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Hector
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[*] posted on 3-11-2017 at 08:16
sodium permissive membrane


In the chlor-alkali process a membrane is used to make the production of sodium hydroxide possible. For an amateur who is trying to get the said NaOH from brine electrolysis, where do i get this "membrane" (what is it made of and where to find one)
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18thTimeLucky
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[*] posted on 3-11-2017 at 08:44


Funnily enough 'CaCl2' asked a very similar question a few days ago over in Reagents and Apparatus Acquisition.
http://www.sciencemadness.org/talk/viewthread.php?tid=77879

I made a reply there mentioning a blog post I have recently done on my own experience of the chlor-alkali process using cotton from cotton balls as the membrane. If you check out my blog post (there is a link in my signature) the post is called 'Synthesis of alkali metal hydroxides via electrolysis'.
Expensive commercial membranes are obviously going to be better in everyway but I had a good amount of success using cotton, and I doubt the availability of these commercial membranes compares to cotton for the amateur, so I do have to recommend it. The post is a bit long but it hopefully will cover every problem you will have and give you some insight into the process (it is less of a how-to and more of a story of my experiences).

I have heard of various other salt bridges and membranes, but I have no experience with them, just with cotton, so maybe somebody more knowledged will stop by and help out. Saying that, I am interested if anybody on SM has done a synthesis paper on this process. I will put it on my to do list to have a quick look on the archive.

I hope this helps.

[Edited on 4-11-2017 by 18thTimeLucky?]




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macckone
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[*] posted on 3-11-2017 at 19:17


obligatory UTFSE warning.

https://www.sciencemadness.org/whisper/viewthread.php?tid=77...
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Hector
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[*] posted on 6-11-2017 at 11:42


nice vlog man:)

so if i use cotton it would be ok for the purpose then
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18thTimeLucky
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[*] posted on 6-11-2017 at 12:00


Thank you! I'm glad I could be of help.

Yes, cotton should work as it did multiple times for me. I know you are new to Sciencemadness, but like macckone said please use the search engine and dig around a bit before posting a question in the future as people have asked very similar or the same questions before.




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[*] posted on 7-11-2017 at 05:59


I'd expect polyester fabric (PET plastic) to work better than cotton, however I posted a paper recently in this forum about using cross-linked polyvinyl alcohol as an alkali-stable divided-cell membrane. Cross-linking can be done with gluteraldehyde solution (used to disinfect medical devices) or by using periodate to cleave its occasional diol sites into aldehydes. PVA is subsidized by the Chinese government because it can be made from coal instead of oil, so it's in practically everything. Clear dollar-store glue contains nothing else besides water, most of the time.



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mysteriusbhoice
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[*] posted on 5-1-2018 at 02:25


Quote: Originally posted by Melgar  
I'd expect polyester fabric (PET plastic) to work better than cotton, however I posted a paper recently in this forum about using cross-linked polyvinyl alcohol as an alkali-stable divided-cell membrane. Cross-linking can be done with gluteraldehyde solution (used to disinfect medical devices) or by using periodate to cleave its occasional diol sites into aldehydes. PVA is subsidized by the Chinese government because it can be made from coal instead of oil, so it's in practically everything. Clear dollar-store glue contains nothing else besides water, most of the time.


Can i use sodium borate which is stable in alkaline conditions as a cross linking agent or will it slowly dissolve in the soln..

another thing is im using this to create sulfuric acid from sodium sulfate where the cathode side electrolyte is a paste of calcium sulfate and the anode side is a soln of sodium sulfate.

i want dat sodium to pass through in order to attack the calcium sulfate and convert it into insoluble calcium hydroxide.

this process worked using cotton but the membrane bridge started to heat up because the sulfuric acid conc got high that it started to react with some product from the other side.
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mysteriusbhoice
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[*] posted on 5-1-2018 at 05:57


I tested pva glue and sodium borate mix and it seems to hold up in both acidic and alkaline mediums
bad news is that its incompatible with HCl because the mix dissolves in HCl but not H2SO4 so using sodium sulfate as the electrolyte can work for my purposes if at all it works as an exchange membrane.
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Melgar
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[*] posted on 19-1-2018 at 22:42


Quote: Originally posted by mysteriusbhoice  

this process worked using cotton but the membrane bridge started to heat up because the sulfuric acid conc got high that it started to react with some product from the other side.

No, it's heating up because of electrical resistance. you need to increase the area of the interface between the half cells.




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