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[*] posted on 13-5-2020 at 22:14
Distallation of Salt


Hi All,

My question is far from a practical question. Just asking to gain more knowledge and see what the general thoughts are on this.

I was reading up on the purification of Salt. Plain old table salt or simply NaCl. Now there is obviously a variety of ways to do this, many of which can be done by an amateur at home.

One thing I did not find anything about. Distillation. As I said, this will be far from practical, with a boiling point of 1465C. That is quite obvious. The equipment needed to safely boil anything at these temperatures, let alone an aggressive salt, will require quite a set-up.

However, is this being done or has it ever been done? Would this give a very high purity of NaCl? Are there any other benefits to it? (Many disadvantages are quite obvious, but sure there are many more I haven't thought of...) And if it is being done, what would be the basic set-up for a kit like this?

Curious to hear what you guys think and/or know about this.

Joey
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[*] posted on 13-5-2020 at 23:15


I would quess that using unconventional methods like thermochemical heating, electric arcs, microwaves (maser or laser) etc would allow for heating up to a plasma.

There are refractories that can withstand temps up to 3800C so in theory distilling stuff up to 2000C should be possible. The reactivity of these materials is another issue, inert gas or high vacuum would do only it's part but contact with the materials may not. Some materials literally dissolve into each other like sugar into water, like carbon does to steel.

Lower BP stuff like mercury, sulfur, etc. are indeed routinely distilled to high purity.

Practical way of purifying NaCl? Nah. It would be orders of magnitude cheaper to chemically recompose it to high purity. Then, many compounds can melt at certain temp, but they'll as likely begin to decompose, although at cooling they probably react to each other in case they are not getting separated. For example, calcium sulfate with silicon dioxide was commercially pyrolyzed into sulfur trioxide and calcium silicate at ~1400C.
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[*] posted on 14-5-2020 at 01:40


as refinery said, it's not impossible to get to the boiling point if NaCl, but if you are trying to purify it that way, it must be inert to the atmosphere and to the apparatus it is being distilled, and finding something that doesn't melt at that temperature and doesn't leach or reacts with sodium chloride at that temperature is really not worth it, fractional crystallization is wayeasier




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[*] posted on 14-5-2020 at 04:27


It is done routinely with ammonium chloride...
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[*] posted on 14-5-2020 at 06:31


Yes, but the boiling point of ammonium chloride is a mere 520 C.



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[*] posted on 14-5-2020 at 17:59


Done a little more searching. Have an idea.

Givens:
- Melting 800C.
- Boiling 1450C.
- Extremely Corrosive.
- Tantalum has a melting point of over 3,000C.
- Tantalum corrosion rate of 0.0005g/m2/day for molten salt. Rate is similar for Br and I but is significantly higher for F. No info on gaseous state of NaCl is available to me.

Finds:
- Electrical Heating Elements 1800C.

Idea:

- Reactor vessel made of Tantalum.
- Inside this vessel is place a double walled vessel made of Tantalum.
- Heating element for boiling is placed inside double walled vessel.
- Top of double walled vessel has a small tantalum pipe to it which sticks out and will allow for vapours to escape to main vessel.
- An additional pipe on the top of the boiling vessel will allow for adding additional salt.
- Due to very large temperature difference between liquid and vapour, these vapours from boiling vessel will condensate inside main vessel.
- Heating element in bottom of main vessel to keep the salt liquid. Actual heating element is placed inside a tantalum tube.
- A small tantalum overflow pipe in the shape of a 'U' will allow for automatic discharge of liquid NaCl with a given volume. Conceptually much like the well know Soxhlet Extractors.
- Refractories, would be on the OUTSIDE of the vessel and not on the inside to avoid contamination.
- Obviously, the entire device is continuously purged very slowly with Argon.

Edit Additions:

- Just in case shit hits the fan a safety measure. A fairly large Tantalum pipe at the top of the main reactor vessel. This should be of sufficient length to allow the pipe temperature to be reasonably low at which point it will go to a cheaper and easier material such as stainless steal. This in turn will go to a SS vessel. All filled with Argon. So even though there is an open connection to this vessel there is no interaction between the main reactor vessel and the emergency dump vessel. When things go wrong it does not really matter anymore, as long as it is contained. Which is exactly what this vessel does.
- Both the main reactor vessel and the boiling vessel will need a dump line on the bottom for emptying the vessel. Maintenance come to mind. Valves is not an option really, so both lines would be closed with a solid salt plug. On the outside of these drain lines there will be a heating element to melt the salt and allow for draining the vessel. This is obviously not good enough for an emergency because of the heating time. But for this we already have the Emergency dump vessel.

