I moved the posts I made on Ralph's membrane thread here. His cell is really neat and well-made and I hijacked his thread. Sorry, Ralph
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Bullion.Forum
Membrane Systems
- Thread starter goldsilverpro
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If anyone recalls, I promised a write-up on a nitric making cell about 5 years ago. Better late than never, I guess.
Your tank is basically the same configuration as the tanks I built in the early 80s - one was about 100 gallons. How did you secure the membrane to make it leakproof? If the materials used can withstand nitric and sodium hydroxide, you can use a 3 cell system with 2 ion-exchange membranes to make HNO3 and NaOH at the same time using sodium nitrate.
From left to right:
- 300 series SS Anode (+) at far left - 304L is probably best
- Weak nitric solution (say, 2%) in left cell to make the solution conductive and get it started
- Anodic membrane (will only pass anions - those with a minus sign like NO3-)
- Sodium nitrate solution in middle cell
- Cathodic membrane (only pass cations - like Na+)
- Weak NaOH in right cell
- SS cathode at far right (-)
Use distilled water in each cell.
Here's what happens:
When you turn the current on, all the (-) ions are attracted to the left to the anode (+) and all the (+) ions are attracted to the right to the cathode (-). Unlike charges attract.
At the same time, water is split at both electrodes. At the anode, oxygen is given off as a gas and H+ ion enters the solution in the left cell. At the cathode, hydrogen gas comes off and the OH- ion enters the cell on the right.
NO3- (middle cell) and OH- (right cell) are both attracted to the left towards the anode. The NO3- passes through the anodic membrane into the left cell. The OH-, however, stays in the right cell because it won't pass through the cathodic membrane. In the same vein, the H+ stays in the left cell (it is blocked by the anionic membrane) and the Na+ passes through the cathodic membrane from the middle cell to the right cell.
The result is that H+ and NO3- (HNO3) build up in the left cell, Na+ and OH- (NaOH) build up in the right cell, and the Na+ and NO3- (sodium nitrate) becomes depleted in the middle cell. You just add NaNO3 to the middle cell periodically and bail out the left and right cells periodically.
If you want to make HCL and NaOH, you use NaCl in the middle cell, although that might not work too well due to Cl2 coming off as gas at the anode. To make H2SO4 and NaOH, you use sodium sulfate in the middle cell.
A problem with the nitric is that I haven't found an anionic membrane that will stand up to nitric in excess of about 20%. Dupont makes a teflon cathodic membrane but not an anionic one. I think someone makes them, though. Japanese companies make a big variety of interesting membranes. One is a membrane that will only pass +1 ions (by Asahi Glass, I seem to remember). Separate Ag+ from Cu++ and other higher charged positive ions. There are also bipolar membranes (they work a bit differently) that can be used to make the acids/NaOH (or, whatever you want to make).
Ion-exchange membranes are sometimes called ion traffic controllers.
Your tank is basically the same configuration as the tanks I built in the early 80s - one was about 100 gallons. How did you secure the membrane to make it leakproof? If the materials used can withstand nitric and sodium hydroxide, you can use a 3 cell system with 2 ion-exchange membranes to make HNO3 and NaOH at the same time using sodium nitrate.
From left to right:
- 300 series SS Anode (+) at far left - 304L is probably best
- Weak nitric solution (say, 2%) in left cell to make the solution conductive and get it started
- Anodic membrane (will only pass anions - those with a minus sign like NO3-)
- Sodium nitrate solution in middle cell
- Cathodic membrane (only pass cations - like Na+)
- Weak NaOH in right cell
- SS cathode at far right (-)
Use distilled water in each cell.
Here's what happens:
When you turn the current on, all the (-) ions are attracted to the left to the anode (+) and all the (+) ions are attracted to the right to the cathode (-). Unlike charges attract.
At the same time, water is split at both electrodes. At the anode, oxygen is given off as a gas and H+ ion enters the solution in the left cell. At the cathode, hydrogen gas comes off and the OH- ion enters the cell on the right.
