The Bucket Cell - Start to Finish

[pyrojig]

I suppose we'll go for the gusto and use the type of setup Swede uses;

 

an acid reservoir plus

an accurate digital timer and

a 12Vdc Teflon valve and

a Kynar needle valve to feed acid into

an acid dispersal tube in the bucket

(Wow, what a mouthful!).

 

It should make an excellent pH control system.

 

WSM

This sounds juicy !!!

@ Swede:

Evaporation is kind of a bastard with these setups , especially when it is summer and or the sys flat out runs very hot. WSM suggested a catch for the exhaust tube to filter out any liquids. They can be recycled back into the cell.

[pdfbq]

My exaust hose (garden one) goes first 2 meters up. Its refluxing but probably only in a colder climate.

[WSM]

This sounds juicy !!!

@ Swede:

Evaporation is kind of a bastard with these setups , especially when it is summer and or the sys flat out runs very hot. WSM suggested a catch for the exhaust tube to filter out any liquids. They can be recycled back into the cell.

 

I wish I could take credit for it, but a friend suggested it first. If you run the vent into a one gallon (3.785 liter) glass jar positioned on a shelf above the cell, and vent that jar, it works well as a vapor trap.

 

WSM

Edited October 26, 2012 by WSM

[pdfbq]

If you just put your vent hose straight up for 2 meters you don't need to trap anything.. It is eh .. autotrapping .. I invented that .

[WSM]

If you just put your vent hose straight up for 2 meters you don't need to trap anything.. It is eh .. autotrapping .. I invented that .

 

Interesting! So we have a choice, if we have a tall ceiling where our cell is, we can do it your way. If our overhead space is limited, no problem, we can do it my friend's way.

 

Sounds like a win-win to me.

 

Thanks for sharing your method, pdfbq.

 

WSM

Edited October 26, 2012 by WSM

[pyrojig]

psfbq.

I see one prob with your theory 'if using smaller tubes'. I pulled my opaque tubes above the cell a couple feet, and saw that the waste liquid was trapping and building up in the tubes. this created backpressure that resulted in saltcreep on the cell. The use of a bigger tube will vent off more steam, and a catch jar may be the answer to the prob. > I would rather deal with a bigger exhaust tube than a backpressure issue. Assuming you used a big enough tube, the prob would be non- existent for the style your speaking of( lifting the exhaust tube high above the cell. )

[WSM]

psfbq.

I see one prob with your theory 'if using smaller tubes'. I pulled my opaque tubes above the cell a couple feet, and saw that the waste liquid was trapping and building up in the tubes. this created backpressure that resulted in saltcreep on the cell. The use of a bigger tube will vent off more steam, and a catch jar may be the answer to the prob. > I would rather deal with a bigger exhaust tube than a backpressure issue. Assuming you used a big enough tube, the prob would be non- existent for the style your speaking of( lifting the exhaust tube high above the cell. )

 

Hi pyrojig,

 

It sounds like he's using a piece of garden hose for his exhaust vent. That's brilliant, really (large ID, flexible and readily available everywhere). I never thought of that, but it would work just fine I believe (as long as it's not too long).

 

I did consider using 1/2" or up PVC pipe, but it's not flexible or convenient to use in any longer length.

 

To aid in the "refluxing" of vapors in the hose, you could plumb it through an ice water bucket in warmer weather. Imagine a short length of larger diameter PVC pipe over the outside of your vent hose with chilled water slowly running through it. There I go again, making a simple idea complicated !

 

Good job, pdfbq!

 

WSM

Edited October 26, 2012 by WSM

[pdfbq]

I see one prob with your theory 'if using smaller tubes'....

The use of a bigger tube will vent off more steam, and a catch jar may be the answer to the prob. )

Tnx pyrojig for your reply. Its not a theory though, it just works for me I think. I have a 2 liter NaCl -> NaClO3 cell and run 25 amps and up. It gets way too hot without cooling so I put it in a water bath. I have to add more than a liter of water every day to this water bath to keep the level up, but the liquid level in my cell just drops slowly.

 

I dont think a bigger hose (say size garden hose) will vent off more steam. If your cell is closed airtight the flow will be slower in a bigger hose due to the lower gas pressure in your cell when it rises out.