End Edit

Result would be a clean, pure salt of which the main contaminant is Tantalum, which by itself is not a very reactive metal, and therefore, as a contaminant does not cause too much trouble.

And yes, this would cost a huge amount of money.

But..

Could the concept work and would it potentially offer something that is not obtainable in other ways.

Joey

[Edited on 15-5-2020 by JoeyJoystick]

[Edited on 15-5-2020 by JoeyJoystick]

[Edited on 15-5-2020 by JoeyJoystick]
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[*] posted on 14-5-2020 at 19:28


That's quite an apparatus you describe.

Hard to actually get your hands on though.

Such a piece of equipment may elude you like an apple that slips out of your grasp when the wind blows raising the branch out of reach.

It could be like standing in a lake, but being unable to drink because the water recedes from you when you bend over to slake your thirst.

Yes, seeking such a piece of equipment may eventually make you feel like you're in the ninth circle of hell.

One question about this distillation: What if the impurities are also volatile at under 1450C ?






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[*] posted on 14-5-2020 at 20:04


Quote: Originally posted by SWIM  


One question about this distillation: What if the impurities are also volatile at under 1450C ?



I am not sure I understand your question correctly.

But let me give it a go anyways. If I am on the wrong track, please rephrase your question.

The salt introduced in the boiling reactor would have to be as clean as possible to start with. But I think that speaks for itself. If anyone was to be crazy enough to attempt this, they would understand that there is no such thing as a short cut.

There is obviously a number of impurities present albeit all in already very low quantities. Some if these will have volatilities that may actually interfere and come out with the NaCl. But I think this is a known issue with distillation. And even though some will come out with the boiling, it will still be significantly less overall and also less for those that do come out with the NaCl.

The only thing added by the distillation apparatus is going to be some Tantalum. This would be in minute quantities and would not be the kind of contaminant that offers the biggest concern because of its inertness to, well almost anything really.
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[*] posted on 14-5-2020 at 20:09


Quote: Originally posted by SWIM  


Hard to actually get your hands on though.



I think the only issue is money. Tantalum is fairly pricy at 500 - 1,000USD/kg. And those are Chinese prices. High quality prices I have not found but would probably be double or more.

Still the price of Tantalum is not the biggest concern. It is the manufacturing of the reactor vessel that is going to be the pricy part. It is not easy to make sheets and tubes. And welding stuff like that together is also challenging.

So yes, hard to get your hands on. But it can be done I think. Just money and time. It will take time to get this build.

Joey
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[*] posted on 14-5-2020 at 20:11


I may have it wrong, but to try and highlight the point.
What if the main contaminant you have in your product is KCl? The BPs are very similar. Would your setup actually separate these?
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[*] posted on 14-5-2020 at 20:11


Tantalum chlorides are probably much more volatile than sodium chloride, unfortunately. This means likely corrosion of the apparatus.



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[*] posted on 14-5-2020 at 20:40


Quote: Originally posted by B(a)P  
I may have it wrong, but to try and highlight the point.
What if the main contaminant you have in your product is KCl? The BPs are very similar. Would your setup actually separate these?


I think you're right. I do not have enough knowledge to determine if you can boil of the KCl before the NaCl. The difference in BP is a mere 45C which is not a lot at those high temperatures. If possible it would still not be very practical.

Take a look at the below specs I found.

https://www.sigmaaldrich.com/life-science/core-bioreagents/b...

It shows a very low K content of between 0.05% - 0.005% It does, however, not say if this is in the form of a chloride or not. I think it is, because how could it be stable in a chloride in the first place. Ok, I am not a chemist, but that's what comes to mind.

The same list also shows a variety of other contaminants. Many of which would see there contents being reduced I think.

Joey

[Edited on 15-5-2020 by JoeyJoystick]
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[*] posted on 14-5-2020 at 20:51


Quote: Originally posted by WGTR  
Tantalum chlorides are probably much more volatile than sodium chloride, unfortunately. This means likely corrosion of the apparatus.


