387 replies to this topic

[Valec]

I've been running my cell for 10 KWh now at 5V, using a solution of abou 500g NaCl in about one litre of water. At the beginning it produced some chlorine, but that stopped quickly an at the moment, there is very little chlorine smell.

My calculations with an efficiency of 54% are, that it would need 15KWh for Chlorate and about 20KWh for Perchlorate.

Now I've got two questions:
1) As I don't know the real efficiency, is there an easy way to find out, if the Chloride has been converted to chlorate/perchlorate. How intensive is the ozone smell mentioned, is it clearly noticeable as an indicator for the finished conversion?
2) Concerning pH-Control: As the solution reached a stable pH of about 9, I added some HCl (100ml of <13% acid - I don't know the exact concentration). The acid was added over three days. Upon addition, there was always an intense development of gas and a strong smell (I think Chlorine, but maybe ClO2).
Now the question is: Has the acid been to concentrated, and thus destroyed my chlorate? Or was ist just some chlorine and my chlorate is perfectly well? Did anyone experience this before?
It would be a bit disappointing if I had destroyed the just produced chlorate...

[alany]

I once went a little too far when neutralising a chlorate cell liquor with HCl after the run. The solution turned yellow-orange from all the dissolved ClO2. I quickly added KOH prills and brought the pH back to about 9, the colour faded and I got a good crop of KClO3 out. Dissolved ClO2 reacts quite quickly with hydroxide ions to form Chlorate.

I've noticed the same thing happen at the start of my cell runs when the pH is quite low and lots of Cl and ClO2 is produced, but as Cl is lost and the pH rises the cathodic Hydroxide reacts and the cell grow clear again, the pH stabilising quite alkaline as Cl loss pretty much stops.

If you are going to inject HCl into your cells I'd recommend doing it slowly, deep in the column, with a good rapid mixing action going on at the same time. That should minimise local pH overshooting and ClO2 production, it will also allow any produced by the local low pH to react with hydroxide before being lost from solution. Good mixing in your cells can promote high efficiency and better cooling, if your electrodes are "tall" the gas production can effect pretty good mixing.

[pkhow]

Please correct me if I am wrong. Adding HCl to bring down the PH should be done very slowly with lots of stirring. If at the point where the acid is being delivered to the solution then local low PH will decompose Chlorate to CLO2. If there is a lot of CLO2 some will be dissolved and cause the solution to go a yellow color and most will go of as vapor. If the over all PH of the solution goes well below 7 it should be raised quickly to stop the chlorate decomposing into CLO2. Raising the PH up above 8 should quickly with Hydroxide should reverse this.
Does any one know how critical is it to get the PH down to near neutral before recovering the chlorate?
Also what indicator would be the most accurate for this?

[gilbert pinkston]

i never worried about pH right before i got the chlorate out.........as a matter of fact i did not add any HCl the day of recovery i figured it was better the chlorate be a little high in pH rather than low but it didnt make much difference i dont think because by the time i washed the dichromate out i think the chlorate was neutral
if pH matters in removing chlorate i wonder why?
keep us informed of your progress please
very interesting

[pkhow]

IT seems you are right. I have not used any dichromate as i beleive you only have to use this with graphite anodes. I have processed some of the electrolyte and I am sure after I re-crystalize it the ph won't be far from neutral and as you said better the ph is a little Hi. I was surprised how little it had to be boiled down before what should be chlorate started precipitating out the size of fine sand grains. I did not expect any to crystalize until I cooled the solution and even then I expected larger crystals.
A lot more came out on cooling but still not as crystals.
Do you experience the electrolyte attacking Stainless Steel container`s you use for boiling down?
I do not know if I still have some chloride but it is surposed to be destroyed later in Perchlorate cells if taken that far.
Do you know how concerned you have to be about chloride contamination?

[alany]

I suspect using dichromate with your MMO electrodes might ruin them.

I purchased a cheap stainless 25 litre pot from K-mart, it was rapidly pitted and contaminated some of my first large perc batch (acid wasing recovered it mostly). It seems to have passivated now, but it will still stain fresh electrolyte if I boil it for a long time at either end of the pH scale. I mostly use the pot for boiling down tailings from the recrysalisation cycles and precipitation supernant. I've got a jar full of crystal slurry (largely NaCl) that will one day resaturate a Sodium Chlorate cell.

