Membrane Systems

[solar_plasma]

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.

This sounds as something useful and easy done for school experiments. Can you remember what anions it will work for? I would have expected, that it doesn't work with NO₃^- or SO₄^--, since gelatine is a protein, which turns yellow by nitric, and sulfuric removes water from many organics. Another problem, I see, is, that gelatine slowly dissolves in water, especially when warm.

Chloride should work. At least when a chicken bone is left in HCl, only the gelatinous (don't know, if this actually IS gelatine) components will be left structural intact.

 

[rickbb]

I ran across the salt bridge when looking up making sodium hydroxide in a cell. The various article's claim that in this process the gelatin will not dissolve.

 

[Palladium]

I found the company who supplied the membranes for a prototype salt splitting cell for NASA that uses salts to produce chemicals while in space. I can order samples directly from them, but they think highly of the price! I would rather go with the best than miss my mark based on price though. Looks like about $200 when all is said and done for 3 pieces the size of sheets of paper. (1 cation. 1 anion. 1 bipolar membrane). It this works then i feel we have found a process to safely produce nitric acid from salts and water. They claim with this process levels of 68% can easily be reached. I'm going to make a bench top nitric acid machine! From my estimates 1 gallon 68% every 24 hours should be an easy goal.

http://www.fumatech.com/EN/Onlineshop/fumasep-for-Electro-membrane-processes/

 

[rewalston]

now that would be interested Ralph for those of us having a hard time getting Nitric Acid.

Rusty

 

[necromancer]

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.

This sounds as something useful and easy done for school experiments. Can you remember what anions it will work for? I would have expected, that it doesn't work with NO₃^- or SO₄^--, since gelatine is a protein, which turns yellow by nitric, and sulfuric removes water from many organics. Another problem, I see, is, that gelatine slowly dissolves in water, especially when warm.

Chloride should work. At least when a chicken bone is left in HCl, only the gelatinous (don't know, if this actually IS gelatine) components will be left structural intact.

you may be thinking of "cartilage"
http://en.wikipedia.org/wiki/Cartilage

 

[necromancer]

now that would be interested Ralph for those of us having a hard time getting Nitric Acid.

Rusty

nitric acid is easy to get here in Ontario in large amounts, small amounts are to expensive & chemicals to make nitric without distilling are impossible to get. (Potassium Nitrate, Sodium Nitrate)

i can buy a carboy of nitric acid but it will last me way to long.

 

[eastky]

I found the company who supplied the membranes for a prototype salt splitting cell for NASA that uses salts to produce chemicals while in space. I can order samples directly from them, but they think highly of the price! I would rather go with the best than miss my mark based on price though. Looks like about $200 when all is said and done for 3 pieces the size of sheets of paper. (1 cation. 1 anion. 1 bipolar membrane). It this works then i feel we have found a process to safely produce nitric acid from salts and water. They claim with this process levels of 68% can easily be reached. I'm going to make a bench top nitric acid machine! From my estimates 1 gallon 68% every 24 hours should be an easy goal.

http://www.fumatech.com/EN/Onlineshop/fumasep-for-Electro-membrane-processes/

I would be interested in helping out with the cost of doing a cell for nitric acid. If interested send me a pm.

 

[Palladium]

Dam! Time for a go fund me account! :mrgreen:

Believe it or not that's how i do a lot of my designs for clients is with experiments on a scale model. The client usually covers the cost of the equipment and i donate my time and effort. When this is said and done it will probaly cost $ 350-400 for the first model at cost and then price drops as production gets efficient. I could sell them for $1,000 and do good. This will be the third experiment i'm working on right now. The first is the fizzer cell. The second is the new design for the silver cell, and the third would be the membrane cell. I really like the membrane idea on a bench scale, it's just the science that goes into it may look simple in design, but is more complex in the build. I still have control mechanisms, anode and cathode selection and design considerations. Power design is complicated, but somewhat easy. With today's technology i can buy a board off ebay, jack it in to my computer with a usb, and program the electronics fairly easy. Theirs a few things i'm not sure of yet, but that's why i build things that can be controlled by parameters so it can be adjusted. You can do the same thing with regular membranes, but the longevity, product percentages, maintenance, energy cost, and all the other problems compound into " This thing sucks! ". I won't build or sell junk! That's what ebay is for.

