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 »

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 »

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 »

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 »

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 »

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
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
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Chris Bradley »

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 »

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 »

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
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Andrew Seltzman »

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 »

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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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Roberto Ferrari »

Fellows

Dennis is right. Palladium is the solution. Pure H2 and super dry.
Commercial H2 generators use a cell with several Pd tubes (1/8" diam x 4" long). Quantity of tubes depend on the total capacity.
They work with the electrolyte solution at not more than 50°C.
Tracking a manufacturer you can buy the replacement cell for something between 400 / 800 dollars.

Otherwise pick up damaged cells from scrapped generators. Main failure is puncture in one of the tubings so you can eliminate the damaged one, running with the others.

Beware other kind of generators employ a different cell, with a polymer porous to oxygen.

Regards

Roberto
Dennis P Brown wrote:
> 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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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Roberto Ferrari »

Fellows
I will post to the right forum a pdf detailing characteristics of a Pd H2 generator.
Roberto
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Chris Bradley »

For some technical information on palladium as a hydrogen membrane, try the attached.

Approx. 20% alloy of silver nearly doubles the [selective] permeability of pure Pd, plus provides stability against dimensional changes due to phase changes in the process.

A 10% Yttrium alloy has over 3 times the permeability:

(Roberto; you might note that file up to 1 MB can be added directly to the thread. For over 2 MB you need the files forum.)
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Chris Bradley »

Some more info here on the difference between H2 and D2 diffusion.

Interestingly, D2 diffuses ~30% *more rapidly* through Pd than H2, though under 'ordinary diffusion conditions' it selects preferentially for H2...
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Bruce Meagher »

Attached are a couple pictures of a used hydrogen generator I acquired from a wise forum member. I'm hoping it'll be the basis of my deuterium gas supply in the coming months / years. I haven't taken the cell apart yet, but thought some might be interested in the pics.

Bruce
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Dennis P Brown »

Hope you know what the caution is about. Also, if the cell is still viable. Best of luck - remember, dueterium gas like hydrogen can be highly explosive if ignited.
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Roberto Ferrari »

Hi Bruce

Main questions are:
-Is still loaded with electrolyte solution?
Beware because is a sodium hydroxide concentrated solution. (Free of heavy metal ions)
-Is still working the cell?
Is very easily poisoned with the inadecuate water. Follow carefully the manufacturer instructions.
In order to produce deuterium you need to load it with heavy water but before that you need to know if it is operative, so run it in light (deionized) water. Once you confirm operativity, you will need to pour the mixture of water and electrolyte and then reload it with heavy water and fresh electrolyte.
Risks are low. Just leave it generating until rising a pressure, then purge it and generate again in order to purge all air from the cell.
Good luck!
Roberto
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Steven Sesselmann »

These Hydrogen generators used to be quite common in the jewellery trade, they were used to provide a tiny hot flame for soldering. The problem was that the insides corroded away and after a few years the unit was generally a mess.

I chucked out three similar units a few years ago.

Some jewellery tool suppliers might still sell them.

Steven
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https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull »

It must be remembered that tight controls are needed to warrant dry deuterium and nothing else exits the final system. Some here might not appreciate just how tight. All this assumes you wish to obviate the need for professional bottled deuterium, yet, obtain the exact same results in operation.

All these used systems would need to be examined and cleaned and or scrapped and certain parts retained. Sometimes, starting from scratch gives you the tightest controls over the finished product.

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

Post by JohnCuthbert »

Don't forget that, for this to work, the "correct" electrolyte is a solution of sodium deuteroxide. Not seen that on ebay. You could make it from heavy water and sodium. The by product would be deuterium...
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Roberto Ferrari »

John

I think that your assumption would be right if you wish to get ultrapure deuterium but those light hydrogens from a regular sodium hydroxide doesn't seem a problem for the fusor.
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Richard Hull »

It is a matter of how many light hydrogens are in the mix. After all, light hydrogen doesn't fuse in our system.

