Manufacture of sodium hydroxide

[hereticalhermit]

I have an old chemistry book, which describes one of the earlier methods of manufacturing NaOH. Doing a search on the manufacture of NaOH, both here and on the internet, I am able to find information on the process using mercury ("Kastner" cells), but almost none on the older method using "Vorst" cells. What I have been able to find on the internet are merely references to people having worked with them in the past wherever those people may have been employed.
A "Vorst" or "diaphragm" cell is useful for making NaOH when electricity, water, and salt are the only items available to use for the process. It consists of one perforated cell, an asbestos diaphragm, another metal container outside of those, and a catch-basin for the lye. The inner cell is filled with brine, electricity is applied, and a mixture of brine and lye fills the bottom pan, while hydrogen and chlorine are produced at the terminals. The strength of the lye is low, and it needs to be further refined.
Using asbestos as the diaphragm is no longer an option, and some research has been done on other materials, but most of that research is not public information, or the materials are either proprietary or very expensive. Class "c" fiberglass may be a possibility.
Has anyone out there had any experience with this type of electrolytic cell?

[megalomania]

A long time ago I made NaOH by electrolyzing salt water using a terra cotter flower pot as the ion bridge, which was in turn placed inside a 5 gallon plastic bucket filled with water. I let the thing run for weeks and I barely got anything. Worse still, because it was exposed to the air for so long I ended up with a good deal of sodium carbonate (CO2 pulled from the air neutralizes the sodium hydroxide solution slowly).

I used a low current power source, which led to such a low yield. Faraday's law tells us why this happens, the more electrons flowing into the system (current) the more product you get. With a high current, low voltage power source I could have made NaOH much quicker.

This method is not nearly as efficient as the electrolysis of molten salt (giving sodium metal which is then chucked into water), but it is something people can actually build with minimal materials.

I once read about a cell divider, I believe in one of the early 20th century technical recipe books collections. You make a divided cell out of concrete. You need a fine concrete, like a mortar or grout even, thoroughly mixed with large amounts of salt. The salt should be a fine granulated type like table salt, not rock salt or finely powdered.

You mix up the concrete as normal and pour it into a mold. A cardboard mold shaped to fit your container would be great. For example you can glue or caulk plastic strips on the inside of a bucket to make a channel, then the concrete plate slides in like a window slides down in a frame. The concrete plate should be thin, maybe 1/4 inch to 1/8 inch thick.

Allow the concrete to dry fully, then submerge the plate in water for... lets say a week or two. The immersion leeches out the salt trapped in the plate giving a very porous structure. This porous plate is an excellent barrier for electrolysis purposes.

I am not too sure on the granularity of the salt. It may need to be either very finely powdered, like dust, or perhaps ground a little finer than table salt. The resulting voids need to be big enough to make connecting channels. If the salt is too fine it will be trapped and isolated in the concrete, and if it is very course the voids will allow ions to just pass right through.

Such a plate is cheap, not terrible difficult to make, and it is very effective. It may become fouled over time by undesired ions like a clogged filter. You can just make a new one, or run the electrolysis system in reverse. This is what a big manufacturing operation would do, it is probably not worth the time and trouble considering it is easier to make a new one if it is small.

Obviously there are limits on the size of the plate. Make it too thin and it will not stop ions from passing right through. Make it too thick and you will waste more and more energy pushing your ions through. Since these need to be operated horizontally, making it too big could cause it to crumble. On the 5 gallon bucket scale, a quarter inch should be fine.

[rangegal]

How they made soap in the old days! Hardwood ash was mixed with water and filtered, then evaporated down till it was concentrated enough to "dissolve a feather". If you have a wood burning stove or heater you use (quite common where I live) or you just like campfires, you already have a lot of source material! I have NO idea what the yield is like but you'll need to find a way of purifying it since there will be a mix of potassium hydroxide, sodium hydroxide, and other alkalis.

Its not the easiest method out there these days, but it worked for alchemists.

[megalomania]

That information is already on The Forum somewhere... I think there might be something about that in the Dick's Cyclopedia, perhaps the caveman chemistry books (the old material that was completely free before the cocksuckers turned it into a paysite).

