Chlorate production continues. While I am mentally preparing for the next step (perchlorates), I simply can't let a good cell sit there and be idle. Get to work, damn you!

I feel that I have a fairly good grasp of producing KClO₃ at this point. I went through many of the typical noob pitfalls, especially underestimating just how harsh a cell environment really is. I've learned how to process used electrolyte to maximum advantage... how to identify the end point, how to purify crystals that are already very clean. Along the way I've also done significant logging, and today I want to learn just how efficient my cell really is.

I don't want this blog to become repetitious. "Wow, here's my new batch. Whoo hoo!" I want to try and at least introduce something new with each entry. Rather than show more pics of fat crystals, I'll show what I did differently this time.

The first step was to eliminate the damned coffee filters. A lot of time and effort is wasted with those stupid things, and unless your batch is 50 grams or less, there is a better way.

Take a large plastic food container. We are going to turn it into a strainer. The crystals that form in the cell are predominantly large, so by drilling about a million small holes in the bottom of the storage container, we can turn it into an effective filtering, and importantly, a washing device.

This container used to be a cell. It's hard to tell from the photos, but the surface is severly clouded and rough, and the plasticizers have been stripped. Lock & Lock, not good. The holes are 1/16", and simply randomly spaced all over the bottom.

I need to drop back into past tense for this report. I tend to mix past and present tense when writing, and it is very distracting. Besides, to get my dream job in a major chemistry lab as head pyro and manager of chlorates, I'll need to write properly!

First, the clear electrolyte was decanted into the recovery bin, which is layered with raw KCl salt. There, over time, and with a bit of agitation, it will take up adequate chloride ions for the next run, as verified experimentally perhaps a week ago. Boiling is not necessary. The raw crystals were dumped into the container, with a thick clump being a bit reluctant...

The acrylic tower was upside down, and the crystal mass was sloowly sliding down the tube. At the bottom, it broke into smaller clumps and fell into the strainer. The strainer bottom was placed on a support to keep it off of the bottom of the tray, so as to allow drainage.

Ice cold water + ethanol was introduced into the tower, swirled, and the slurry was added to the main crystal mass in the strainer. Further washing consisted of additional cold water + ethanol, and concluded with pure ethanol, which speeds drying of the crop. A plastic tray did duty as a drying bin. Placed in an arid room, a fan was positioned to speed drying.

Now, on to the fun part, the analysis of the run! This was the first batch where I truly logged current vs. time, carefully tracking how much electricity was used. The yield for this run was 1,075 grams, but it is not quite dry yet, so for purposes of the remainder of this entry, I am going to assume it is 1,000 grams. The big question, how efficient is my cell? And how much is it costing me? I feel that I have optimized this particular cell. I added another cathode, so as to eliminate extreme heating at the cathode junction. A PTFE tube is routed to the bottom of the cell, and with an aquarium air pump providing power, it bubbles vigorously. The bubbles do an excellent job of stirring the electrolyte, with the primary goal of keeping the solution saturated with dissolved chlorine gas. This in turn keeps the pH at a happy location, slightly acidic. The temperature of the cell is moderated with a bin full of water, and probably averages about 50 degrees C. About the only parameter I did not track was the pH. When I topped the cell, I did so with an acidified KCl solution, as I've noticed my cells tend to go basic if unattended.

My yield: The molecular weight of KClO₃ is 122.6 g/m, thus, 1,000 grams of KClO₃ is 8.157 moles, meaning 8.157 moles of KCl was electrolyzed into KClO₃ salt.

A cell working at 100% efficiency performs like this:

Cl- ----- (160.8 AH) ----> ClO₃-

where 160.8 amperes for 1 hour will convert 1 mole of chloride ion into 1 mole of chlorate ion.

The log revealed I had delivered 2,129.0 ampere-hours to this cell, averaging perhaps 40 amps for the majority of the run. Therefore, my cell required 2129 / 8.157 = 261.00 ampere-hours per mole.

Calculating the efficiency: (160.8 / E_m ) * 100 = 261.00 where E_m is my efficiency, yields 61.7% This is not a bad value for a homemade cell, and the actual efficiency is a bit higher, as some KClO₃ salt is invariably not recovered.

Calculating the cost: Commercial factories plan on 4.5 to 5.5 kilowatt-hours per kg of salt. My average voltage was perhaps 5.50, and converting the power used to kilowatt-hours:

Amp hours X Voltage = Watt-hours

2129 X 5.50 = 11,709 watt-hours, or 11.7 kw-h.

At 12 cents per kw-h, the electricity costed $1.40, probably a bit more due to losses. The KCl salt is 25 cents per pound, or 55 cents per kilo. This converts to 4.1 cents per mole. Since I made 8.157 moles of chlorate, cost for the salt for this batch was 33.5 cents.

Drum Roll Please.... $1.50 + $0.335 = $1.84 per kilo, or 83 cents per pound.

Of course I refuse to factor in the $$ spent on sundries, cells, cables, etc etc. That takes the fun away. It probably costs the major manufacturers about 35 cents or less per pound of KClO₃ salt. Keep that in mind when you are getting gouged at $5 / lb and more for KClO₃!

Conclusion - once set up, a good cell can produce KClO₃ salt pretty cheaply. Any efficiency greater than 40% for a homemade cell is doing well. Oh yes, the pH at the end of the run, after boiling off the hypochlorite, was slightly acidic, just where it was supposed to be!

Much thanks must go to Wouter Visser, from whom I unashamedly stole much of the pertinent data to make these calculations. Wouter's pages on chlorates and perchlorates I believe to be the finest on the internet for technical clarity and accuracy. Thanks Wouter!