styren - 15-11-2012 at 03:13
Hello everybody!
I have some questions about the electrolysis of brine. I want to produce chlorine and hydrogen. I've build a simple setup. Two plastic tubes, both of
them sealed at one end, with electrodes in them and tubing coming out from the side of each. I've used silicone to make it air tight.
After inserting those tubes into brine i let current run through it. After a couple of minutes I can smell chlorine coming out of the tubing but
there's no sign of hydrogen in the other. I can't figure it out why. I think that it may just escape but everything looks nicely sealed and air tight.
Can anyone give me any good advice?
Also:
What voltage is the best for producing chlorine and hydrogen from brine?
How much amps per square cm of an electrode?
How long will it take to liberate one mole of Cl from one mole of NaCl?
At what concentration of brine chlorine is not produced anymore, or the rate of it's liberation is significantly lowered?
CHRIS25 - 15-11-2012 at 03:30
http://scienceaid.co.uk/chemistry/applied/electrolysis.html
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Elect...
I have not looked properly, but these are two references I had. But have not read them for some time to see if they answer any questions.
Page two and three of this document seem to tackle a couple of questions on your list. (I know little about the maths of all this so forgive me if I
waste your time)http://edudigm.in/downloads/DP_Electrochemistry.pdf
[Edited on 15-11-2012 by CHRIS25]
[Edited on 15-11-2012 by CHRIS25]
elementcollector1 - 15-11-2012 at 10:11
Funnily enough, I often notice hydrogen appearing and bubbling far more rapidly than chlorine. I'll try to answer your questions as well.
-Voltage: Preferably fairly high, although for isolating gases, there's no real limit to voltage short of boiling the water (although if you really
made a setup like that...)
-Amps per cm^2: No idea, as I don't know enough about this topic to calculate it.
-How long to liberate one mole of Cl2: Depends on current density, efficiency, etc. The more the better, as they say (but don't use house current or
anything like that. Use a car battery charger instead.)
-At what concentration of brine is chlorine production lowered significantly? -VERY DILUTE. Dilute enough to not be worth running the cell in the
first place, in my opinion.
@CHRIS25: The sites were good as usual, but I would like to point out one very important flaw: -The electrolysis of brine in these setups does NOT
produce NaOH. Any NaOH thus produced immediately reacts with dissolved chlorine in the brine to first make sodium hypochlorite (bleach). Then, if
concentration of brine is high enough and the electrodes are close together with a good deal of current, sodium chlorate is produced. Under special
conditions, sodium perchlorate can be produced. The only way to produce NaOH by the electrolysis of brine is to split the cells, either by a diaphragm
down the center or by a salt bridge.
Rant over, thanks for reading. 
m1tanker78 - 15-11-2012 at 16:54
Are you trapping the gases somehow?
If my math is correct, @1A you should produce roughly 1.3g of chlorine per hour. At this rate, it would take ~ 27 hours to produce (but not
necessarily liberate(!)) one mole of chlorine. I imagine much of it dissolves and reacts so it's hard to say how much would be liberated in reality.
Tank
tetrahedron - 15-11-2012 at 17:23
actually for one mole of chlorine atoms that get oxidized only half a mole of diatomic chlorine gas is produced (assuming 100% liberated).