I don't recall the exact particulars, but I know I have read this in one of the books available online, the FTP, and somewhere on my harddrive: From the Poor Man's James Bond, I think, there are the instructions about boiling and filtering wood ash to collect the potassium carbonate. Then there is something about making this into sodium carbonate, then precipttating the carbonate with lime giving sodium hydroxide.

Hmm, I think I am referring to mixing baking soda and lime to make sodium hydroxide. That might be in the Golden Book of Chemistry Experiments... There it is, page 45:

Bases from a Salt
In a custard cup, dissolve 1 teaspoon sal soda (washing soda, sodium carbonate) in 50 mL water. Heat slightly. Add slaked lime mixed with water. Stir. Chemical reaction produces sodium hydroxide and calcium carbonate. Filter. Clear liquid contents contains the sodium hydroxide (lye). The calcium carbonate is held back by the filter.

I like that writing style, very straightforward and clean. Many of my classmates would have avoided trouble if the damn writeup specified which extract or filtered portion held the good stuff and which could be discarded. One of these days it will get me too.

You can make your own sodium carbonate from baking soda by boiling, but you can buy "washing soda" in the laundry detergent section in a large box. Made by the same people who make baking soda... I provide this info because I don't know what the price of a box of washing is vs. baking soda. I know baking soda is very cheap, and if you are in this game to make a ton of sodium hydroxide (literally) you may want to crunch the numbers and figure out if the time spent making your own sodium carbonate from sodium bicarbonate is worth it.

Purity wise your final sodium hydroxide will be as pure as the lime. You can buy pickling lime of high purity, and retail baking soda and washing soda are already pure; all of these compounds are food grade, which means you could make some very high quality sodium hydroxide. Even if you used construction grade lime, most of the impurities are insoluble.

[James]

I was thinking a little and it occurred to me that both the molten salt electrolysis and Megalomanias' terracotta pot method might have less chance of forming unwanted byproducts if carried out in a glove box type deal w/ say an inert (say nitrogen or argon) atmosphere. possibly with a small rig inside to scrub the Chlorine say bubble the off gassing through a neutralizing solution.
I was thinking of saying something like a pressure cooker, but that would be too kewl I think.

[megalomania]

Actually, taking a cue from homebrewers, if you use a plastic bucket to hold this, you can attach the lid. You can improve things with one of those one way valves brewers use during fermentation to exclude air. I think there are even 5 gallon lidded buckets with those valves already attached. Wire connections for electrodes can be passed through the lid and sealed with caulk.

You should not even need any other atmosphere. The chlorine gas, and other stinky crap the reaction can form depending on your voltage and concentration, will produce a positive pressure that escapes out the valve. If you compartmentalize the sodium hydroxide, you can prevent chlorine from dissolving into it and forming salt + other byproducts.

One thing I would like to try is the "solid oxide membrane" process of making metals. I collected a few nifty articles about this for magnesium production, and presumably it will work for sodium metal too. From sodium metal, of course, sodium hydroxide can be made. These suckers use molten copper metal in a special ceramic tube immersed in molten salt to electrochemically form the metal.

Assuming you can make or buy the special ceramic tube, this type of reaction might put molten salt electrolysis on the DIYers table.

[kolraw]

Megalomania,

In your description of an electrolysis cell to make NaOH you seem very intent on making a good ion bridge for your cell.

Let me first check that I have things straight.

-We're making NaOH.

-At negative cathode:
2e + 2H20 --> 2OH- + H2

-At positive anode:
2Cl- --> Cl2 + 2e

-All together now:
2NaCl + 2H20 --> 2NaOH + Cl2 + H2

-We've got some sort of high current, low voltage (~2.5V across cell) power source.

To my knowledge the ion bridge completes the cell's circuit, and stops the contents of the two half cells mixing, but it seems that the contents of the half cells wouldn't really do any strange side reactions.

So, I was wondering why this setup needs a semi permeable ion bridge, wouldn't it function with straight electrolyte seperating the electrodes?

(By the way if you collected the H2 and the Cl2 you could pretty easily make HCl, couldn't you?)

