 »
Depending on the pH of the solution and the material the anode is made of, oxidation of Cl to OCl or Cl2 is typically the major reaction at the anode. However, there are catalysts that can be deposited on the surface of the anode that can selectively oxidize water to oxygen, even in the presence of high concentrations of Cl. So it is possible to split seawater into hydrogen and oxygen, but it is more complex than a simple electrolysis.
 

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Re: Sea water to H2 +O2... How is it done?
« Reply #9 on: 17/08/2013 16:28:10 »

 

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