Chlorate Cell - Theory and Starting Point

[Guppzor]

Disclaimer: The information provided here is for reference only! Chlorates are not something to "play around with". If you are not comfortable handling chlorates then this is not for you!

I would like to share my experiences and notes regarding potassium chlorate production from potassium chloride. I have dug out my old note book and have gone through my notes to come up with the following information. The sources for my original work was mainly the good ol' Wouter Visser site backed up with Alan Yates' notes on his experiences.

I will begin with all of the wonderful maths and theory (well, the stuff that applies to this anyway), and I hope to follow it up with an actual run during my time off over the Christmas break. Hopefully I can provide something useful to the forum.

I realise that many people have built and run cells that they are happy with. This is in no way meant to be the "Holy Grail" of chlorate cells! There is a tonne of information and theory not covered here. I am merely providing some information to people who are interested in trying their hand at chlorates but are unsure where to start. A working chlorate cell can be created with a few carbon arc rods, a suitable vessel, a suitable power supply and some elbow grease. It will not be the most efficient design due to the anode material, but it is cheap and quick to get running.

Anyway, on to the maths in the next post!

[Guppzor]

Basic Information

It takes 6mol of electrons to convert 1mol of KCl to 1mol of KClO₃

6mol of electrons = 160.8091AH
1mol of KCl = 74.5513g
1mol of KClO₃ = 122.5495g

74.5513g of KCl will yield 122.5495g of KClO₃ (at 100% efficiency)
1g of KCl will yield 1.6438g of KClO₃
1g of KCl requires 2.1570AH to convert it to KClO₃

Yield Calculations
1) Theoretical Yield [g] = Amount of KCl [g] x 1.6438

It is desirable to leave a percentage of KCl in solution to help reduce anode wear and minimise KClO4 production.
2) Theoretical Yield [g] = Amount of KCl [g] x (1 - KCl to leave [%]) x 1.6438

The amount of KCl in the cell can be calculated using the cell volume and the solubility of KCl. I chose the solubility value at 20^oC (344g per L) for ease of creating the solution.
3) Amount of KCl [g] = Cell Volume [mL] x 0.344

Using 2 & 3
4) Theoretical Yield [g] = Cell Volume [mL] x (1 - KCl to leave [%]) x 0.5655

The actual yield will depend on efficiency of the cell which is affected by variables such as pH, temperature, and cell layout.
5) Cell Yield [g] = Cell Volume [mL] x (1 - KCl to leave [%]) x Cell Efficiency [%] x 0.5655

So now that we know how much KClO₃ will be produced, how long will it take?

Run Time Calculations
It takes 160.8091AH to convert 74.5513g of KCl or 2.1570AH per gram. I am going to switch to images for the equations to keep things neat.

6)


Incorporate cell efficiency and percent KCl to leave in solution
7)


Using 3 & 7
8 )


From VK2ZAY, average maximum cell amps is 2A/100mL. We do want to adjust this as different cell designs may tolerate more current, while others may need to be run “cooler”.
9)


Using 8 & 9
10)


Now we can use 5 and 10 as our starting equations 

Next we well take in to account some recommendations...

[Guppzor]

Starting Cell Recommendations

If we plug in the recommendations from VK2ZAY our equations get simpler.

Recommendations
1. Leave 10% KCl in solution to reduce anode wear and perchlorate production
2. Run cell at a maximum current of 2A per 100mL.

For the time being we will assume that our cell is 100% efficient. Collecting yield data from a number of runs will allow cell efficiency to be calculated for a particular cell design. Once we know the efficiency, we can start playing with run conditions such as pH adjustment and temperature control. Note that the efficiency calculated will not be super accurate as ambient temperature and conditions out of our control will throw the value. As this is not a commercial scale operation, it is not a critical problem.

From 5


From 10


IMPORTANT - THESE EQUATIONS ASSUME THE FOLLOWING:
1. Leave 10% KCl in solution
2. Cell current of 2A per 100mL
3. 344g of KCl per litre of cell volume

Note:
Cell operating current can vary wildly depending on anode type, cell temperature, pH, cell layout, etc. It is recommended that carbon anodes be run at around 36mA per cm² of anode surface area with a cell operating temperature of less than 40^oC. I may touch on this during cell construction, however this is outside of the scope of this thread as I intend for it to be a way to get a cell up and running reasonably easily.

[Guppzor]

That's about it for now. If anyone has any questions or comments, let me know. I will hopefully add more information over the coming weeks and will hopefully get a physical run done as proof of concept.

As stated in the first post, I will be using carbon arc rods as the anode which is not the best material out there. However, these are cheap and any contamination caused by erosion is particulate, meaning that it can be easily filtered out of the end product.

Edit: I have a MMO anode and Ti cathode on the way. I aim to do a run with a carbon anode and a run with the MMO anode for a comparison.

[Guppzor]

I should also mention that the root equations can be easily modified for other chlorate types.

Appropriate Data

Barium Chlorate
BaCl₂ - 208.23g/mol
Ba(ClO₃)₂ - 304.24g/mol
12mol electrons required to convert 1mol BaCl₂ to 1mol Ba(ClO₃)₂
1.5445AH per gram BaCl₂

Calcium Chlorate
CaCl₂ - 110.98g/mol
Ca(ClO₃)₂ - 206.98g/mol
12mol electrons required to convert 1mol CaCl₂ to 1mol Ca(ClO₃)₂
2.8980AH per gram CaCl₂

Sodium Chlorate
NaCl - 58.44g/mol
NaClO₃ - 106.436g/mol
6mol electrons required to convert 1mol NaCl to 1mol NaClO₃
2.7517AH per gram NaCl

Strontium Chlorate
SrCl₂ - 158.52g/mol
Sr(ClO₃)₂ - 254.529g/mol
12mol electrons required to convert 1mol SrCl₂ to 1mol Sr(ClO₃)₂
2.0289AH per gram Sr(ClO₃)₂