[kolraw]

Ignore my previous post. I realised overnight that H20 is a better reductant than Cl2 so the cell would look like this:


-At negative cathode:
2e + 2H20 --> 2OH(-) + H2

-At positive anode:
2H20 -->4H(+) + 02 + 4e

-All together now:
6H20 --> 4OH(-) + 4H(+) 02 + 2H2(NaCl electrolyte)

So the ion bridge keeps the OH(-) from mixing with the H(+) produced and doesn't ruin your hard spent energy. The Na(+) moves to the OH(-) side and the Cl- moves to the H(+) side. Correct me if I'm wrong but you get NaOH at the cathode and (it seems to me) HCl at the anode.

Idiot me! *head in hands*
I hope I have it right now.

[waveguider]

How they made soap in the old days! Hardwood ash was mixed with water and filtered, then evaporated down till it was concentrated enough to "dissolve a feather". If you have a wood burning stove or heater you use (quite common where I live) or you just like campfires, you already have a lot of source material! I have NO idea what the yield is like but you'll need to find a way of purifying it since there will be a mix of potassium hydroxide, sodium hydroxide, and other alkalis.

Its not the easiest method out there these days, but it worked for alchemists.

Wrong.
there is practically no NaOH in ashes, the majority of wood ash that is soluble is Na2CO3 and K2CO3 (more soda lime in ash at sea side and in seaweed ash). You can roast these to produce their corresponding (oxides) then hydrate to form the hydroxides much like how lime was made in kilns.
http://www.fryingcolors.com/k2co3.html
Or If you react Na2CO3 with CaOH (calcination of limestone) however you get NaOH for use in soap making. This reaction forms a precipitate of limestone which makes purification easy. I'm not sure on this reaction, would love if someone confirmed it.

[Jome skanish]

Couldn't the Na2CO3 be used to oxidize carbon, such as 2Na2CO3+C --->4Na + 3CO2, giving sodium or, if lower temps are used, perhaps CO, CO2 and Na2O?

Found this procedure while searching for a plausible ancient method of producing sodium metal, I'll see If I can find a reference....

[t.shonku]

Simple way of making NaOH:

It is done by adding Ca(OH)2 (calcium hydroxide) to a solution of Na2CO3 (washing soda). Then heating the entire solution. After some time the solution is allowed to cool, filter to remove CaCO3 , then the filtered solution
is evaporated to obtain NaOH.

The equation is----Na2CO3 + Ca(OH)2=2NaOH + CaCO3.

+++++++++++++++++
You spelling and grammar is appalling. If I need to re-write your posts again, you are gone. - totenkov

[tranquillity]

kolraw: You were actually right the first time. Cl2 is produced in saturated NaCl solutions as you would use for electrolysis. This is because reduction potentials are dependant on concentration and are reduced as concentration increases, making 2Cl- --> Cl2 + 2e- the preferred reaction. The Nernst equation can calculate reduction potentials at non-standard conditions.

Jome Skanish: I do not think sodium metal could be obtained by heating Na2CO3 with carbon as is used for metals like iron. I was speaking to someone recently who is working on a process for producing magnesium metal by reacting MgO with C at high temperatures. Apparently to make that process work they heat the mixture so everything is in the gas phase as CO and Mg then have to cool it again in much less than 1s (I think he said 0.0001s but dont recall specifically) to get a useful product. If it is cooled slowly they just end up with C and MgO again. I guess it would be even harsher conditions to get sodium.

As a side note which may be of interest to some: The Mg process I described produces extremely fine and reactive Mg powder which is capable of exploding with only air as the oxidiser. Perhaps if it could be desensitised enough without hurting reactivity it would make an excellent pyro metal powder.

[fluoroantimonic]

I do not think sodium metal could be obtained by heating Na2CO3 with carbon as is used for metals like iron.

Surprisingly it does work. I didn't think it would either, but search patents and you will find many on the subject of producing Na metal from Na2CO3 or NaOH by reduction with hydrocarbons or coke at high temperatures. Usually around 900*C in the liquid phase IIRC. The gaseous Na must be cooled relatively quick to avoid too much Na2C2 formation though (I think a few seconds is no problem). It is usually done by injecting a spray of mineral oil into the gas. I think this method might not be a bad way to go for the amateur that needs some sodium. At least it's pretty simple, no catalysts or expensive reactants. Just tons of energy.. And liquid Na2CO3 is apparently pretty corrosive so a good crucible material would have to be worked out.