Sciencemadness Discussion Board

Nafion Cell for Chloro Alkali

chemistry4frog - 19-8-2023 at 20:19

Can I use nafion n117 sandwiched between two MMO anodes to generate hydrogen and chlorine gas and hydrogen gas ? I was thinking glass fish tank with acrylic divider cut with a square hole for the nafion membrane which is caulked to the acrylic plate, with MMO mesh anodes attached to each side.

The top of the fish tank will have a lid with pipes for hydrogen and chlorine gas collection.

The chlorine is used for chlorine reactions. Needed yield is around 24 Liters / hour. Would a 100mm x 100mm nafion sheet work. Does the nafion need pre-treatment.

Do you think the nafion will hold up? Will it wear away and need replacing all the time ? Can I just use road salt super saturated in water for the anode water.


[Edited on 20-8-2023 by chemistry4frog]

Rainwater - 20-8-2023 at 03:11

Quote: Originally posted by chemistry4frog  
Can I use nafion n117 sandwiched between two MMO anodes to generate hydrogen and chlorine gas and hydrogen gas?

Depending on your solutions yes
Quote:
Needed yield is around 24 Liters / hour. Would a 100mm x 100mm nafion sheet work.

Show your equations and the math involved, and calculate the current needed.
Then figure out the proposed current density
Quote:

Does the nafion need pre-treatment.

no but it helps
Quote:

Do you think the nafion will hold up? Will it wear away and need replacing all the time ?

Depends on all of the above answers and the exact conditions your cell will be maintained at. Ph, current density, temperature, osmotic pressure.

chemistry4frog - 20-8-2023 at 09:42

For the anode half-reaction:
E(anode) = 2 * 96485 C/mol * 4 V = 385940 C∙V/mol = 385940 J/mol =
0.1kwh

current density is 100wh / 4 volt = 25 amps per 100mm^2 = 2500 amps per meter squared.

is this correct and feasible for n117 nafion?

Rainwater - 20-8-2023 at 13:31

Without writing it out fully, its difficult to understand your numbers.

This is a textbook problem, with a lot of principles already discussed on this forum.
To directly answer your question, you need to know how much the membrane will be heated, and how much thermal dissipation your appratus has. Heat will destroy the membrane, with nafion, it will dehydrate the polymer causing cracking.

https://www.google.com/search?q=site%3Asciencemadness.org+sa...

[Edited on 20-8-2023 by Rainwater]

chemistry4frog - 20-8-2023 at 13:35

can the anode mesh directly touch the nafion will it puncture or damage it, if the nafion swells.

khlor - 20-8-2023 at 13:55

Quote: Originally posted by chemistry4frog  
... with MMO mesh anodes attached to each side.
[Edited on 20-8-2023 by chemistry4frog]


Look, I may or may not know what I am talking here. But please understand that I am talking from experience and pain here. So take it as a cautionary tale and if any experts see this and have any explanation and means to avoid what happened with me, I'll be grateful.

So, MMO anodes on a chlor-alkali cell, I tried once, a cell divided by a ceramic/clay/kaolin/whatever that is diaphragm. and I mail just arrived with my so awaited MMO electrodes. I assembled my cell and started the PSU, few minutes go by and no chlorine(what I wanted out of it) I ramp up the current, I see hydrogen but not a single wiff of chlorine. then I disassemble the cell and horror met my eyes, all the power was going to convert all the expensive materials of the MMO mesh into useless chlorides of their respectives metals, the color was beautiful, but I almost cried blood. during some more research(feels like all I am doing nowdays) and turns out that anodic conditions on chloralkali cells can indeed corrode even platinum, thus, to this day, I fail to understand what the industry does to prevent this,. I tested whatever was left of the MMO mesh to recover some copper metal out of solution and it worked fine, no corrosion on the MMO mesh used as anode, but to this day I fear of putting it on another divided cell and I am using graphite to this day. this happened over two years ago and still left me scarred for life to see so much money go into solution and yet accomplish nothing. sorry for the rant, I still didn't got over it.

[Edited on 20-8-2023 by khlor]

chemistry4frog - 20-8-2023 at 16:15

did you use iodized table salt or pure nacl ?? someone on the forum mentions that the mmo can passivate. also was the salt water super saturated? they say low chloride concentration passivates the anode.

[Edited on 21-8-2023 by chemistry4frog]

[Edited on 21-8-2023 by chemistry4frog]

[Edited on 21-8-2023 by chemistry4frog]

khlor - 20-8-2023 at 18:10

The anode wasn't passivated, it dissolved. Heck! even the titanium substrate wasn't safe. Yes, iodated table salt, though I never heard of it being an issue. And the solution was over saturated.

mysteriusbhoice - 21-8-2023 at 02:32

ive ran these before and iodized salt isnt usually the problem as there are mentions of Ir-Ru making periodate using potassium or sodium iodide but its the issue with the additives in the salt like ferrocyanide and calcium silicate thats the issue. But I would oversaturate the anode chamber and keep salt always present at the bottom to allow chlorine to not dissolve. I would also suggest using Ir-Ta instead as its more resistant to pH changes and will tolerate even zero chloride levels but at the cost of +0.3V higher operating voltage to achieve the same current density.

[Edited on 21-8-2023 by mysteriusbhoice]

chemistry4frog - 21-8-2023 at 06:26

Hey mysterious bhoice, for your hydrchloric acid cell, how long did your ionemer cement resin last.