NO3- (middle cell) and OH- (right cell) are both attracted to the left towards the anode. The NO3- passes through the anodic membrane into the left cell. The OH-, however, stays in the right cell because it won't pass through the cathodic membrane. In the same vein, the H+ stays in the left cell (it is blocked by the anionic membrane) and the Na+ passes through the cathodic membrane from the middle cell to the right cell.
The result is that H+ and NO3- (HNO3) build up in the left cell, Na+ and OH- (NaOH) build up in the right cell, and the Na+ and NO3- (sodium nitrate) becomes depleted in the middle cell. You just add NaNO3 to the middle cell periodically and bail out the left and right cells periodically.
If you want to make HCL and NaOH, you use NaCl in the middle cell, although that might not work too well due to Cl2 coming off as gas at the anode. To make H2SO4 and NaOH, you use sodium sulfate in the middle cell.
A problem with the nitric is that I haven't found an anionic membrane that will stand up to nitric in excess of about 20%. Dupont makes a teflon cathodic membrane but not an anionic one. I think someone makes them, though. Japanese companies make a big variety of interesting membranes. One is a membrane that will only pass +1 ions (by Asahi Glass, I seem to remember). Separate Ag+ from Cu++ and other higher charged positive ions. There are also bipolar membranes (they work a bit differently) that can be used to make the acids/NaOH (or, whatever you want to make).
Ion-exchange membranes are sometimes called ion traffic controllers.
Attachments
When I started working with membranes, I was able to get free samples (usually about 6"X6") from the companies that sold them. Some membranes (Ionics, for one) have to be stored in water because they will crack when dried out.
I spent about 2 years playing with membranes. I used to fill notebooks with sketches (similar to the drawing above) of the 100s (literally) of interesting things you could try doing with membranes. I had an AA with most every lamp and lots of titration stuff to monitor ion transference in the various cells. All this became an addiction!
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This is hard to explain without a drawing, but I'll try.
For experimental purposes, I obtained a bunch of about 250ml open top, square, tall boxes (say, 2"x2"x4" tall) made from a very rigid, hard clear plastic (Styrene? Acrylic? I don't remember). Each box was an individual cell.
In the above 3 cell example, I cut 1 window (say, 1" x 2") centered on one side of the left and right boxes and 2 windows in the middle box, one on each side, using a Dremel tool. The windows were all the same size and were in identical positions on each box. The membranes were about 1/4" larger than the window on all 4 sides.
I then applied grease (silicone? or teflon?) to the 1/4 border (only!) on both sides of the membranes. The membranes were then positioned over the windows and the 3 cells were lined up perfectly. To hold the 3 cells together, I used a couple of heavy rubber bands. The grease sealed the membranes around the windows and prevented leaking.
I remember having as many as 7 of these boxes (cells) ganged together, with different solutions in most of the cells, for certain wild experiments. Usually, everything happened as per my sketch predictions.
I spent about 2 years playing with membranes. I used to fill notebooks with sketches (similar to the drawing above) of the 100s (literally) of interesting things you could try doing with membranes. I had an AA with most every lamp and lots of titration stuff to monitor ion transference in the various cells. All this became an addiction!
_____________________________________________________________________
This is hard to explain without a drawing, but I'll try.
For experimental purposes, I obtained a bunch of about 250ml open top, square, tall boxes (say, 2"x2"x4" tall) made from a very rigid, hard clear plastic (Styrene? Acrylic? I don't remember). Each box was an individual cell.
In the above 3 cell example, I cut 1 window (say, 1" x 2") centered on one side of the left and right boxes and 2 windows in the middle box, one on each side, using a Dremel tool. The windows were all the same size and were in identical positions on each box. The membranes were about 1/4" larger than the window on all 4 sides.
I then applied grease (silicone? or teflon?) to the 1/4 border (only!) on both sides of the membranes. The membranes were then positioned over the windows and the 3 cells were lined up perfectly. To hold the 3 cells together, I used a couple of heavy rubber bands. The grease sealed the membranes around the windows and prevented leaking.
