Sciencemadness Discussion Board

Calcium Perchlorate

kilowatt - 19-7-2009 at 10:37

Could calcium chloride be run in a chlorate/perchlorate cell in place of sodium or potassium chloride? Calcium perchlorate would be an ideal precursor to ammonium perchlorate since it would easily precipitate calcium sulfate from ammonium sulfate.

Polverone - 19-7-2009 at 12:50

You will need to prevent the buildup of Ca(OH)2 on the cathode. IIRC I have seen a similar procedure described for producing magnesium chlorate or perchlorate and they used a rotating cathode.

Edit: but Mg(OH)2 is less soluble; calcium may not be so great a problem.

I have found on Google Books some account of calcium chloride electrolysis:
Quote:
Electrolysis of Solutions of Calcium Chloride. By H. Bischoff and Fritz Foerster (Zeit Elektrochem., 1898, 4, 464).— Oettel's statement that a better yield of chlorate is obtained in the electrolysis of calcium chloride than in that of potassium chloride is confirmed. Measurements of the gases evolved during the electrolysis give the percentages of the current employed (a) in the formation of hypochlorite, chlorate, and perchlorate, (b) in reducing hypochlorite at the cathode, (c) in decomposing water. When a solution of 74.3 grams of calcium chloride in 500 c.c. of water is electrolysed with 6.7 volts, and current densities of 9.1 amperes per sq. dcm. at the anode and 13 amperes per sq. dcm. at the cathode, 85.7 to 90.4 per cent, of the current yields oxygen compounds of chlorine, mainly chlorate, 1.4 to 2.9 per cent, reduces hypochlorite, and 7.8 to 12.8 per cent, decomposes water. With a solution of 100 grams of potassium chloride +7.5 grams of potash in 500 c.c. of water, the E.M.F. being 4.8 volts and the current densities the same as before, the corresponding values were 50.9 to 61.9, 12 to 19.9 and 20.8 to 29.6. Both solutions were cooled with ice. A solution of barium chloride gave results very similar to those obtained with potassium chloride. The small reduction observed with calcium chloride is probably due to a layer of calcium hydroxide on the cathode which acts as a diaphragm ; the greater part of the calcium hydroxide formed combines with chlorine, but part of it remains undissolved, free hypochlorous acid existing in the solution and volatilising with the gases evolved. Further experiments show that at 20—25° the best yield of chlorate is obtained from solutions containing at least (preferably much more than) 10 per cent of calcium chloride, and with a current density of 10 amperes per sq. dcm. at the anode and at least double that amount at the cathode; the yield is nearly 90 per cent. The deposit of calcium hydroxide on the cathode considerably increases the E.M.F. required; at 50°, however, 4.55 volts suffice, and the yield is but slightly reduced (80 to 87 percent.)


That is with platinum at the anode. It looks like a promising endeavor but you will have to do further research or experimentation to find out about the chlorate -> perchlorate transformation.

[Edited on 7-20-2009 by Polverone]

kilowatt - 20-7-2009 at 08:30

I wonder if an AC cell would increase the chlorate conversion efficiency by preventing Ca(OH)2 buildup and assuring that all the hydroxide can react with chlorine.

dann2 - 31-7-2009 at 15:28

Hello,

I think current reversal every few minutes will stop the buildup of Hydroxide on Cathode but you will need two Pt electrodes. Some info. from long time ago about Chlorate from the Chloride below where two Graphite electrodes were used its any use.
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...


Dann2

kilowatt - 1-8-2009 at 17:02

Hmm, this might be challenging. Lead dioxide will not work because it would be destroyed during the cathode cycles. It is doubtful that platinum would be feasible as they erode too much in perchlorate cells. Carbon would be a joke in a perchlorate cell. Is there virtually no material which would hold up to this process using the current reversal?

Removing lead dioxide anodes alternately and washing them in acetic acid to remove the calcium hydroxide might be the only feasible method, but would inevitably result in some lead being dissolved. If the calcium was not recycled into the bath, chloride ions would continue to build up until the cell was quite acidic. This could alleviate the calcium hydroxide buildup, but according to the reading would not lend well to the efficiency of the cell and would result in chlorine emission. It would be possible to return the calcium to the cell if acetate were used, because it is readily decomposed (to acetone for what it's worth; this would be a poor route to useful quantities of acetone) at a low temperature. This would be a very time consuming process having to do all that.

[Edited on 2-8-2009 by kilowatt]