Electrolysis of Heavy water - Drying the deuterium gas

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Richard Hull
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Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull » Fri Jun 22, 2012 2:04 pm

We have had some very few folks obtain their deuterium gas, (very difficult at present to purchase), via electrolysis of heavy water which is rather easy to locate and purchase by comparison.

This process produces far more deuterium gas for the buck than bottled gas, but it is "wet". Their attempts to dry the resultant gas has been less than stellar, but still, servicable in doing fusion.

The tiny moisture remaining after electrolysis can limit fusion due to contamination of the vacuum. Water is the #1 contaminant in any vacuum system, anyway. I am unaware of anyone hitting the million mark with deuterium obtained via electrolysis.

Dry to a person walking around outside is not the same as dry to a vacuum technologist.

If a true, ultra dry, hydrogen electrolysis process could be developed rather simply and cheaply then a lot of deuterium gas acquistion issues might melt away.

Note* there are other issues involved in the mechanics of transporting low pressure deuterium gas, even dry, into a fusor, but getting the gas dry is a big step; perhaps the biggest.

Lets put on the "thinking caps" on this issue. It would certainly help a lot of newbs and others that hit this "deuterium gas wall" in actually doing fusion. (one of two walls...The second is neutron detection). We have had limited discussions on this in the past. If this system and drying issue can be worked out, I will turn the resultant into a FAQ.

Ideas?
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by mitakeet » Fri Jun 22, 2012 2:15 pm

When I have tried to dry things in the past I used chemical drying methods (plain old cotton balls worked fabulous in my organic synthesis days). It would seem ideal in this case since you need such a small amount of gas. Has anyone explored this approach? A more complex method would be to pass the gas over a cold finger (something with dry ice or liquid N2), then across the chemical drier, but for the amounts I figure people need the chemical methods alone should be enough.

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Tyler Christensen » Fri Jun 22, 2012 2:18 pm

I have passed it through a drierite column, which did alright. I also passed it through a copper tube coil that was in a bath of ice water, which seemed to do even better. Ideally, it would be much colder than ice water.

My first neutrons were by electrolysis, although I didn't get very many.

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull » Fri Jun 22, 2012 2:23 pm

I'll start this off. (add on - Wow! you guys were fast! While composing this, what I thought would be the first reply, two posts beat me to the punch.)

Dryerite or other absorbant is OK, but it would also absorb the D2 itself to some degree. I was thinking of a long coiled tube of rather small bore, (tiny volume, large surface area), placed in a styrofoam trough or in a dewar with liquid nitrogen. Even dry ice in alcohol would do. Liquid nitrogen is easy to obtain from most better welding shops and dry ice from most kroeger food stores.

edit: The key issue against ice water is that water would still get through. You need super cold compared to 0 deg. C. Water vapor is not attracted to cold surfaces. It sticks when it contacts it. Sticking is a function of temperature and molecule velocity. Thus, a long time needs to be spent in the tiny, yet long, tortured volume of the coil to warrant a significant "hit and stick" ratio as the water molecules do their "Brownian motion thingy", slowed with every collision that fails to "stick".

Water vapor would stick (freeze) to the walls of the tube, allowing the gas to propagate. The gas could be quarantined in a large container that had been evacuated to atmospheric pressure. It could then be valved off and removed for installation in a fusor's gas line.

The water logged line could now be heated to over 300 degrees C and high pressure argon forced through the line and then valved off, ready for another run.

The concept of freezing out water vapor is not new, of course.

Now.....What should the coil be made of? Most metals absorb hydrogen like crazy. Can you chemists or chem nuts call up an organic tubing that would be better than a coil of metal like copper or SS that would take to the cold and and yet not selectively absorb D2? I worry the advantages of extra D2 for the buck might be lost in saturating the metal tube with H2 before passing on to our capture chamber only to be lost with the subsequent water purge heating. Experiment might be in order here.

It would be great to turn this effort into a fete accompli.

Richard Hull
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull » Fri Jun 22, 2012 4:11 pm

As noted, there are mechanical issues if one gets to trying to mechanize and use this process.

It is important to make sure not even the slightest air bubble remains in the D2 collecting arm. A syringe connected to the arm will assit in warranting this condtion is met.

As the gas collects, you will have to have a petcock above this gas volume. Once the gas collects to fill the collecting arm, you will have to transfer the gas to a heavy vacuum arm that is, itself, valved off. This is to add a safety area in case some liquid water is accidently introduced. (valving to a deep vacuum will be a delicate affair.)

From this safety chamber which might still be at some lower pressure, you can admit the gas to the dryer assembly.

The end of the dryer assembly should attach to a large, deeply evacuated vessel that has yet another leak valve. It will be important to slowly leak the gas into this vessel from the safety vessel through the dryer. You want to slowly transfer the gas as the molecules do not need to rush through the "cold coil". A good thermo couple vacuum gauge on the large final reservoir would be desirable so that you could estimate your gas volume collected.

Standard, simple calculations can be made as to how much gas at STP can be expected via electrolysis. With careful controls, in experiment, one might have to do several fills of the large end reservoir and using its final pressure calculate the efficiency of the process and how much D2 is lost to absorption.

I would imagine a slower electrolysis, (lower current), might be better as heating the electrolyte would not be desirable and keeping the electrolyte in the gas collecting arm in an ice water bath might be nice to avoid a lot of water vapor due to warm solution evaporation from collecting in the gas arm of the electrolyzer.

The mechanics will be interesting and fine tuning it will be another issue.

Richard Hull
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Chris Bradley » Fri Jun 22, 2012 4:31 pm

Could there be any mileage looking into polymer films as a filter (per those used in proton-exchange membranes (PEM) for fuel cells)?

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Andrew Seltzman » Fri Jun 22, 2012 5:25 pm

Phosphorus pentoxide (P2O5) will absorb water exceptionally well.

Using a cooling method, perhaps drawing the deuterium through a tube filled with fine copper wool(larger surface area) would work.

You can also get small amounts of palladium which you might be able to roll into a foil and heat to let deuterium through

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull » Fri Jun 22, 2012 6:12 pm

The molecular seive idea is also exciting. The water molecule (mickey mouse head) is 2.8 anstroms. I wonder what a chunk o' such a seive would run, dollar wise. If the sieve was virtually proof against water passage, that would be the one stop shopping solution.

The copper wool idea is nice provided we would not lose too much D2 into the surface metal lattice.

I found this past posting in a search. Folded in here to collect old posts

viewtopic.php?f=6&t=2654#p12164

Good discussion here too but palladium is still the best leak and is very expensive. But if we collected the gas rather than attempt inline, direct usage at 10 microns constant required drain then this might be more doable with nickel. All good ideas that are now 6 years old.

Who is going to be the first mega neutron fusioneer using heavy water?

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Andrew Seltzman » Fri Jun 22, 2012 8:27 pm

I also remember that Craig Wallace used a heated magnesium column to react with any residual oxygen and water in his deuterium stream. I suppose any reactive metal such as lithium would work at room temperature. You can salvage thin lithium foil from lithium batteries, that might have enough surface area to work well.

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Dennis P Brown » Fri Jun 22, 2012 8:52 pm

Commercial purifiers use a palladium foil and both pressure and temperature on one side to drive it across; out comes 99.9995 purity. A pain to make since stainless steel tubing/fittings would be needed but simple compared to some of the things people build here. If I remember correctly, the temp is three hundred centigrade or so – of course, any air leaks would be ill advised.

The liquid nitrogen approch seems easist and would work very well. A short coil of SS in LN2 should really dry out the gas.

Forgot to add - teflon tubing will not react with deuterium and can be used in LN2.

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