RU_KLO - 25-11-2022 at 11:39
Im starting with electrolysis (as with Chemistry as well)
After checking several videos on YT, I think that membranes are one of the most problematic issues.
So, as other of my experiments is getting lithium (and others) from Li ion batteries, the membrane is a "side product" of this procedure.
(and after cheching how li ion battery works -> cation exchange membrane)
With this in mind, i made a test (alkaly cell)
1) the membrane is small because batteries are small (membrane is max 10 cm x 10 cm - only one side is 10 cm, the other is 1m long - as is rolled in
the battery)
2) is hard (or maybe impossible) to glue - teflon like type of material
Used 2 90° pvc elbow pipes (i thinks its 3''). clean the membrane ( because of graphite stains), streched, cover one hole, and join the other 90°
elbow pipe. U shape was formed. Pipes where not glued (also membrane was not glued its held only by pressure.
Test:
1) filled one side of the cell with water. in 24 hs no water was seen on the other side.
2) made an alkally cell, with Na2CO3 in one side. dH2O on the other. (used Na2CO3 instead of NaCl because I wanted to left inside my laboratory "aka
living room" - no fume hood, and dont wanted Chlorine generation.....)
3) NaOH was produced, low current was used (< 250mA) becacuse didnt want to worn the graphite electrodes (used Ni electrode as Anode - from a NiMn
Battery , and 4 joined together D battery graphite rods as Cathode) .Voltage starded at 24V few mA, and after 2 days where at 5V 250mA - current
limited) .Done a fast (read inaccurate) titration, 0.2 M Naoh where obtained in 350ml H2O - volume was not meassured but calculated - so take these
figures with a ton of salt.... )
So at first impresion it worked.
Here are the questions:
1) is there another simple test for membrane permeability - instead of putting water at one side and not seein in the other?
(maybe adding some tincture in one side and checking in the other side???)
2) is there an method to check if not other cations/anions where permeated through the menbrane? (simple test if possible)
(for example H2SO4 in the anode chamber, H2O in the cathode chamber graphite as electrode, and checking for Sulfur in the cathode chamber - Will this
produce SO2? SO3?)
3) how to test/push the membrane, and detect failures? (I know that applying more current wil generate heat and push the mebrane, but how I detect if
it failed? (how to detect if Na2CO3 is present in the NaOH chamber? - for example. Maybe electrolisis for NaCl and testing for Chlorine ions on
cathode chamber?
4) although its a cation exchange chamber, which electrolysis could be tested, to test the membrane as Anion exchange membrane?
thanks,
Mateo_swe - 25-11-2022 at 13:08
Have you seen the YT videos and posts here on SM by forum member mysteriusbhoice?
Lots on electrolysis, DIY ion membranes, homemade cells, anodes/cathodes and similar, lots of intresting stuff.
Search for posts by mysteriusbhoice or look through posts in the "Technochemistry" section.
Heres a youtube video about DIY ion membranes by mysteriusbhoice
https://www.youtube.com/watch?v=tiMt4tIced8
Rainwater - 25-11-2022 at 19:12
I can vouch for his caton exchange membrane procedure. Tempature control during the heating processes is absolutely nessacery. Ive had better results
heating at a lower temperature for a longer period. My naoh cell get about 30% by weight before the consentration no longer increases. And the
membrane under 10 amps shows no signs of degrading. Yet.
Edit:
1) there is a test using h2 gas, basicly measuring the pressure drop when the membrane seals the end of a pressure vessel.
2) not 100% sure i understand your question. If you want to check if hco3- moved through the membrane, add some acid to a sample taken from
the cathode compartment. If it bubbles co2 then the bicarbonate has passed through the membrane.
3) see answer to # 2. Also keep records of cell performance, refreshments, and yields.
When you notice a change in these, then narrow down the cause. Change in power supply calibration, reagent contamination, consentration
4) that is a good question, looking forward to the answer
[Edited on 26-11-2022 by Rainwater]
macckone - 29-11-2022 at 20:36
All cations membranes transmit some anions.
Commercial membranes are 95%+ selective.
Some are as high as 99%.
They also are not generally selective for specific cations but larger cations move through slower and can even get 'stuck' effectively blocking the
membrane.
If it will transmit both anions and cations it is a diaphragm and not an ion selective membrane.