The Bucket Cell Adapter (BCA)

[patsroom]

Hello Swede,

I am testing the dilution of fluids now. I am using vineagar/water as the HCL and tap water is being introduced by a plastic bottle.

I stared a new topic and called it Lets' Take this Outside so the discussion would not cross over your Cell Adapter. The topic was not well well recieved because of a few issues but we will see if if makes it.......

Pat

[Arthur]

Assuming that your HCl dosing pump is timer controlled, could you manually adjust the off time say by +5% each day at a fixed time.

 

If there was computer logging continuously then could the PC control the duty cycle of the pump with the off time dependant on the amphours passed.

 

Take a HCl tank on one level with two chambers divided by a panel with a small hole say 1mm or sub .625"

If the two chambers are filled with 50% and 40% HCl and the draw off is in the high side, then each time you remove a ml from the high conc side half a ml of the less strong comes through to weaken the solution a little.

 

Added

If you can cut the taper, then make the dividing wall thick enough to take a burette stopcock, then you can fill the two containers easily.

 

Either way, control of the acid addition taper would be the ratio of the two chambers volume and concentrations.

Edited December 6, 2009 by Arthur

[patsroom]

Hello Swede, I hope that you can help me as it seems that a few things when right over my head. The Questions I have are:

1) How much HCI fluid did you add every two hours in ml. I know that you started with 550 ml of 16% that you used to subtract from over the course of running the cell.

2) How long did you run the cell for in hrs.

I am sorry that I lost track, but if you can help I would be thankful for you reply.........Pat

Edited December 6, 2009 by patsroom

[Swede]

The cell ran for 4300 amp-hours, and except for a very short time at the beginning and end, it was at exactly 40 amps, so ignoring the variations, it ran for 107.5 hours, or 4.48 days, yielding approximately 3 kilograms, wet and dry, from 8.7 liters of electrolyte.

 

16% HCl additions were added every two hours.

 

Total 16% HCl consumed: 550 ml

Number of doses (1 dose every 2 hours): 53.5

16% HCl per dose: 10.28 ml

 

If you use typical hardware store concentrated HCl which is 32%, it would take 5.19 ml every two hours when running at 40 amps.

 

Remember the rule of thumb is: 0.114 ml 16% HCl per amp, per hour, or 0.057 ml of 32% acid per amp, per hour.

 

Over two hours, I would have delivered 80 amp-hours of electricity to the cell.

 

Theoretical acid usage: 80 aH * 0.114 ml = 9.12 ml acid every two hours

My acid usage was 10.28 ml every 2 hours, a bit high, and it showed with the pH being a tad low, especially towards the end of the run.

 

Diluting the concentrated acid does two things - it makes it a bit easier for the equipment (pump, tubing, cell) to handle, and it makes accurate delivery a bit easier, as the volume is larger.

[Swede]

Arthur, I agree that in the future, it might be easier to simply manually adjust the timer for acid delivery, but it's fun to contemplate designs that do the job for you. A computer would be ideal... I like the notion of a divided vat as well. The DATAQ software has an SDK, and it would be possible to make a dedicated system (probably using Visual Basic, as I am not up on C+) that would be devoted to this particular process. The DATAQ hardware has a pair of outputs that could easily be used to control any hardware desired. Definitely food for thought.

 

Here is a post I made at Science Madness today: I'm ready to power up the lead dioxide anode made last January for the first time...

 

The small test cell is completed. I didn't realize initially how small my LD anode really is. It measures 8.9 X 4.6 cm, with a basic surface area of 0.41 dm^2. Given the convolutions, the surface as viewed under a microscope, and the mesh configuration, I am taking a wild guess and multiplying this by 2.4 to determine the functional surface area. A major MMO manufacturer told me that their MMO mesh was 2.2 times the basic dimensions.

 

This yields a surface area of 98.4 cm^2 or 0.984 dm^2. I'm going to call it 1.0 dm^2 for purposes of current. Literature yields a range of 15 to 35 amps per dm^2, and my thoughts are 20 amps is a good starting point, which can be altered depending upon temperature, with 60 degrees being an upper limit. The fairly small Ti strap is going to limit the current anyhow - this anode was made when my understanding of the limitations of titanium as a conductor was not as good as it is now, and the strap is too small.

