Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1    3    5  ..  17
Author: Subject: Permanganates
DerAlte
International Hazard
*****




Posts: 779
Registered: 14-5-2007
Location: Erehwon
Member Is Offline

Mood: Disgusted

[*] posted on 17-6-2007 at 22:02


You need the KOH for sure. Conc. to induce the KMnO4 to precipitate off the anode (common ion effect) But just suspending the particles - I suppose the OH- ions near the anode might just get them. As for graphite, does H2SO4 make a mess of them or only when it's really concentrated? PbO2 seems to have a cult following, 12AX7. Unike most, I have made perchlorate sucessfuly with even graphite. You just have to tolerate the anode erosion and clean up the mess. If it's inefficient, what does it matter? Carbon and electricity are cheap compared with the prices one sees chaged, if you can get it al all.

Der Alte
View user's profile View All Posts By User
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 18-6-2007 at 13:41


I believe graphite forms an oxide (intercalated or something) when subject to anodic conditions. As I recall, it works with any sulfate, and probably nitrate as well. Seems to me the only way you can possibly get perchlorate with graphite is by cheating the reaction with high voltage and current density pushing past the erosion regardless.

Speaking of graphite oxide, a lot of times I've had the graphite sludge from my chlorate cell rise to the top due to adherent oxygen. Now, I would ordinarily attribute this to hypochlorite decomposing slowly, but that only works when the smell of chlorine is strong. Sometimes it happens to low-hypochlorite solutions. Graphite oxide as the erosion product, with a high oxidation potential (above chlorate, but below perchlorate, persulfate, etc.), would seem to make sense, and if it's decomposing in suspension, that would explain the adherent oxygen bubbles.

Anyway, applying to this thread, you have to determine if the oxidation of whatever mechanism operates -- direct oxidation of manganite, production of intermediate peroxide or superoxide, etc. -- if it's lower than graphite's erosion potential.

Tim




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
DerAlte
International Hazard
*****




Posts: 779
Registered: 14-5-2007
Location: Erehwon
Member Is Offline

Mood: Disgusted

[*] posted on 18-6-2007 at 21:19


12AX7, both boiling nitric acid and I think I read somewhere, permanganates, will oxidize carbon to mellitic acid, which is benzenehexacarboxylic acid - I'd draw it if I knew how to in this format. The anhydride of this is mellitic anhydride, C12O9, another weird 'oxide' of carbon.

Sure, you use a high voltage and high current density to make the perchlorate. The rods get eaten away like there's no tomorrow! To make the chlorate, it's essential to make sure anode and cathode products mix - the action is chemical as well as electrolytic; for the perchlorate, this is not as essential although hypochlorite, still produced, is capable of converting chlorate to perchlorate. I use different electrode configurations (Fe cathode). Carbon is the sacrificial lamb. Current efficiency be damned! You are spending more effort to make your PbO2 anodes than it's worth (but I'd love to try one - or Pt!)

With regard to permanganates, I'm working on it (still!)

Regards,

DerAlte
View user's profile View All Posts By User
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 19-6-2007 at 16:10


Mellitic acid is interesting stuff. I bet its first proton or two is strongly acidic (much as EDTA's first has a pKa in the unity range). And yes, not to mention the anhydride being an aromatic oxide. Apparently it occurs naturally as the aluminum salt (mellite).

But I digress... maybe titanium doped with sun-dried shyte would work as an anode. :P (Hey, don't poo-poo this idea -- excrement contains trace elements!)

Tim




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
ciscosdad
Hazard to Self
**




Posts: 76
Registered: 6-2-2007
Member Is Offline

Mood: Curious

[*] posted on 19-6-2007 at 17:33


Patent 3652417 (US) is interesting reading.
It refers to Alkaline Permanganate solutions used for descaling. It uses anionic surfactants to decrease the self destruction of the KMnO4 (as I understand it). It may be applicable to synthesis if it shifts the equbilibrium appreciably.

I have found the boiling point of KOH 40% to be ~132 degC. Has anyone seen a table / graph for higher concentrations? I'm thinking of aerated digestion of KOH and I expect the temp will need to be significantly over 132 DegC.
Perhaps a Eutectic mix of KOH/NaOH?

More searching.
View user's profile View All Posts By User
ciscosdad
Hazard to Self
**




Posts: 76
Registered: 6-2-2007
Member Is Offline

Mood: Curious

[*] posted on 19-6-2007 at 18:38


More searching has turned up Patent No 7 056 424 (US)
This refers to the manufacture of MnO2 electrodes on a stainless steel substrate by initially applying a porous non conducting layer, which may be a fabric, or some deposited porous ceramic or plastic.
What about a porous pot filled with Mercury! I love Mercury.:P
It might make the Electrochemical method a lot more appealing. The key to the method appears to be the electrodes.