I am willing to accept that Tantalum Chloride is more volatile. But the rate of corrosion of Tantalum in molten salts was given as 0.0005g/m2/day. And that seems to me as a very low number. Would that still justify your concern? The actual rate of production will in part determine the rate of contamination with Tantalum Chloride. By reducing this time we would further decrease the actual contamination.

Typically, Hastelloy N Type is used for molten salts. The reason for this is because it has a combination of properties that combined make it suitable for use with molten salts. This is structurally strong at high temperatures (Though molten, not boiling...) When I thought of Tantalum and did some research I saw it has some extraordinary properties. And at the same time, the concept described earlier does not need heavy piping and pressure resistance. It is all done at atmospheric pressure.

The design as described allows only for Tantalum and Argon to get in 'touch' with the salt.

Joey

[Edited on 15-5-2020 by JoeyJoystick]
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[*] posted on 15-5-2020 at 01:22


I do like this as a concept. I worked on a project about 10 years ago where we were trying to come up with an option for dealing with RO brine, as the clients licence did not allow discharge and no landfills in the state were licensed to accept wastes with high EC. We ended up going with large onsite evaporation ponds. No idea if anyone ever properly solved the problem.
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[*] posted on 15-5-2020 at 07:11


With the method you’re describing, in the best case you will end up with a product of equal purity to what you started with. Worst case you will just spend all this money to end up with a less pure product and a ruined apparatus. Either way, what you have here is a method to solve a problem that doesn’t exist. Some things that aren’t being considered:

-The energy requirements to do this are immense. The amount of electricity you’d need to heat the apparatus to the necessary temperature would make it a very expensive endeavor beyond what you’d spend on the kilos of machined tantalum you’re using for the apparatus.

-You’re making the assumption that gaseous NaCl is no more corrosive than liquid NaCl which is just a bad assumption to make when you’re proposing an idea that will cost thousands of dollars.

-You’re writing off the point that the impurities in the salt might be carried over in the distillation, saying that most impurities will still be left behind. But how do you know that? Take this CoA for Sigma’s >99.9% AR grade NaCl. https://www.sigmaaldrich.com/sapfs/PROD/sap/certificate_pdfs... As you can see, it reports iron, heavy metals, and magnesium as being <0.002%, <0.005%, and <0.001% respectively. Lead(II) chloride and magnesium chloride are both more volatile than sodium chloride, so you won’t be getting rid of those. Even so, that only accounts for <0.008% of the total mass. A tiny fraction of the 0.1% that is not NaCl. What do you suppose the rest of that is? There is likely some bromide present as well as some potassium. More things that won’t be removed by distillation.

While this is a fun thing to talk about, I wanted to make sure you understood the sheer impracticality of it, and weren’t actually planning to sink a ton of money into it. As SWIM alluded to, if you actually pursued this plan, you could easily end up feeling like tantalum’s namesake! ;)




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[*] posted on 15-5-2020 at 15:54


yup as others said, it's impractical from pretty much any point of view, if you need to purify a small amount of NaCl the best route is recrystallization, you can change the solvent, the temperature, and the time and optimize all of the variables to get perfect single crystals. an example, in the past i read somewhere (can't remember anymore where) that Faraday had a bottle of super pure benzene, purer than what would be sold nowdays to labs, simply because he didn't use distillation but crystallization to purify it (melting point 5.5 °C).
on large scales is cheaper to do a few recrystallizations and maybe in the end some fractional crystallizations of the molten salt.
if we want to go with the tantalum distillation apparatus for the sake of YOLO, add a tantalum fractional distillation column, refluxing liquid sodium chloride wouldbe cool to see if only you added a see through port able to withstand those temperatures.

salt is cheap, buy a few kilograms of it and run 10 recrystallizations, nurdrage did something like that for his aluminium nitrate, going from 90% purity to 99.9% (not real numbers but you can see the difference between the 2 products). you could then send the normal salt and the recrystallized one to a lab and test for trace metals and ions to see the improvement





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[*] posted on 15-5-2020 at 16:13


Hi Guys, Thanks for your response. These are the answers I was looking for. Since I did not get this response after the initial question, but merely an outlining of the near impossibilities of making such a device, I continued describing a device. But both the last 2 responses have properly shown why this is not the way to go. It was still fun describing how a such a device could potentially be made though.

And I have now seen 2 mentions of fractional crystallization. I have honestly no idea what this is, so I have something else to learn. But that is out of the scope of this thread. And first I gotta find out myself of course.