 

The cathode is titanium, and fairly small, yielding a higher current density at the cathode. For the first run, at least, I am not going to add NaF or any other sort of additive. I want to see what sort of CE I can get in the native state.

 

The only other change I made was the use of viton gasket rather than skived PTFE gasket, with the hope that it will reduce the inevitable salt creep.

 

Tomorrow, I will mix up the chlorate and power it up.

 

http://www.5bears.com/ld1/ldbca001.jpg

 

http://www.5bears.com/ld1/ldbca002.jpg

[Arthur]

Whatt is the cost of the dosing pump setup? Could you have four dosing pumps and dose 16% HCl on the first day, 15% on the second, 14% on the third etc

 

Could you have a second dosing pump and add say 50ml of water to the acid at each midnight so that the acid dosing the cell is reduced daily in concentration.

[patsroom]

Thank You for the reply. And the test tank looks good. Can hardly wait for the end results.

[Swede]

I think for the next major run, I am going to go with a gravity system. On eBay, I found a 12V PTFE solenoid valve, so all I have to do is plug in a 12VDC wall transformer into the timer so as to turn the solenoid on and off. The difficulty with the pump lies in cavitation and air in the lines. What seems to happen is that due to positive pressure in the cell, gases tend to creep up the acid delivery line, creating an air gap in the line. The next time the pump comes on, it re-delivers the gases first, then the acid begins to flow. This makes it hard to be consistent and accurate.

 

A gravity system eliminates the pump entirely, which is typically a $150 item vs a $15 solenoid valve. The high positive pressure in the line should keep the gases out, and if the reservoir is high enough, head pressure variations as the vat level drops will be small, as a % of total delivery. The only "gotcha" - gravity-feed hardware needs to be well-made and immune to HCl, because if a leak develops, you are going to drain a liter or more of strong acid where it doesn't belong.

 

The chlorine gas that accumulated in the acid delivery line of the bucket cell destroyed about 25 cm of good Tygon tube.

 

One last observation - the HDPE as used in the bucket cell definitely degraded. The area above the anode, which is hit with a Cl2 gas stream on a continuous basis, has a texture about like 120 grit sandpaper. Additionally, it is a bit soft in that area. Chlorine is just a killer, materials-wise. A typical HDPE hardware store bucket is going to last maybe 4 to 8 runs, I'm guessing, before a new bucket or lid is needed. But still, the concept is sound. Buckets are cheap compared to a fabricated tank.

 

http://www.5bears.com/ld1/ldbca003.jpg

Edited December 8, 2009 by Swede

[bikemaster]

Chlorine gaz is the bigest ennemie in chlorate cell... My pestiglass bucket cell adapteur (much more basic that yours) was eat (like burn) over the anode too. The corrosion stop when the coating of salt start. The coating of KCl was giving a small protection, but with an cell with no pH control, the amout of Chlorine realease is much lower. I don't know if it will make a good protective coating on plastic, but will it be possible to put a good coating of fluorocarbone paint on the ,let say polypropylene, to protect it from chlorine gaz?

 

For the gravity systheme, that make a lot of time that i am working on something like this. Four month ago a was sure that i got the right way to make it, but Swede came with the fact that the HCl need change with the chloride concentration... That don't broke all the concept, but I need to revisit it...Any way i like this,this is the nice world of chemistry !

 

After to have have see the attachement:

 

Adventage:

- Low cost (compare to dosing pump)

- The pipette will protect the tubing over it from Cl gaz and it will give a slower droping rate of the HCl

- The vent tube will prevent the chlorine to stay there

- The systheme will drop a pready accurate amount of solution (more precise that timed pipette over time)

 

desaventage:

- 2-3 foots structure over the cell

- Need a special timer (like DAQ) too fallow the need of HCl

- maybe others...it always have others

Sans_titre.bmp

[tentacles]

It might be possible to use a gravity feed system with a tall column (so the level changes fairly rapidly) and a restriction on the outlet. The lower the level falls, the less comes out in a given time period.

[bikemaster]

The probleme is that we are limited to 1/4 tubing (can't easily have smaller). So if the column is too long, they will have a lot of HCl by addition and that will make the pH to vary a lot. But if we make some test and that the volume of HCl is not too big, that will be a good systheme.

