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Author: Subject: Best overall chlorine generator?
blogfast25
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[*] posted on 30-9-2008 at 09:28
Best overall chlorine generator?


I'm looking into building a chlorine generator for the purpose of some basic chlorinations and couldn't find any relevant thread here (using search) on a practical homemade apparatus.

The options are of course well known: electrolysis or chemical oxidation of chloride (-I) to chlorine (0) with oxidisers like MnO2, KMnO4, K2Cr2O7, NaOCl etc.

Has anybody here some experience with a generator capable of making mol quantities of Cl<sub>2</sub>, in a way that output is fairly easy to regulate, even stop altogether when needed? Safely?
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[*] posted on 30-9-2008 at 09:47


http://www.sciencemadness.org/talk/viewthread.php?tid=9713

;)
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woelen
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[*] posted on 30-9-2008 at 09:49


A good option is to use a Kipp's apparatus, combined with coarsely crunched tablets of TCCA and dilute HCl. The Kipp's apparatus allows regulation of the flow of gas and even stopping the production of gas. A Kipp's apparatus is fairly expensive though, EUR 100 is a reasonable price for a suitable one. But it can be reused at any time, and gas production can be shutdown or continued at any time.

Cleaning of the gas before use can be done by bubbling through water for removing HCl-vapor and then passing through a tube, filled with anhydrous CaCl2 to get rid of water vapor.




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blogfast25
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[*] posted on 30-9-2008 at 11:26


Wow. Interesting thread on TCCA (Trichloroisocyanuric acid C3N3O3Cl3) Cl2 generation. So that's an OTC material, huh? Also interesting because for my purpose oxygen should be kept low, if at all possible...

Any best places to buy small quantities of TCCA?

[Edited on 30-9-2008 by blogfast25]
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[*] posted on 30-9-2008 at 11:58


Any swimming pool place should sell em as chlorine tablets... make sure u read the packed tho so u know what ur getting.
Ebay may sell some but there are loads of online pool suppliers but the problem is there are like 5 sorts of pool chlorine tablets so its risky as to whether u will get the right one.
And the final product, cyanuric acid is usefull too! ( i think lol)
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[*] posted on 30-9-2008 at 11:59


A kipp's apparatus works with things like FeS and Zn with acid because the FeS and Zn are not soluble. what stops the acid dissolving the TCCA and reacting "forever"?
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[*] posted on 30-9-2008 at 12:31


That's why I wrote to use crunched tablets. These pieces of TCCA are very hard and do not dissolve easily. Just try adding the stuff to water, it only dissolves VERY slowly. If you add the material to acid, then chlorine is produced and the piece of TCCA slowly is eaten away from the outside. As soon as you close the Kipp's apparatus, chlorine production will lead to driving the acid below the chunks of TCCA and chlorine production soon will stop.

Btw, I am working on a kind of replacement for a Kipp's apparatus, based on a gas wash bottle, a separation funnel and some tubing. I hope to write a webpage about this soon, but there still are some minor issues, especially when the flow of gas is going fast.

[Edited on 30-9-08 by woelen]




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blogfast25
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[*] posted on 1-10-2008 at 06:58


Yeah, loads of "chlorine tablets" on eBay but predictably no one lists whether it's TCCA or Ca hypochlorite (or other). Best ask before buying (info should be on the label I guess).
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[*] posted on 6-10-2008 at 15:17


Quote:
Originally posted by blogfast25
The options are of course well known: electrolysis or (...)


The electrolysis of saturated brine (NaCl solution) is a cheap and dirty way to generate chlorine. My major complaint is about how the collection of the gas evolved at the electrodes is usually done, by bubbling it into overhead tubes filed with the electrolyte. Not only is this an unnervingly small size batch process; its disadvantages are evident when one intends to use the generated gas in a successive reaction.

One way out would be to use a huge (stoppered) syringe instead of common test tubes or graduated cylinders and immediately close it when full of gas.

Another solution would be to lead the gas directly into the next reaction flask (usually by bubbling), which requires a positive overpressure at the anode. From practical experience I know it's not enough to fit a pipe over the anode, as the bubbler would provide enough counterpressure for the gas push the electrolyte out of its half-cell and go to waste. The following design remedies this issue: the anodic and cathodic half-cells lie in distinct 3-necked flasks (alternatively, a simpler analogous device can easily be assembled), which are connected by some simple tubing filled with electrolyte (no membrane, cotton plugs, etc) equalizing the pressure. Clearly the fittings must be airtight to avoid dissipation. As long as the exit tubes (top necks) admit a reasonable flow of gas, gravity ensures that no matter how strongly the gases are generated, each will remain in its native flask and can be led out through the top neck.

Chlorine (or hydrogen) produced this way is pretty wet (depending on the working temperature during electrolysis; boiling is common with strong currents) and dirty with oxygen (especially if the electrolyte is too dilute and the voltage too high) and aerosol. Similarly for the hydrogen. Both gases can be dried and cleand the usual way before use.

Although no continuous process (the electrolyte has to be refreshed from time to time), this setup provides much larger batches and long, uniform generation of chlorine (etc).

ChlorineBrine.jpg - 6kB
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[*] posted on 7-10-2008 at 07:17


Yeah the TCCA method is unbeatable. I have used it for producing many many moles of Cl2. If you don't feel like shelling out the cash for a Kipps, a standard 600ml erlenmeyer flask with dropping funnel and outlet tube affixed works just wonderful. If you go with this method, powder the TCCA moderately finely (shoot for coarse sand) and mix with a small amount of distilled water. A stirrer would make this even more friendly, but even without it is a very steady stream of quite clean Cl2 gas. The premixing of water is quite important, otherwise the HCl will tend to clump a portion of the unused TCCA up, making it useless. Remember that 1 mol of TCCA (230g) and 1 mole of 31% HCl (~120ml) will generate 3mol of Cl2 gas. Simply wonderful I must say.



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[*] posted on 7-10-2008 at 08:51


That would be 3 moles of HCl, no?



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[*] posted on 7-10-2008 at 09:37


Yes, 3 mol of HCl is needed for 3 mol of Cl2.

I have done many different tests with all kinds of chlorine generators and the TCCA method gives best results. The chlorine from electrolysis contains quite some oxygen (can be shown by bubbling the gas through NaOH-solution and collecting the gas which does not dissolve). The gas from calciumhypochlorite contains quite some CO2 as well, due to contamination with CaCO3. Besides that, there still can be some O2 in this chlorine as well.
HCl + KMnO4 also gives a nice steady stream of pure Cl2, but the price of KMnO4 is too high to make this economical.




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[*] posted on 7-10-2008 at 13:08


I am always getting confused on the nomenclature of the trichlorocyanurics. This is not TCT is it?



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[*] posted on 7-10-2008 at 17:32


To death with non-IUPAC acronyms :P

TCT refers to cyanuric chloride (not to be confused with cyanogen chloride), a compound of C and N alone.

TCCA (TCCS on the german forum) stands for trichloroisocyanuric acid, with a similar structure. This also contains oxygen.

Note the different attachment of the chlorine. The chemical properties are thus quite different. The first is more interesting to have (for syntheses etc.), while the second is more OTC (generation of chlorine, maybe oxidations, but not much else as far as I know).

[Edited on 7-10-2008 by jarynth]
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