I tend to use my 2 litre duran beaker for the initial boil and pH adjustment, but it is becoming too small for my uses. I can't afford a larger one at the moment, but a 10 litre would be about the right size, in that I could do kilogram recrystalisation batches.

Chloride contamination of Potassium Perchlorate isn't a big issue. After all the recrysalisation cycles you need to get the Sodium out there is very little Chloride left. Mine after 3 cycles won't precipitate Silver Chloride from Silver Nitrate solution (and it also flame-tests Potassium violet/purple).

Neither have I found it to be a problem with Potassium Chlorate. The solubility difference is large enough to allow easy seperation.

[gilbert pinkston]

i think dichromate is used with platinum also i am sure i read that but it may hurt your annodes be careful electric here the last time i ask was well below ten cents per kWhr so efficiency other than taking more time was not a problem for me i mostly added the dichromate because the literature said to and it MAY give you a rough idea of the pH situation
if you dont have any just melt some KNO3 and add green chromic oxide from a pottery supply store
i used stainless steel to boil my electrolyte and never noticed any erosion
i used to get the fine crystals also kinda like salt but if the crystalization takes place slow you get a mass of squares like rock candy or individual squares about half an inch in across......i put some pix on here a while back of it
i rinsed my NaClO3 with saturated NaCl then water and sometimes recrystalized it all to remove the dichromate before i put it in the PbO2 perchlorate cell some times it still had a faint color of dichromate but that didnt seem to hurt and it always started out smelling like Cl but that went away in an hour or so and didnt seem to be much of a problem then i just kept adding NaClO3 during the run and after a week or so NaClO4 starts to crystalize out and soon if you let the cell cool it becomes almost a solid mass of NaClO4
(a beautiful sight)
what current density do you run on your annodes?

gilbert

[pkhow]

I will have to purchase a large beaker or a Glass Pyrex Pot if they are still available and find one. The stainless steel is good quality but there is enough reaction happening to stain the water, but the crystals look clean. I rinsed them with a little cold water as well so I hope the contamination is not worth worrying about.
The Chlorate that came out slowly when cooled are large Rhombic looking crystals.
My cell current was 30A in 3L of electrolyte but have reduced it to 20A as the temperature was approaching 90deg and at 20A 60deg~70deg. How necessary is it to re-crystalize more than the once if you are going to run it in a Per chlorate cell?

[gilbert pinkston]

i think the most i ever did was wash by vacuum fiter with salt water then a little water and desolve and recrystalize once.....seemed to do ok
just keep adding saturated chlorate solution to the perchlorate cell until perchlorate comes out and vacuum filter the crystals
that way it is easier i think to remove the remaining O3 from the O4 and also i think the effiecency drops off at low O3 levels so it may waste annode life and if you do try to run the cell until all is converted it wont all be coverted and it will be a bigger problem getting the O3 out
i also used persulphate
when the run starts you see alot of H2 at the cathode but no O2 at the annode because that is all going to make perchlorate as the chlorate concentration goes down and effiecency with it drops O2 comes off the annode that is how i could tell it was about done and you can also smell some ozone but i trust my viewers more than my smellers
so you are running 20A
what is your annode area?

[alany]

I finally got around to setting up the 60 A switcher supply I got from a scraped Bay Networks switch. It is currently delivering 56 A into a 3 litre cell. It is pretty damn near boiling it, I've got a fan running over the works to keep the temperature down.

The only real problem I am having is with the riser to aligator clip interface, it is getting hot enough to boil water and melt the lid of the cell where the Ti risers penetrate. The fan is keeping it from melting down completely at least. I also will need to set it up some permanently, at the moment it is just a rather dangerous lash-up on the kitchen bench:

http://nexus.cable.n...90/p0004846.jpg

It only has to hold together for 3 days or so, and I'll have a 1.6 kg yield of Sodium Chlorate. However I don't think I can live without the kitchen bench for that long though.