The tiny amount of ionic carrier needed against the preponderance of D2O in solution will probably not impact the fusion effort,though. It is important to put the smallest amount of sodium into the heavy water that you can. A microflake ought to do it. Just agitate, stir or shake the elecrolyte well to distribute the sodium deuteride in solution.

You only need to support very light currents in the electrolysis process if you are collecting for storage and later use.

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
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Andrew Seltzman »

Using sodium carbonate will prevent any contamination of hydrogen into the deuterium. I used sodium carbonate in my electrolyzer without problems.

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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Roberto Ferrari »

Richard, Andrew

Thanks for your enlighting comments!

Roberto
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Re: Electrolysis of Heavy water - Drying the deuterium gas

Post by Peter Schmelcher »

Deuterium gas generator, dryer, and a mass flow controller.

Richard, I’ve done some preliminary testing of a PEM fuel cell and think it is a reasonable deuterium gas solution provided the heavy water is pure. I am also responding to some other threads rather than duplicating information.

The concept is to generate the deuterium gas on demand as consumed by the fusor using a PEM fuel cell with an adjustable constant current power supply. The constant current supply can be as simple as 2 batteries and a variable resistor. The PEM membrane has some proprietary catalyst coating (platinum palladium carbon etc.) that assists in separating the water molecules into the two different gasses with gas production starting at about 1.4Volts. A new one square inch PEM fuel cell costs about $70. Used science toys start around $15.
http://electrochem.cwru.edu/encycl/art- ... ls-pem.htm

Fuel cell specifications I’ve read suggest a maximum flow rate of 6cc/minute STP at 0.8A. I tested my PEM cell at 1.5A for several hours and then abused the cell for a minute or two at 4.5A (33 sccm). This cell has 0.8 ohm of internal series resistance which generates serious heat at higher currents so the water definitely needs to be circulated and cooled to prevent boiling; however, the activity in the cell looks like a carbonated drink. At 130mA (1 sccm) no additional cooling is needed to remove the 0.1W of heat from the cell.

The water side is the oxygen side and the dry side is either hydrogen, when using regular water, or deuterium with heavy water. The membrane on the deuterium side exhibits some slight condensation so additional drying is needed. Neon John (De Armond) used a refrigeration liquid line dryer for drying room air. Water absorption into the zeolite inside the line dryer is a reversible process with pressure, so you can dry out the dryer using a vacuum.
http://www.neon-john.com/Neon/Shop_equi ... _Index.htm

Another concern is unwanted dissolved gasses in the water potentially diffusing through the membrane; this is mostly CO2 but also O2 and N2. I expect any O2 that diffuses through the membrane will get catalyzed back into water and then removed by the line dryer. Dropping the ambient pressure on the water will reduce the partial pressures of all of the dissolved gasses and this will reduce the contamination percentage by the pressure dropping ratio.

The orifice needs to be sized for a reasonable pressure differential across the PEM membrane at whatever flow rate you are generating. The only purpose of the orifice pressure drop is to protect the PEM membrane from vacuum outgassing or bursting. Somewhere I read that a PEM membrane will withstand a maximum differential pressure of 1Barr before bursting. I limited my testing to a 2 psi differential. For ideas see Chris FAQ – Flow Control:
viewtopic.php?f=6&t=3224#p12734

I mounted the cell vertically in a way that maximizes the height difference between what I decided should be used as in and out water connections. The oxygen bubbles create water circulation into a small storage reservoir that separates out the O2 from the returning water so that no mechanical pump is needed. My storage reservoir is a modified glass syringe. The fuel cell lower water supply connection needs to come out of the fuel cell and go down a couple of inches before connecting to the bottom of the storage reservoir. This prevents bubble surface tension inside the cell from pushing O2 out the bottom connection and stopping the water circulation. The first picture is the cell running at 4.5A, second is condensation on the “dry” hydrogen side. If you look along the upper edges of the cell membrane you can see some excess RTV blocking the movement of the O2 bubbles. Keep in mind that the D2 production rate is twice the O2 rate and that the D2 gas still needs to be tested in a fusor and hopefully a RGA. I also made a 5 second 3.8Meg video of the cell running at 4.5A that I was unable to post.

Peter
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