[kelaniz]

Greetings,

Apologies if this lands in the wrong forum. I've been ghosting here for a few weeks, and this is my first post, so cut me a bit of slack if possible.

A little background, I'm just another amateur chemist simply trying to learn. I'm studying chemistry partly for fun, partly because when my competency increases, I want to explore a few ideas I have involving thermoplastic polymers, and lastly, I'm planning a midlife career shift to enter medical school, and chemistry's by far my weakest skill. But enough about me...

At the risk of opening with a stupid question, I've got a multi-part question regarding good 'ol supersaturated NaCl brine electrolysis via a membrane cell. I can't seem to find a straight answer on a few safety and performance issues. Here goes.

Scenario: Electrolysis is interrupted halfway before completion. The brine tank is still pretty much saturated with NaCl and dissolved Cl. Here's the questions...

Question 1: What reaction would occur, and what is produced by dumping sodium bicarbonate / NaHCO₃ into that brine tank?

In case anyone wonders, I'm using my cell for experience, and to create a little extra hydrogen and dilute NaOH solution to save a measly $10. Due to my (apparently) ingenious design, the output is so efficient that I become the proud owner of too much pretty green water.

The excess Cl gas is safely vented outside, so that's not a problem. But the water...that's different. I want to neutralize the chlorine, preferably in a way that allows me to continue the electrolysis. In all my searches, I've seen quite a dozen posts that say dumping NaHCO₃ into the brine will neutralize the dissolved chlorine and release Na⁺ into the brine that will pass through the membrane, thus allowing electrolysis to continue -effectively removing the need to add more NaCl in the brine. However, I've also seen a few posts that say this isn't the case. So..

Question 2: If NaHCO₃ does neutralize dissolved chlorine, and make Na⁺ available, why can't I just use a supersaturated solution of NaHCO₃ instead of NaCl at the outset?

and...

Question 3: If that's not possible, out of curiosity, what would a membrane cell with this supersaturated solution of NaHCO₃ in water actually produce, anyway?

and finally...

Question 4: Assuming those dozen posters were wrong,  what would be the best/safest means of neutralizing the aqueous chlorine (other than NaHSO₃) and allowing electrolysis to continue, (that'd be a bonus. Neutralizing chlorine is the main goal.).

*whew*

Regarding question 2, when I tried to figure out the reaction & products for  NaHCO₃ combined with aqueous chlorine, my initial guess was that NaCl and a bicarbonate ion HCO3⁻ would be produced. However, upon actual mixing, lots of gas was released. I captured a sample. It didn't explode when subjected to flame, and it didn't smell like chlorine, so I figured it to be CO₂. Of course, that means my first guess must be completely wrong. So, now I'm at a loss

I apologize for posting such an involved question. Rest assured, while I have plenty of question I may ask in the future, I do try to stick to a policy of answering at least two questions for each one I ask (four for the incredibly stupid ones). Fortunately, there really are some areas of chemistry where I actually know what the hell I'm doing. This just isn't one of them.


Many thanks in advance to any roving chemguru who can answer these things for me. This looks like a great forum, and I look forward to getting to know a few people here and posting something useful in the future.

Thanks again,

-kel

[AWK]

Cl2 + H2O = HCl + HOCl
HCl + NaHCO3 = NaCl + CO2 + H2O
Chlorine partially dissolves in water, then reacts according the first reaction.

[kelaniz]

Thanks for the quick answer, AWK. You definitely cleared up Parts #1 and #4.

However, I'm still not clear on parts #2 and #3. If the brine was fresh, and there was no Cl or HCl in solution, what would electrolysis using a saturated NaHCO3 solution instead of NaCl create?

I'm fairly sure it would work, but I don't know what the resulting products would be. Even if it won't work, It's still good to know I can neutralize the chlorine cheaply. Also, the next version of my cell was being designed to automatically replace chlorinated water with clean brine, but if I can simply refresh the brine by adding NAHCO3, that'll be MUCH easier to implement. It sure beats adding two pumps and a holding tank.

-Kel

[AWK]

Electrolysis of NaCl
2H3O+ + 2e- = 2H2O + H2(g)
2Cl- = Cl2 + 2e-
Electrolysis of NaHCO3
2H3O+ + 2e- = 2H2O + H2(g)
2HCO3- = H2O + 2CO2 + 2e-

[kelaniz]

If I understand that reaction correctly (not very likely ), NAHCO3 electrolysis would work similarly to NaCl, but CO2 forms at the anode instead of Cl?

Thanks again.

[billnotgatez]

If it is not top secret can you post a picture of your system?   Let us know if it is totally homemade.  Could you also post a diagram of how it works and what you used for the membrane?

[kelaniz]

Sure, I can post a diagram. I'll find and scan my original blueprint, or just photoshop a basic overview this weekend when I'll have some free time. It's just a one-trick pony membrane cell, so it's not that complex, or much different from any other cell most of you have probably seen.

I could post a picture, but it wouldn't show much. The entire assembly is housed in a sealed ventilation box with only a tiny window.  It is homebuilt, but I like to think it's of a quality that's not quite lab-grade, but much nicer than a pile of hot-glued Tupperware and aquarium tubing

The original membrane was a 1" square Nafion film, reinforced by polyester fabric and sandwiched (like a window) between the fused walls of two HDPE tanks.  Unfortunately, during a cleaning, I inadvertently damaged the membrane, so until I can replace it, I installed a square block of 1/2" long pieces of 1/4" (i.d.) glass tubing. The block itself, and the spaces surrounding each tube is sealed, and the tubes themselves are packed with a few very thin layers of cellulose sponge and neoprene. It's a hack, I'll admit, but it works without leaking.

Anyway, I'll try to dig up that diagram and post it sometime this weekend.

-Kel