[Valec]

Is adding persulphate also helpful in making perchlorates directly from sodium chloride? I think persulphate will sensitize chlorate, so if one uses persulphate the perchlorate should be washed very good to remove chlorate/persulphate, shouldn't it?
What are your experiences? I've got some persulphate here, will it have a noticeable effect on the runtime?

[gilbert pinkston]

im going to guess since persulphate is not mentioned much in making chlorates it probably doesnt help much NaF can be added to NaCl for NaClO4
i use dichromate for chlorates and wash it out for PbO2 perchlorate
i never done without dichromate or persulphate so i dont know how much difference they make i just put it in because someone said to

[pkhow]

I am surprised even the fan is keeping it cool as my 3 litre almost boiled at 30amps. I now cell housing 50% Submerged in a 60Ltr tub water with no fan. To be reliable and last many years the connection in a small commercial chlorine cell the 12 mm wide TI risers are mechanically sandwiched against 12mmx 12mm copper strips. This connection is set in Electrical casting epoxy resin that has high heat conductivity . The Ti risers are submerged in the electrolyte up against the epoxy to conduct heat away from the connections. At 60amps the TI strip would be 25mm wide to keep the R down.
My anode is 200mm x 60mm and the recommended current is 10A. In a chlorine cell they last 6~8 Years running very low NaCl and I believe in near saturated running they last up to 20 years.

[Valec]

Ok, so how much persulphate do you add? If it does not sensitize the product, I think it's worth a try. So, does persulphate sensitize chlorate? (I ask because I'm not going to purify the perchlorate; I'm going to use it for waterfalls, where chlorate impurities should not harm.)

Another question: What is the minimum voltage to make perchlorate? I read something about 5-7V should be used, but I also read that 6,4V are minimum to get the reaction going. Will I have success with the 5V of a ATX power supply?

[alany]

I've never needed persulfate or fluoride in my cells. I run them vanilla and they seem to work pretty well. IMO other additives are just more impurities to deal with in the purification process. Unlike commercial producers efficiency isn't a big deal, electricity isn't our biggest cost, our time is, and purification is far more (personally) time consuming than the actual electrolysis which can run unattended.

I'd destroy the Chlorate anyway. I lower the pH to about 2 with HCl and add a little Sodium Bisulfate while boiling. In a few minutes it won't decolourise Indigo Carmine, but even without the testing reagents just lowering the pH and boiling for a few minutes will destroy almost all of the Chlorate. I bring the pH up again and leave it around 8 with NaOH after all the ClO2 has been displaced from the solution by the boiling (otherwise Chlorate would reform to some degree). Once the solution has cooled you can precipitate the Potassium Perchlorate, and begin the recrystalisation cycles needed for high-quality blues (the time consuming part).

If you are just making waterfalls then the gold colouration of stray Sodium might be desirable, I know I have used "1st cycle" perc in A1 Glitter because it is going to be gold anyway. I believe it is Weingart that lists a falls torch composition based on Sodium Perchlorate. Not sure how he kept it dry, but I am sure it would be a pretty, bright gold colour.

The voltage requirement depends greatly on your anodes, their oxygen overpotentional determines how much voltage you will need. Platinum can make Perchlorate from as little as 4 volts. However, you have to be seeing that voltage *across at cell*. If your IR drop in the wiring (and cell electrolyte) is quite high you may find the cell pulls very little current from a supply only a volt or two higher than the drop across the cell. It may work, but only very slowly. Use very thick wiring and it may work well.

Ideally your supply is constant-current changing its voltage to maintain the desired current through the cell. In practice however you can use a constant voltage supply by varying other parameters to get an acceptable current flow. Electrode spacing and area are the easiest to vary, but will also affect efficiency. Resistance can be added in the current loop if your cell is pulling too much current, even by just a length of thinner wire than you'd normally use, but this is lossy and will waste Watts as heat, heat which may cause you problems, like melting things, wire insulation in particular.

Larger cells are pulling currents that can produce enormous local heating if you have poor connections. You can almost weld with the output of my new supply, so a "hot joint" can rapidly start a fire if you aren't careful.