The problem is that I would like to make around 8 Liters of HCL per day at 12 M = 96 moles per day.

The issue is that I think you need for 1 mol of Cl per hour you need:
1 electron x 96,000 columb / 3600 = 26.6 amps.

26.6 x 96 / 24 = 96 amps roughly.

The problem is what membrane area could I use to handle 96 amps? Nafion N117 or your membrane I am not sure what the amps per cm^2 are ?
Is it better for me to use your thick ionemer cement thing as that seems very robust but I think the efficiency might be poor ?

For your membrane videos what was the current per cm^2 you could draw in your paper towel membrane and also your casted cement membrane. Was your casted cement membrane a decent conductor or does it melt at 96 amps due to I^2 R.

I will have cooling in the system. Basically, there will be pumps to pump the electrolyte in and out of the cell to cool against a heat exchanger.

[Edited on 21-8-2023 by chemistry4frog]

[Edited on 21-8-2023 by chemistry4frog]

chemistry4frog - 21-8-2023 at 15:23

Quote: Originally posted by mysteriusbhoice  
ive ran these before and iodized salt isnt usually the problem as there are mentions of Ir-Ru making periodate using potassium or sodium iodide but its the issue with the additives in the salt like ferrocyanide and calcium silicate thats the issue. But I would oversaturate the anode chamber and keep salt always present at the bottom to allow chlorine to not dissolve. I would also suggest using Ir-Ta instead as its more resistant to pH changes and will tolerate even zero chloride levels but at the cost of +0.3V higher operating voltage to achieve the same current density.

[Edited on 21-8-2023 by mysteriusbhoice]


can lead dioxide be used as an anode in the chloro alkali cell for hcl generation.

mysteriusbhoice - 22-8-2023 at 01:48

Quote: Originally posted by chemistry4frog  

can lead dioxide be used as an anode in the chloro alkali cell for hcl generation.

nope you should avoid that for such a cell as it doesnt like chlorine evolution and will be destroyed in a chloro alkali cell.

chemistry4frog - 22-8-2023 at 05:31

Quote: Originally posted by mysteriusbhoice  
Quote: Originally posted by chemistry4frog  

can lead dioxide be used as an anode in the chloro alkali cell for hcl generation.

nope you should avoid that for such a cell as it doesnt like chlorine evolution and will be destroyed in a chloro alkali cell.



Hey mysterious bhoice, for your hydrchloric acid cell, how long did your ionemer cement resin last.

The problem is that I would like to make around 8 Liters of HCL per day at 12 M = 96 moles per day.

The issue is that I think you need for 1 mol of Cl per hour you need:
1 electron x 96,000 columb / 3600 = 26.6 amps.

26.6 x 96 / 24 = 96 amps roughly.

The problem is what membrane area could I use to handle 96 amps? Nafion N117 or your membrane I am not sure what the amps per cm^2 are ?
Is it better for me to use your thick ionemer cement thing as that seems very robust but I think the efficiency might be poor ?

For your membrane videos what was the current per cm^2 you could draw in your paper towel membrane and also your casted cement membrane. Was your casted cement membrane a decent conductor or does it melt at 96 amps due to I^2 R.

I will have cooling in the system. Basically, there will be pumps to pump the electrolyte in and out of the cell to cool against a heat exchanger.

mysteriusbhoice - 22-8-2023 at 20:23

The cement membranes are less conductive if they are too thick but are very robust. I recommend adding fiberglass as reinforcement to make thinner membranes made of ionomer cement. Nafion membranes can only handle up to 200ma/cm^2 and for 96 amps you need several stacked cells but ionomer cement doesnt care how much current you run it because its literally a rock with conductive polymer or salts like CaSO4 to exchange ions.

I recommend nafion if you have a limited number of electrodes and plan to run at high current density but if you want to have multiple stacked cell chambers at lower current density around 80ma/cm^2 then you can use ionomer cement because its less conductive than nafion.

I still think for 96 amps you will need 5 or 6 anode chambers and 5 Ir-Ta anodes are pricey and Ir-Ru will shit itself if shit goes wrong.

[Edited on 23-8-2023 by mysteriusbhoice]

chemistry4frog - 23-8-2023 at 07:08

Quote: Originally posted by mysteriusbhoice  
The cement membranes are less conductive if they are too thick but are very robust. I recommend adding fiberglass as reinforcement to make thinner membranes made of ionomer cement. Nafion membranes can only handle up to 200ma/cm^2 and for 96 amps you need several stacked cells but ionomer cement doesnt care how much current you run it because its literally a rock with conductive polymer or salts like CaSO4 to exchange ions.

I recommend nafion if you have a limited number of electrodes and plan to run at high current density but if you want to have multiple stacked cell chambers at lower current density around 80ma/cm^2 then you can use ionomer cement because its less conductive than nafion.

I still think for 96 amps you will need 5 or 6 anode chambers and 5 Ir-Ta anodes are pricey and Ir-Ru will shit itself if shit goes wrong.

[Edited on 23-8-2023 by mysteriusbhoice]


Yeah thats the plan. I will buy cation ion exchange resin and cast a bunch of ionemer cement. 5 or 6 chloro alkali units would be sufficient. Probably will need to be pushing 150 amps total due to inefficiency losses in the absorption and collections of gases which is fine.

_____________________________

Are IR-RU anodes that bad for this setup ? I am having a hard time finding Ir-Ta anodes on aliexpress. Is a copper cathode ok ?

[Edited on 23-8-2023 by chemistry4frog]