 

The first snow tempest will fall tomorrow expecting to see the same thing in texas, all of it concentrate in a PERchlorate cell. Good luck Swede!

 

 

 

Someone know where is my snowboard ...

[Swede]

From Science Madness - the perc cell is at 24 hours....

 

Report, day 2: Good news - Perchlorate is accumulating. Bad news - about 5 of the bulbous nodules on one side have fallen off the anode. Damn. I'm wondering if I didn't sabotage myself with too high a voltage and not enough cathode area.

 

The edges of the underlying MMO anode were bare titanium due to saw-cutting of the original MMO material. If there is a consistent degradation of the LD over bare Ti, but good adhesion on the MMO, then that would be a good clue.

 

I have dialed the amperage down to 12 amps to reduce the voltage.

 

I am disappointed, but the bulk of the anode is soldiering on, it is just about 5 separate warts that have parted company... but that is a bad sign that the overall anode integrity is not as strong as I'd hoped.

 

Thoughts - A cylindrical form for the LD would probably produce fewer weak areas for this sort of failure. Surrounded by a larger tubular cathode, you'd have a very even current distribution, and perhaps less erosion, but then you're back to the original problem of plating bare titanium, unless you can obtain a cylindrical MMO anode to plate.

 

It's probably time to break out the plating rig again... argh, I hate plating LD, it gives me the creeps. But this time, I'll not stop with just one, which was stupid. While the bath and rig are set up, it'd be best to plate several different forms if the bath can support it.

 

I don't want to overemphasize failure, it's just 4 or 5 edge warts, but I was hoping it would come through without any mechanical failure at all.

 

Another problem - the mesh holes in the LD are PACKED with crystalline perchlorate, and the surface of the anode is dusted with it. I attempted to position the bubbler to kick these crystals off... we'll see. It may be physically difficult to make potassium (as opposed to Na) perchlorate directly with LD.

 

Sodium would not have this particular issue. I don't know what effect it (the coating/dusting) might have, but it can't be good. If the coated areas of the anode no longer conduct, then the efficiency will slowly drop to nil. On the other hand, what might be happening is that the perc forms on the surface, builds to a certain mass, then drops off, exposing LD for additional conversion. The dusting of perc at the bottom of the tank would indicate that there is a successful conversion.

 

We'll see.

 

I ran this particular cell earlier with a Pt anode and it performed brilliantly, executing a nice conversion to perchlorate. I am not going to give up on LD, but for the casual hobbyist who simply wants to make perchlorate, Pt is hard to beat. Just expensive.

[Swede]

More thoughts:

 

I'm already thinking about a new form of anode that should avoid edge erosion issues. Take a look at this picture from Titan:

 

http://www.titanindia.com/images/lead%20dioxide%20metal%20anode/lead%20dioxide%20graphite%20anode.jpg

 

Note that the periphery of the anode has a strip formed around it. Picture a primarily MMO substrate with strips of CP titanium welded onto it to form a sort of frame. In a LD bath, if the anode is rotated, you are going to get some LD deposition on the framing strip, but it probably will not adhere well at all, as the Ti oxides would form almost instantly. After removal from the LD plating bath, the frame is intentionally scraped clean of all LD. What you end up with is a solid, well-secured, conductive LD mass within the frame, supported structurally by the MMO and the surrounding frame, hopefully keeping edge erosion to a minimum.

[gordohigh]

Not sure if this would apply here but I would think so, In chlorine production cells, the polarity must be reversed occasionally to cause the cells to drop the precipitate, (calcium carbonate) off of them. Also, They use multiple plates all connected on one end for the cathode with the anode plate in the center. Just a FYI. There must be a formula for the sq. inches of surface area between anode and cathode for max efficiency I would guess but I don't know what that would be

 

One more thing, a company called Stenner makes all sorts of timed slurrey feeders designed for harsh chemicals that can be set at a broad range of variables and feed thru a 1/4 in poly tube using a squeeze method. I have access to those wholesale if you thought it might be something you could use.

 

Very interesting stuff you're doing here anyway, good luck.

[Swede]

Thanks Gordo... we can never have too may (per)chlorate geeks hanging about.