I wish they would not use the convoluted legalise in these
things. Just getting my head around the chemistry is bad
enough:(

Patent No 3986 941 (US)

The process is for the electrolytic production of KMnO4 directly from a KOH and MnO2 slurry. (or NaMnO4)
Electrodes can be Stainless Steel (amongst other things)!

20%KOH (aq) at 80 - 90 Deg C. Much more friendly than the process I was thinking of.
Process time is less than a day assuming reasonable currents.

The patent even describes a run using a glass 1 litre beaker :D

[Edited on 20-6-2007 by ciscosdad]
View user's profile View All Posts By User
DerAlte
International Hazard
*****




Posts: 779
Registered: 14-5-2007
Location: Erehwon
Member Is Offline

Mood: Disgusted

[*] posted on 20-6-2007 at 08:23


12AX7, your anode ideas, although a shade far fetched, may indeed have merit! Is not PBO2 a pleasing velvety brown color? But, I fear, sun-baked shyte may have poor conduction characteristics. Liberal addition of titanium powder may help this. I am sure its oxygen overvoltage is suitably high!

Talking of sun-baked shyte reminds me of the layer of crud on the bottom of my graphite perchlorate cells – but there it is the pulverized remains of many a carbon rod that gave it’s life for the cause…

Ciscosdad, nice thinking and research. Damn, before this thread dies of inanition, we’ll have a method, by hook or by crook. A clever and persistent chemist can do anything… Sorry no data on KOH or NaOH/KOH mixtures

When I have time I’ll report on my latest effort and suggest a few ideas – at present I’m midway through testing…

Regards,

DerAlte
View user's profile View All Posts By User
ciscosdad
Hazard to Self
**




Posts: 76
Registered: 6-2-2007
Member Is Offline

Mood: Curious

[*] posted on 20-6-2007 at 15:47


For those of you interested, the Patent Search site I'm using is:

http://patft.uspto.gov/netahtml/PTO/search-adv.htm

The patent Number I'm currently obsessing about is 3 986 941.

As I read it, the procedure can be:
In a (say) 2 litre steel container....
Make a slurry of MnO2 in 20% KOH solution so that there is 4.2 moles of KOH per Mole of MnO2. Add a catalytic quantity of KMnO4 to improve current efficiency in the early stages (recommended but not essential as I understand it). Heat to 80 to 90 Deg C. Insert stainless steel elctrodes and pass 10A through the solution for ~18hrs while maintaining the temp.
Conversion is of the order of 98 - 99 %.

Little is said about subsequent extraction of the KMnO4 (the solution was apparently merely analysed to determine conversion ratios).
Perhaps it can be as simple as hot filtration followed by crystallization of the KMnO4. A quick bit of mental arithmetic implies a concentration of ~150g of KMnO4 in the approx 1Litre of solution.

To be determined:
1......Filtration and cooling will certainly recrystallize the KMnO4 , but is it soluble enough at 80 - 90 deg C to allow uncomplicated filtration of the xs MnO2?
2......Does the solution need to be neutralized or acidified to work up?
3......Will the electrodes give problems with the MnO2 deposits mentioned elsewhere? Ref Patent No 7 056 424
4.......Current density required?
5.......Will agitaiton be necessary?

There is the possibility that the mother liquor (after KMnO4 recrystallization ) can be reused as is for the next cycle. Simply add approx 1 mole each of MnO2 and KOH and repeat. It even has some KMnO4 left in it to help start the process.

If you guys have read the patent, this post is probably unnecessary, but I'm trying the get the small scale / improvised procedure straight in my own mind. Have I missed anything?

Ref Item #4

Current density is quoted as 5 - 50 mA/cm2 (converted)
Current Concentration is 3 - 30 A/Litre

At 10A the area of the anode is: 250 - 2500 cm2.
I assume the iron rod (or whatever ) cathode area is not an issue, but the problem would be easily rectified by using another cylindrical electrode.

I'm hoping that the resistive heating of the cell will supply a significant amount of the heat required to maintain the required 90 Deg C. Insulation and an idling hotplate under the reactor should do the job.

[Edited on 21-6-2007 by ciscosdad]
View user's profile View All Posts By User
DerAlte
International Hazard
*****




Posts: 779
Registered: 14-5-2007
Location: Erehwon
Member Is Offline

Mood: Disgusted

[*] posted on 20-6-2007 at 15:52


A few thoughts on the production of KMnO4

The paramount thing is to minimize the production of chlorate during the process. So I have been rac