Wait! I'm on Ebay. :twisted:

 

[butcher]

I have given thought to this idea several times but never followed through with any ideas,

Salt bridges will work fine for ionic salts like sodium or nitrate and so on, but trying to move hydrogen or a gas across the bridge just wont work.

I have also thought that we might be able to use a gas evolved from say one cell and add it to another cell to chemically react to form a product in that compartment...

I have made several drawing on paper of different ideas, I tried to put one on paint program(never used it before), this Idea is using a 3 compartment cell (two separate power supplies), here the center electrode could be one common electrode if wanted.

 

[Palladium]

Got some samples in today (6X6). It's not the bipolar membranes i need, but it's something fun i can play with to learn before i drop a couple hundred on the other ones and screw them up from inexperience! :mrgreen:

 

[Lou]

I'm interested to see how this all develops. If Ralph can make a nice compartmented membrane cell...should be cool. This means that members can dissolve their silver, remove it with just enough chloride, waste treat the barren nitrate solution, filter, and re-use that sodium nitrate solution to make more nitric!

I know divided membrane cells are how NaOH is now made in bulk--on 3500# containers we get in, it says "diaphragm grade". Time was when all the NaOH and chlorine made from brine was made using mercury cathodes. No longer! At least here in the US. Nice to see technology make things a little more environmentally friendly.


Lou

 

[Palladium]

Membranes use to intimidate me until i got a better understanding of them. I have read stuff until my head hurts. You're right! The technology is fascinating. Advanced as the industry is today it's still a specialty market that's still in it's infancy, at least for the bipolar membranes. The problem lye's not in the science or theory, but in the manufacturing of the membranes themselves. From what i read with dealing with waste streams or multi metals solutions the problems come from fouling of the membranes. So many variables to account for in a complex system like that. For years they have used membrane technology in different types of salt splitting cells, but the problems have been drift through the membranes which leads to contamination of the final product and lower levels of solution concentrations. Anode design suffers from degradation, fouling, excess gas generation, heating, and inefficiency of electrical energy conversion. With the bipolar membrane it virtually eliminates all of that. The science behind the bipolar membrane and the physics involved are both complex...... yet simple! With a simple salt splitting cell (bipolar) using just two elements combined as a salt to generate separate solutions the longevity, durability, as well as the simplicity should be fairly easy to demonstrate for everyday use by members or anyone who needs acids on demand. Nasa had a prototype built that seems to fit the bill so i figure why not me! :mrgreen:

 

[goldsilverpro]

Ralph,

There's a lot of PM patents using membranes. Here's a couple of searches. Electrodialysis membranes and ion-exchange membranes are essentially the same thing.
https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=gold+recovery+membrane&num=10#hl=en&tbm=pts&q=gold+recovery+membrane+electrodialysis

https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=gold+recovery+membrane&num=10#hl=en&tbm=pts&q=gold+recovery+membrane+ion-exchange
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When fabricating a membrane cell, the most important part is seal them so that there is no leakage from one chamber to another. This is easier said than done. All materials used must stand up to whatever types and strengths of chemicals are in the chambers.

During the 2 years I played with membranes, I used only 2 methods for sealing off the chambers:

(1) For the small (~200ml) experimental cells I discussed earlier in this thread, I cut windows in the boxes (polystyrene, I think - very rigid) and sealed the membranes between boxes with grease that was inpervious to the chemicals. Rubber bands clamped the line of boxes together. This method is easy with a fast setup and allows you to use any number of chambers that your heart desires. I mentioned that I once used 7 chambers and each was needed in the weird-ass experiment I thought up.

I once thought about building and selling a larger version of this, maybe with one gallon chambers, using a strap ratchet clamp. Besides chemical resistance, the most important thing is that the walls of the individual tanks (chambers) are rigid enough to prevent distortion of the walls when clamped. This could cause leakage.

Thick (1/2"?) plastic sheet welded into 1 gal. tanks would work. I also thought of, say, 1/8" thick stainless tanks with a plastisol coating. I used to buy a liquid plastisol by the gallon that was made for plating fixtures. I used it to dip coat small plating racks.