Edited October 26, 2012 by pdfbq

[Swede]

I do have a question on venting through liquid. The problem I see is that you are definitely adding back pressure to the system, in an amount equal to the height of the water column the exhaust tube is located in. This can be significant.

 

A cell generates its own gas, mostly hydrogen. Most guys use a bubbler setup for stirring, which adds more gas, so I'd be a bit concerned about backing up the vent tube any more, or the salt creep is going to be a problem, unless one has a very well-sealed cell.

[WSM]

I do have a question on venting through liquid. The problem I see is that you are definitely adding back pressure to the system, in an amount equal to the height of the water column the exhaust tube is located in. This can be significant.

A cell generates its own gas, mostly hydrogen. Most guys use a bubbler setup for stirring, which adds more gas, so I'd be a bit concerned about backing up the vent tube any more, or the salt creep is going to be a problem, unless one has a very well-sealed cell.

 

If you mean me, I meant to jacket the exhaust hose (and chill it), not bubble the exhaust through water (though that has merit for trapping corrosive vapors, if done correctly). I agree about the back pressure issue and the salt creep it would encourage .

 

WSM

[WSM]

psfbq.

I see one prob with your theory 'if using smaller tubes'. I pulled my opaque tubes above the cell a couple feet, and saw that the waste liquid was trapping and building up in the tubes. this created backpressure that resulted in saltcreep on the cell. The use of a bigger tube will vent off more steam, and a catch jar may be the answer to the prob. > I would rather deal with a bigger exhaust tube than a backpressure issue. Assuming you used a big enough tube, the prob would be non- existent for the style your speaking of( lifting the exhaust tube high above the cell. )

 

I think he was referring to using a garden hose (and I'm thinking at least 1/2" ID and probably more like 5/8" ID) and running it straight up like a pipe or chimney. I can see if you used a smaller tube and it curled where you had a low spot that filled with condensed liquid and blocked the vent, where you'd get a serious back pressure problem in the cell.

 

I imagine the larger exhaust tube would allow a free flow of any pressure developed within the cell. His mention of refluxing makes sense if operating during the Winter months and the hose is cold.

 

On the other hand, the use of a vapor trap works well to keep salts and corrosive vapors contained where they can be reintroduced back into the cell liquor occasionally.

 

WSM

Edited October 30, 2012 by WSM

[50AE]

Nice project Swede, keep on with the good work!. I also have a "barrel" cell in mind, a HDPE 50L container running on huge current, something about 50A. There will be pH regulation of course and very important - a stirrer. From experience, it's very important to stir the electrolyte, otherwise it looses homogeneity. Potassium chlorate crystals stay down and HCl gets trapped between them. Then, when time comes for extraction, there's a horrible smell of chlorine I guess, because many trapped HCl droplets react with hypochlorite from the electrolyte. I hate the smell and..

 

It also keeps solubility even.

 

As power supply, I will use a MOT, then full rectifier, then a CLC filter.

Edited November 12, 2012 by 50AE

[Swede]

Thanks 50AE, and I agree 100% on the need for circulation. You can get away with it for small cells, say anything 3 or 4 liters or less, but with a larger cell one has to keep the bulk reaction in mind. With something like a 50 liter drum, it's essential.

 

In a proper cell, the chlorate isn't all formed at the anode, it is in fact formed throughout the cell, away from the electrodes. Think of it as the electrodes MAKE the chlorate precursors. If these precursors are not evenly and intimately mixed, efficiency suffers, badly.

 

Guys remember also if using potassium salts, an air pump bubble circulator will jam, guaranteed, as soon as the electrolyte reaches saturation. This can be avoided with a manual stirrer device that doesn't use air, or by having the air reach the bottom through a PVC pipe. I haven't tried the latter, but I'm confident the wide bore will remain open, so long as the bottom of the pipe is at least one third of the way up from the bottom of the cell. The lower third will become solidly packed with crystals towards the end of the run.

 

This thread/project is momentarily stalled, but I've got some vacation time now and I hope to get it running soon.

[pyrojig]

Swede ..

I have run the 5gal BC sys for quite some time, and noticed that much hinges on the shape and placement of the electrodes. Two BC's with diff electrodes gave diff results. I noticed the longer electrodes gave more lift with the gasses , stirring the electrolyte, and keeping the cell hot.

I think some areas need to be further looked into, like the shape and placement of the electrodes and their resulting CE's .