I remember having as many as 7 of these boxes (cells) ganged together, with different solutions in most of the cells, for certain wild experiments. Usually, everything happened as per my sketch predictions.
One time I tried to create a solution whose total charges were out of balance - where the total positive charge was more or less than the total negative charge. A new fuel maybe. I think I used 7 cells in a row. However, nature wouldn't let me do it although the setup I had was correct. At the bottom of each of the 6 membranes, which were not conductive!, I could see the bubbles from water splitting. This provided enough of the missing ions to keep all the charges in balance. In no other experiment did the water split anywhere but on the electrodes.
Did you mean to post a link?Palladium said:
They sound OK but I don't know There are probably 100 more companies making these now than 35 years ago when I was messing with them. Back then, it seemed like each company's products were made of different materials.Palladium said:
Were it me, I would get on the phone and start begging for samples. Get their prices in square feet and in volume. A business name and address would very likely help. After all, you will need a lot of these in the future and you're surely not going to buy from them if their product doesn't work. I used to be the king of getting free samples.
To me, the most important thing is what they are made out of and will they withstand the chemicals I want to use. It would be great if they were all made of Teflon or other fluorocarbon, but they're not. The only ones I know of are the Dupont Nafion Cationic membranes. If they also made Teflon Anionic membranes, the nitric cell problem would be solved.
solar_plasma
Well-known member
I just came to wonder, if sodium silicate and heavy metal salts could give a useful cation selective membrane. Think of the chemical garden experiment.
maybe...glas fiber cloth soaked with sodium silicate and sprayed with an appropriate heavy metal salt....
anion selective would be quite another story, though....
maybe...glas fiber cloth soaked with sodium silicate and sprayed with an appropriate heavy metal salt....
anion selective would be quite another story, though....
I know there is a lot of information out there on making membranes, including a lot of patents, but I never really studied that part of the literature.solar_plasma said:
There are also a lot of patents, mostly from the 70s and 80s, that utilize membranes in PM recovery schemes. I run into them every so often when I'm researching patents. At that time, membranes were new to most people. They were a hot item and it seemed that most refineries were experimenting with them.
The widely available bipolar membranes are very interesting, in that they can do wild things that the regular membranes cannot do. I would certainly research them. I have not used them.
Here's a schematic on the small plastic box-cell arrangement mentioned above. You just assemble the cells as shown, clamp the whole thing together with big rubber bands and put an electrode in each end. The holes (windows) should be relatively bigger, though. The more membrane surface area, the lower the voltage will be for a given amount of current. I might improve the drawing and re-post it.
Attachments
I know enough to know that bipolar membranes are the cat's meow. I just don't know enough to intelligently discuss them. I'll learn, though. They weren't around much when I did the membranes. Just don't lock into one manufacturer. There are lots of manufacturers and lots of different membranes. Get lots of samples.
There's an old request in the PM refining business - Send us Bigger Samples!!!! :lol:
There's an old request in the PM refining business - Send us Bigger Samples!!!! :lol:
rickbb
Well-known member
I've seen designs that use a "salt bridge" as a membrane. They make this salt bridge out of gelatin and table salt. It's setup in a PVC tube that connects the different tanks.
I wonder if this type of technology could be used to turn potassium perrhenate into perrhenic acid and KOH in a compartmented cell?
What do you think Chris?
What do you think Chris?
goldsilverpro said:
This should help. My head hurts! :arrow:
The old technology will work but the efficiency, membrane leakage (Contamination between cells), and the anodes-cathodes, are parameters that are hell to deal with. I'm looking into not only the bipolar membrane technology, but also using PWM to control the water splitting sort of like in an hho cell. This could get real interesting. I love science!
I follow you. Sounds like it will work. Essentially the same as making nitric.Lou said:
Salt bridges are interesting. I've read about them. I just don't know enough to discuss them. I can learn, though.rickbb said:
