T-Cell Junior Harvest
Entry posted by Swede
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This is going to be the LAST "Harvest" blog I do, because it is getting repetitious. This one is worth detailing a bit because it has gone up to a scale where new and different techniques are required to successfully gather and clean the chlorate crop. It will also show portions of the T-Cell that succeeded, and failed, spectacularly. Subsequent blog entries will deal more with specifics, and with perchlorate conversion. I've got enough KClO3 to feed a perchlorate cell for a long time!
From the last blog, we were left with a circulation failure due to crystal clogging, and the CC vat was set up as a monolithic, stand-alone cell. The run went well, with one exception... EVERY port or hole in this thing was JAMMED with chlorate crystals. These were not soft, fluffy, loose crystals. They were hard, compacted, and a real pain in the ass. I need to rethink many aspects of plumbing this thing. And I think I have them solved, in my mind, at least. Most of the fixes wil make use of larger bore ports and devices.
Tracking the chloride ion concentration, the T-Cell went from 125 g/l to 95 g/l. It could have gone lower, but I was ready to halt the run, as maintenance (due to the jammed ports) was becoming difficult. This was the first run to make real use of pH control in the form of a Hanna dosing pump set up on a timer. Keeping the pH as close to 6.8 makes the cell more efficient, and it also makes the product much easier to handle... less chlorine, and less hypochlorite ion.
Salt creep was a real problem. Despite the Viton gasket, it encrusted the sides of the T-cell vat. I think I can correct this with four more studs, to even out the downward pressure of the lid a bit more.
When the time comes to harvest a cell, it needs to be allowed to cool to ambient or below; otherwise, significant chlorate wil be carried away in the decanted liquor as dissolved salt. It is a bad idea to let the electrodes remain in the liquor without power, so I turned the current down to 1 amp, and waited.. and waited. It wasn't cooling as quickly as I wanted. In the end, I pulled the plug, wheeled it outside, and popped the lid to speed cooling.
I was pleased to see the anode and cathodes were in fine shape. A bit of crystal on the anode, probably due to loss of circulation at times, but nothing bad.
The cathodes were not warped... good deal. The PTFE retainer clips were still in place. Peering into the vat, I was rewarded with the sight of a thick layer of crystals:
Hours went by, and the electrolyte was still too warm. I decided to hurry it up a bit by hanging a big ziploc full of ice in the liquor. This did the trick, and by early afternoon, I was finally ready to decant and scoop.
There were fine crystals suspended in the electrolyte, but I ignored these, and decanted the bulk of the liquor with a plastic food container. All of this liquor went into a poly jug for recycling/replenishment with chloride ion, and reuse in the next run, as this liquor is saturated with potassium chlorate. At 25 degrees C, the 25 liters probably contains 100g per liter of potassium chlorate, or 2.5 kilograms. That's quite a bit!
It was time to gather the crystals. For a batch of this magnitude, forget about paper filters in any form. The best option is some sort of 5 gallon bucket screen, either one of the stainless bucket sieves from the guy who makes them for pyrotechnics, or one of these biodiesel plastic mesh screens, available from Dudadiesel.com These are relatively inexpensive. I chose the 400 micron mesh. He also sells on eBay. It is not the strongest product, but it seemed to hold up very well.
As I scooped and filtered the crystals, I encountered an oddity... there were two very distinct layers in the vat. The one at the bottom was rock-hard and composed of larger crystals. This layer was so hard, it took a bit of hacking with a plastic rod to crack it into manageable pieces. On top of that layer was a softer layer composed of finer crystals. This layering can be seen pretty clearly in this next picture:
The depth of the crystal mass seemed infinite. This is a "satisfactory" harvest! I scooped and scooped; eventually, the filter was almost full. Electrolyte continued to drain into the bucket throughout this process. The chunky masses of crystals easily broke up in my gloved hand. I drained as much clinging liquor as I could by manipulating the mass in the filter. The next step was to add cold, fresh water into the vat to consolidate crystal remnants. This was poured onto the mass to both wash it, and add the chlorate remnants from the vat. The vat was then hosed down while the crystals drained.
Using a gallon jug full of refrigerated water, the crystals were washed and manipulated with a big spoon so as to expose as much of the crystal mass to the washing as I could. All of the water in the bucket, now laden with chlorate, was added to the leftover liquor... waste not, want not.
The final step was a washing with cold 75% water, 25% ethanol. The ethanol inhibits further losses of chlorate, and wets the crystal mass well. This washing was disposed of. I suppose I could boil off the ethanol, but the amount of chlorate stolen by this wash is negligible.
The pan in this picture is about 3 feet long. After drying, the yield was over 4 kilograms! 
Before this thing runs again, I've got a bit of work to do. The sight glass I was so proud of jammed hopelessly with crystals, as did the sample port with a ball valve. I inspected these fittings, and the crystal mass was so thick, and so hard, it looked like epoxy had been poured into them. The system needs to be modified a bit to prevent this. The breaking bubbles from the air pump agitator is also a problem. As well as clogging, when the tubes did work, they were slinging a large amount of spatter onto the viton gasket, resulting in excess salt creep. That too will be fixed, probably with a large-bore vertical standpipe system to deliver air to the bottom of the cell.
I've ordered additional chemicals, and hope to have a PbO2 plating system set up soon. I am ready to move on from chlorate production, and get into perchlorate, which was the goal from the outset.
The MMO mesh performed perfectly, and looks as good as it did at the beginning of the run.
Next up - serious perchlorate production!
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