Again, Thanks

Joey
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[*] posted on 15-5-2020 at 16:18



Just to complicate matters you could try distilling under a vacuum (in the Ta still)

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[*] posted on 15-5-2020 at 21:30


Quote: Originally posted by yobbo II  

Just to complicate matters you could try distilling under a vacuum (in the Ta still)

Yob


Hi Yob,

I actually thought about that. lol. However, I was not trying to propose how to distil salt. I asked if it had been done and what the benefits of this would be, if any. And since the first responses concentrated on the impossibilities of making such a device without addressing the actual question, I figured that I should show that I think it is at least possible to make such a device. And conceptionally, the proposed device is actually very simple. It's just that the making of anything out of tantalum is not simple. But to address your question. Doing this in a vacuum would seriously complicate matters I think. I looked for melting and boiling points under vacuum, but I can't find anything on this.

But the last 2 responses before you were both constructive and showed better alternatives. And this was the answer to my initial question. So I'm a happy boy.

Joey
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[*] posted on 16-5-2020 at 01:59


Was Ta something you just stumbled on, or a lone result of systematic search?
Liquid NaCl is routinely handled above 801 Celsius (melting point!) and at fairly aggressive conditions (anodic corrosion!) because that´s the standard way to produce Na.
Which materials are suitable for molten NaCl electrolysis at 801 Celsius at which positions - reaction vessel, cathode, anode?
Precisely why do they resist corrosion by molten NaCl?
Which of them would lose the resistance by boiling point (1450 Celsius), which of them would still be suitable?

Commercial electrolysis of molten NaCl uses Fe for cathode and screen, and C for anode. Those are, however, cheap materials. How quickly are these replaced at 800 Celsius? How much Fe and C impurities do they give off, and where?
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[*] posted on 16-5-2020 at 12:51


Quote: Originally posted by chornedsnorkack  
Was Ta something you just stumbled on, or a lone result of systematic search?
Liquid NaCl is routinely handled above 801 Celsius (melting point!) and at fairly aggressive conditions (anodic corrosion!) because that´s the standard way to produce Na.
Which materials are suitable for molten NaCl electrolysis at 801 Celsius at which positions - reaction vessel, cathode, anode?
Precisely why do they resist corrosion by molten NaCl?
Which of them would lose the resistance by boiling point (1450 Celsius), which of them would still be suitable?

Commercial electrolysis of molten NaCl uses Fe for cathode and screen, and C for anode. Those are, however, cheap materials. How quickly are these replaced at 800 Celsius? How much Fe and C impurities do they give off, and where?


Uhhm. You can see in the timeline between posting my initial question and opting the idea of a vessel from Ta that there is was not that much time. I had read about molten salt on several occasions. And this in regard to 2 different subjects. The first one is what your talking about, the electrolysis of molten salt to produce Na and the other was the use of molten salts as a coolant for nuclear reactors. They tend to use different salts here. Anyways, The material developed for the distribution of molten salts is Hastelloy N Type. So when I started to look at making a distillation vessel for salt I first looked at this. Only to quickly realize that this would not be an option because of the temperature. When looking at the specs of this particular Hastelloy I saw the mention of Ta and looked a little deeper into this. I stumbled upon a document that noted that the corrosion rate for molten salt was 0.0005g/m2/day and this did not look bad to me. I already knew that the melting point was >3000c. So I looked no further. To say I stumbled upon it may be a bit of a stretch, but I did not research it much deeper than that. Mind you. I was merely trying to show that it would be feasible.

One of the responses states that I assumed that the rate of corrosion at boiling point was the same as at melting point. The truth is that I could not quickly find any information on this what so ever. So even though I did not assume that, I kinda ignored that for the sake of convenience. Now I am not on the same level as many of you here in the forum. And sometimes I go by my guts. In this case my guts told me that the corrosion rate was probably higher but considering the low rate of corrosion of Ta for molten salts I figured I would probably get away with it in a gaseous state. I have no way of substantiating this claim. But I wanted the responses to move away from the impossibilities of making this device and focus on the question. Which, quite frankly, it did.

As far as the use of carbon and, especially, Fe for the electrode and cathode in molten salt for the production of Na I really had to stop and think. I searched for this as well. But it is not that easy to find detailed design consideration for this. I figured that it had to do (sorry here my English lags. I am searching for the right word) with the potential difference between anode and cathode. And to make a crude comparison, I looked at is as a Zinc cathode on a ship to avoid corrosion. Both of them easily corrode in Salt water. But the voltaic difference between the 2 saves the steel and concentrates the corrosion onto the Zinc. You get my drift here right?

But there is a few more internals inside a molten salt reactor for Na electrolysis and I figured that the rest could not possibly be made of iron and/or carbon. Nor steel. And though I never figured out what material is used for the internals, I am guessing that this is some kind of Hastelloy. Since they normally operate at about 600C and not 800C this is probably not N Type, but I am really just guessing and thinking out loud without knowing the answer for sure. I find it hard to believe that this would be iron or even carbon steel. I strongly believe that the iron will wear down and I also think that the wear down rate may be influenced by the electrolysis process.

You mention contamination by C and Fe. I don't think that's the case for a distillation apparatus simply because there is no electrolysis. I feel (you did not explicitly say that though) that you're wondering why the heck I would wanna use Ta if I can Fe. I think that difference is the electrolysis. And the need to avoid contamination, or at least that was my idea.

Joey
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[*] posted on 16-5-2020 at 13:00


[Edit]

Now it shows the original message properly, but I did not do anything. Did I do something wrong or is there a bug somewhere?

[End Edit]

I don't understand why my first alinea is chopped in half, but here it is in full.

Uhhm. You can see in the timeline between posting my initial question and opting the idea of a vessel from Ta that there is was not that much time. I had read about molten salt on several occasions. And this in regard to 2 different subjects. The first one is what your talking about, the electrolysis of molten salt to produce Na and the other was the use of molten salts as a coolant for nuclear reactors. They tend to use different salts here. Anyways, The material developed for the distribution of molten salts is Hastelloy N Type. So when I started to look at making a distillation vessel for salt I first looked at this. Only to quickly realize that this would not be an option because of the temperature. When looking at the specs of this particular Hastelloy I saw the mention of Ta and looked a little deeper into this. I stumbled upon a document that noted that the corrosion rate for molten salt was 0.0005g/m2/day and this did not look bad to me. I already knew that the melting point was >3000c. So I looked no further. To say I stumbled upon it may be a bit of a stretch, but I did not research it much deeper than that. Mind you. I was merely trying to show that it would be feasible.

Joey

[Edited on 17-5-2020 by JoeyJoystick]
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[*] posted on 18-5-2020 at 15:25




Is molten salt conductive?
If it was you could have an ark disccharge going into the melt and then you could use an air cooled vessel. The actual vessel holding the melted salt is ...... salt.
The container would be very hot no doubt but relatively cool on the outside. The salt would form a skull inside the container and the salt being distilled (the boiling salt) would be contained in this salt skull. Something similar is done with very high melting materials that really have no container that will hold them.
The carbon (I presume you would have to use carbon) ark rod might contaminate things.

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[*] posted on 18-5-2020 at 19:49


https://www.ebay.com/itm/Harshaw-NaCl-Sodium-Chloride-Cylind...

So would something like that be tremendously pure?

[Edited on 19-5-2020 by SWIM]

I bet you could talk them down a bit as the thing has a crack in it which I assume would be a problem for laser use.

[Edited on 19-5-2020 by SWIM]




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[*] posted on 18-5-2020 at 21:47


Quote: Originally posted by yobbo II  


Is molten salt conductive?
If it was you could have an ark disccharge going into the melt and then you could use an air cooled vessel. The actual vessel holding the melted salt is ...... salt.
The container would be very hot no doubt but relatively cool on the outside. The salt would form a skull inside the container and the salt being distilled (the boiling salt) would be contained in this salt skull. Something similar is done with very high melting materials that really have no container that will hold them.

That works when all you want is melting. Heating from melting to boiling point is the hard part.

The unwanted corrosion reaction is something like:
4Ta+5O2+20NaCl+10CO2->4TaCl5+10Na2CO3
Note that your Ta apparatus can also easily corrode off on the outside:
4Ta+5O2->2Ta2O5
Of the refractory metals, Pt is pretty stable to air oxygen - a thin layer of oxides forms at a few hundred Celsius, but at higher temperatures it decays. There are a number of substances known to attack Pt, such as P and As, but molted salt is not listed among those.
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