(2) Big tanks. The biggest one I made was about 100 gallons. I was dissolving superalloys in weak sulfuric anodically. A membrane divided the tank into 2 compartments and prevented the dissolved metals from contacting the cathode. Worked great except for the significant mist of sulfuric in the air caused mainly by the fizzing at the cathode. It was so bad you couldn't go in the room. We floated about 3 layers of different sized PP mist-suppression balls on top of the cathode solution and that helped considerably.

I'll make a drawing for this sooner or later. I had the tank fabricated from probably 1/4" plastic. A flat picture frame was welded up from the same plastic, using, say, 1/2" thick x 3" wide pieces. The width of the frame was such that it fit fairly snugly in the tank. Holes of a size to take a 1/2" PVC bolt were drilled every 3", or so, around the 4 sides of the frame. The frame was welded into the tank. A slightly narrower duplicate frame with matching holes was built. We used a one piece Buna-N (I'm thinking - either that or Neoprene) rubber gasket I made (with holes) between the frame and membrane. In order: Frame in tank - Buna N gasket - membrane - loose frame. We may have also used a 2nd gasket between the other side of the membrane and the loose frame. Everything was sandwiched together and mounted using 1/2" PVC bolts, nuts, and washers.
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If I were to get heavy into this, I would surely get a good self-contained plastic welder (about $500) and learn how to use it properly - I have a little experience in this and it seems pretty easy - just control the variables - temp and flow rate of the heated air - positioning, etc. Also, with a table saw, 4x8 sheets of plastic, and a heated sheet bender, you could make your own tanks to your own specs. Saves a lot of money and puts you in better control.

 

[solar_plasma]

Today I got an anion exchanger membrane and a cation exchanger membrane from Fumatech as a free sample, both 20cmx30cm Very nice people!

I will take the time needed to read everything again, so I know exactly what and how to do before starting. Would be a shame to destroy them by stupidity.

 

[goldsilverpro]

Richard,

In your sketch, you can accomplish exactly the same thing by using just one power supply across the 2 outer electrodes and eliminate the 2 inner electrodes. I would also use NaNO3 instead of NH4NO3. That way, there would be no ammonia coming off although I'm not sure it would come off as in your sketch. Sometimes the chemical reactions at the electrodes are not that easy to predict. Actually, I like your setup (but with only 1 PS) for nitric better than the one I gave earlier, although it might be harder to control.

Instead of Paint, download Inkscape. It's probably the best free drawing program. I use Adobe Illustrator (AI), which is not free, but you can do about anything with Inkscape that you can with AI. After downloading, go to Help in the menu. You will find an Inkscape manual and some good tutorials. Any of these drawing programs need practice.

https://inkscape.org/en/

 

[FrugalRefiner]

Thanks for the recommendation GSP! I've been needing a new drawing program. This one looks like it should keep me busy learning it for a while.

Dave

 

[goldsilverpro]

Now that you have Inkscape, you might download Gimp (free), which is a pixel manipulation program like Photoshop. I haven't used it but it looks simpler than PS.

http://www.gimp.org/downloads/

 

[FrugalRefiner]

I already have GIMP, thanks. I'm sure I've only scratched the surface of its abilities, but I accomplished what I needed to do. If you want full featured software, you have to be prepared for a steep learning curve. I just started on the Inkscape tutorial.

Thanks again for the recommendations,
Dave

 

[MarcoP]

Yeah GIMP is ok, specially because is cross platform, but at the beginning you'll have some issues even for easy tasks. For example there is not a tool for straight lines, press SHIFT, click and draw but sometimes this is great because you don't have to change tools so often.

 

[Sucho]

Hi guys!

Its a long time ago i wrote something here, but this topic is very interesting for me and corresponds with my ideas.
It touches my field partially, i am working on solid phase extractants based on ionic liquids for heavy and radioactive metal separation.

my pium desiderium is to apply solid phase membranes or liquid surfactant membranes in refining cells.

The key elements for electrolytic cell containing various metals in electrolyte would be the kinetics of sorption/desorption on an membrane - includes surface, hydrophobicity/hydrophilicty of the membrane, in a case of fixed extractants- washing out extracting agents on each site of membrane and selectivity, of course.

The problem would be speciation of desired membrane-transported metal ion on each site of the membrane according to the direction of current in cell.

i am really curious for updates in this topic !