Just a thought to chew on .. .

[WSM]

Swede ..

I have run the 5gal BC sys for quite some time, and noticed that much hinges on the shape and placement of the electrodes. Two BC's with diff electrodes gave diff results. I noticed the longer electrodes gave more lift with the gasses , stirring the electrolyte, and keeping the cell hot.

I think some areas need to be further looked into, like the shape and placement of the electrodes and their resulting CE's .

Just a thought to chew on .. .

 

I have to agree. If your cell is on the tall side, either use electrodes that are long and slender or use compatible leads that reach deeper into the cell to promote hydrogen lift and greater circulation within the cell. Otherwise, some sort of mechanical (propeller or bubbling air) stirring should be added providing you heed Swede's warnings.

 

The main point is to place the electrodes lower into the cell to naturally stir things up as the cell runs.

 

WSM

[Swede]

I like the notion of electrodes down low, but we'd need to watch out for heating with long shanks. I tend to really push things current-wise, so if the current is dialed down, maybe it won't be that much of a problem.

 

I think the ideal solution would be coaxial tubular electrodes that can be adjusted in height. You'd get a really nice and quite potent flow through that system, both from gas generation and thermal motion.

 

One of my cells was a tall acrylic tower, maybe 5" dia by 30" tall. Without circulation, the standard electrode set created a zone at the top near 80 C, while the bottom was ambient. The hot liquor STAYED at the top. So some sort of electrolyte circulation is critical both from a thermal POV, and also to evenly distribute the precursors for the bulk reaction.

[pyrojig]

This adjustable electrode setup is the solution for the prob at hand. I have found that same prob with the top of the cell running hot 60c and the base being warm. It almost acts like a crystallizer where the forming kclo3 drops out of solution here . But as stated the "bulk reaction" and the precursors are not able to do the grunt work the need to the lower half. It ultimately slows the process and C.E. down. Raise-able electrodes will also cure the prob of "salt bridge" ( if you move them in time )

[WSM]

I like the notion of electrodes down low, but we'd need to watch out for heating with long shanks. I tend to really push things current-wise, so if the current is dialed down, maybe it won't be that much of a problem.

I think the ideal solution would be coaxial tubular electrodes that can be adjusted in height. You'd get a really nice and quite potent flow through that system, both from gas generation and thermal motion.

One of my cells was a tall acrylic tower, maybe 5" dia by 30" tall. Without circulation, the standard electrode set created a zone at the top near 80 C, while the bottom was ambient. The hot liquor STAYED at the top. So some sort of electrolyte circulation is critical both from a thermal POV, and also to evenly distribute the precursors for the bulk reaction.

 

I have some materials to do that. I need to prepare them and try this out. The problem is the MMO tube is only coated on the outside so the inside needs to be protected. I suppose I could turn the OD of two 1/2" PVC pipe caps down and press them for a friction fit into the ends of the MMO tube (which is 1" OD). I also suppose I can fill the MMO tube with distilled water so the assembly wouldn't be buoyant.

 

It's just possible that If I leave the ends open, the bare or oxidized CP titanium inside would be just fine, but I'd hate to take that chance with material that cost me $200 per meter (made by DeNora)!

 

Any thoughts?

 

WSM

[WSM]

I have some materials to do that. I need to prepare them and try this out. The problem is the MMO tube is only coated on the outside so the inside needs to be protected. I suppose I could turn the OD of two 1/2" PVC pipe caps down and press them for a friction fit into the ends of the MMO tube (which is 1" OD). I also suppose I can fill the MMO tube with distilled water so the assembly wouldn't be buoyant.

It's just possible that If I leave the ends open, the bare or oxidized CP titanium inside would be just fine, but I'd hate to take that chance with material that cost me $200 per meter (made by DeNora)!

Any thoughts?

WSM

 

I did some furthur thinking about this for a bucket cell and if my calculations are correct, a four inch (+- 100mm) piece of the MMO tube would demand about 24 Amps, maximum.

 

Considering most beginning electrochemists are using computer power supplies (many of which can supply about 30 Amps long term without any undue harm) this can be a viable option for a bucket cell. It also cuts the bulk cost of the tubular anode down to about $25 if purchased through a co-op (not counting the attached tubular titanium lead). Materials and labor would be the greatest expense.

 

I'm sure most would prefer to use the less expensive surplus MMO mesh available occasionally on eBay for much less, and working with flat anodes and cathodes is less trouble for most of us. Still, it makes you think...

 

WSM

[WSM]

Nice project Swede, keep on with the good work!. I also have a "barrel" cell in mind, a HDPE 50L container running on huge current, something about 50A. There will be pH regulation of course and very important - a stirrer. From experience, it's very important to stir the electrolyte, otherwise it looses homogeneity. Potassium chlorate crystals stay down and HCl gets trapped between them. Then, when time comes for extraction, there's a horrible smell of chlorine I guess, because many trapped HCl droplets react with hypochlorite from the electrolyte. I hate the smell and..

It also keeps solubility even.

As power supply, I will use a MOT, then full rectifier, then a CLC filter.

 

I like the description of your power supply. The modified microwave oven transformer sounds like the most labor intensive component. the full-wave diode bridge can either be a discrete item or made by using four high power diodes properly arranged, and lastly the filter for a clean DC output. I've always heard it called a Pi filter (due, probably, to the resemblance of the arrangement of components to the Greek letter Pi).

 

When you build it, why not photograph the process and share it on APC? I believe many here would benefit from such a project and may wish to copy your efforts. I wonder if this discussion belongs in the electronics section?

 

WSM

Edited December 1, 2012 by WSM

[WSM]

Swede ..

I have run the 5gal BC sys for quite some time, and noticed that much hinges on the shape and placement of the electrodes. Two BC's with diff electrodes gave diff results. I noticed the longer electrodes gave more lift with the gasses , stirring the electrolyte, and keeping the cell hot.

I think some areas need to be further looked into, like the shape and placement of the electrodes and their resulting CE's .

Just a thought to chew on .. .

 

Speaking of the BCA and electrodes, I made some progress today (though I bailed on the photo documentation I thought I'd do). I've recently cleaned and prepared the various bits and pieces for my cathode pair and today I spot welded them together.

 

 

 

 

Here the anode and cathode pair are shown completed in various views. To assemble the cathode pair took several steps:

• clamp (with vise grips) and spot weld the cross bars to the cathode plates (made of the same material)
  
• file the weld spots on the inside cathode faces flat
  
• Spot weld the prepared tubular lead to one of the cathode plates
  
• notch the cathode plate where the anode tubular lead is welded on, for clearance
  
• line up and clamp the first pillar between the two cross bars, near the lead end of the electrodes
  
• line up and spot weld the pillar opposite the first
  
• line up and spot weld the other two pillars one at a time
  

It's important to keep everything lined up as you go, especially since things tend to spin and shift as you're spot welding. Next is modifying the PVDF compression fittings by drilling through so the tubular leads can slide through. Next will be drilling and tapping the BCA for the compression fittings to mount the electrodes. After that I'll drill and tap various other holes for the other attachments and accessories.

 

Man, these things are labor intensive...

 

WSM

[pyrojig]

Wow!!!! great job!

Man those are close tolerances. Should be a hot producing setup.

[WSM]

Wow!!!! great job!

Man those are close tolerances. Should be a hot producing setup.

 

I expect so plus generate a decent convection-like current due to hydrogen lift from the cathodes. As you mentioned about long, slim electrodes encouraging more flow in a cell than square electrodes do, I think these will really help. We'll see.

 

Thanks for the words of encouragement.

 

WSM

[WSM]

Wow, what a busy weekend. Pyrojig came down and we worked hard and finished the bucket cell (at least to where he can complete it on his own).

 

 

We drilled and tapped several holes in the BCA (primarily 1/4" and 1/2" NPT) for the various fittings and attachments. Most of the fittings are PVDF or PVC but the vent is 1/2" PP (polypropylene) and should work fine. The electrodes are spaced fairly close and depend on Viton or silicone tubing spacers to keep them secure and prevent shorting them together. I suppose thin strips of 1/8" PVC sheet could be used as an alternative for the tubing spacers.

 

We'll see how pyrojig completes it and puts it through it's paces !!!

 

WSM

Edited February 4, 2013 by WSM

[MrB]

To encourage circulation, putting the electrodes parallel to the bottom might be an idea. Causing a wider stream of bubbles & heated fluids rather then a narrow, more intense stream.

B!