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Topic: Electrolysis of NaHCO3  (Read 2458 times)

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Offline hanzdolo

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Electrolysis of NaHCO3
« on: January 18, 2019, 01:45:33 PM »
I'm new to chemistry and first I'd like to say, NO, I'm not trying to plate out sodium metal, in an aqueous solution, that's just ridiculous, lol(though I did see something on KOH but the product was less than desirable).

I am however trying to knock  CO2(g) Off and synth NaOH. Is that even possible?

The way I see the reaction carrying out is:

NaHCO3  +  H2:rarrow:

@Anode: CO2(g) + O2(g) + 2H+ ,

@Cathode: NaOH + H2(g) + OH-

Is that correct?

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Re: Electrolysis of NaHCO3
« Reply #1 on: January 18, 2019, 02:57:30 PM »
Is that even possible?

You will be electrolyzing water, only products will be H2 and O2. All other ions are just spectators (helping in charge transfer though).

I would expect HCO3- to slowly convert to CO32-. Not because of the electrolysis though, just because it is much more stable.
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Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #2 on: January 18, 2019, 04:24:53 PM »
Is that even possible?

You will be electrolyzing water, only products will be H2 and O2. All other ions are just spectators (helping in charge transfer though).

I would expect HCO3- to slowly convert to CO32-. Not because of the electrolysis though, just because it is much more stable.

Wow, totally not what I expected. I figured being  when I react the solution with MgSO4 I get an immediate precipitate (unlike NaHCO3, which I have to heat or wait very long for the reaction to reach equilibrium), I was in fact producing NaOH, but I guess I was wrong.
It did give me a mild chemical burn when it got on my hands, but it was more like a H2O2 burn (I know H2O2 is unlikely).

Would a high voltage (12V with 83A available)  have any strange effects? 

I'm not arguing the point as you are far more knowledgeable in this area (my field is Engineering, Electrodynamics, I'm loving Chem though), I'm just trying to get answers to some strange occurrences.
Yesterday it very briefly smelled of ammonia, but when I came back an hour later to take a sample and try reacting with copper hydroxide to see if it would form the tetraamine complex, the ammonia smell was gone.  It also smelled of O3 when started the electrolysis @12V.
once I'd noticed, I brought it down to 6V, but it did run at 12V for a few hours before I'd noticed.

 

 


Offline chenbeier

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Re: Electrolysis of NaHCO3
« Reply #3 on: January 19, 2019, 12:05:47 PM »
I think the problem is your power supply, normaly you would have currents about 1-2 A . But 83 A will work like a welding iron . You get sparks and smell of Ozone.

What is the concentration of your solution and its conductivity. What kind of electrodes are you using?

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #4 on: January 20, 2019, 03:07:56 PM »
I think the problem is your power supply, normaly you would have currents about 1-2 A . But 83 A will work like a welding iron . You get sparks and smell of Ozone.

What is the concentration of your solution and its conductivity. What kind of electrodes are you using?

PbO2 anode and a copper cathode. 454g NaHCO3/3.5L H2O.

I'snt higher current density better?

I have shunt resistors tied to the ground of all my cells. I'm looking at 14.8A  right now on ione of them.

I'm currently using an atx PSU from an old gaming machine. I wan't to spin a PSU for electrolysis, but I still haven't learned which parameters have to be controlled.




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« Last Edit: January 20, 2019, 03:19:13 PM by hanzdolo »

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #5 on: January 21, 2019, 03:51:23 AM »
What is the concentration of your solution and its conductivity. What kind of electrodes are you using?

(sorry forgot)
the meter read 1.95 but I think it needs new probes. 454g NaHCO3 to 3.5L H2O

Offline Shannon Dove

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Re: Electrolysis of NaHCO3
« Reply #6 on: January 22, 2019, 10:10:53 AM »
It should be very possible and practical to make sodium hydroxide at home with electrolysis. I won't give a step by step, but a dived cell , using porous clay divider, and stainless steel electrodes should work, the hydroxide should accumulate in the cathode department. Better yet, just use sodium chloride, although you will need something other than stainless steel for the anode because it will make free chlorine, hypochlorite, etc, etc

Offline Enthalpy

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Re: Electrolysis of NaHCO3
« Reply #7 on: January 23, 2019, 06:56:33 AM »
The ATX power supply may be able to provide 83A at +12V but it does so only if the load absorbs so much, which I don't quite believe with a home-built electrolytic cell. It would mean extremely wide and close electrodes, in addition to the concentrated electrolyte.

The power would be 1kW (a lot for an ATX power supply, more or less conceivable if the target computer has two big graphic cards), and since the electrochemical reaction drops little of the 12V, the power would heat the electrolyte, bringing 1L to 100°C in 7min. If you didn't see that, then the current was less - my bet.

ATX power supplies have also +5V and +3.3V outputs, which would be far better for electrolyses, to prevent unwanted reactions. The 3.3V output can often provide more current than the +12V, so a smaller ATX would fit an electrolysis cell with optimized dimensions. Or if the production pace matters, build several electrolysis cells and connect them in series.

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #8 on: January 27, 2019, 08:53:07 PM »
It should be very possible and practical to make sodium hydroxide at home with electrolysis. I won't give a step by step, but a dived cell , using porous clay divider, and stainless steel electrodes should work, the hydroxide should accumulate in the cathode department. Better yet, just use sodium chloride, although you will need something other than stainless steel for the anode because it will make free chlorine, hypochlorite, etc, etc

I actually make Magnesium hydroxide and sulfuric acid from epsom salts that way, but I use PbO2 anode and I figured the constituents of clay were far too reactive so I used a pulverized glass and resin combo. Actually I've made Hydrochloric Acid and NaOH the way you described, I just find it easier (faster) to make the HCl+H2O by going the H2SO4+NaCl route though dangerous without the proper setup. Electrochemical route of NaOH || HCl+H2O production kicks off alot of HCl gas at different parts of the synthesis unless you make the NaCl solution basic which tends to end in perchlorates from what I understand.

The reason I tried to use NaHCO3 is because at the time all I had was the big lead anodes that I'd cast and I knew they'd make the PbO2  in solution where I didn't have to waste any H2SO4 while producing my lead dioxide anode (which takes much longer but seems to stand crumble less) and some much needed NaOH.

Using using the glass membrane I've had a great deal of success but a bit of issue producing the acid without a salt contamination.  Is there a point when the anions all move into the oxidation chamber and the cations all move into the reduction chamber?


Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #9 on: January 30, 2019, 03:22:42 PM »
The ATX power supply may be able to provide 83A at +12V but it does so only if the load absorbs so much, which I don't quite believe with a home-built electrolytic cell. It would mean extremely wide and close electrodes, in addition to the concentrated electrolyte.

The power would be 1kW (a lot for an ATX power supply, more or less conceivable if the target computer has two big graphic cards), and since the electrochemical reaction drops little of the 12V, the power would heat the electrolyte, bringing 1L to 100°C in 7min. If you didn't see that, then the current was less - my bet.

ATX power supplies have also +5V and +3.3V outputs, which would be far better for electrolyses, to prevent unwanted reactions. The 3.3V output can often provide more current than the +12V, so a smaller ATX would fit an electrolysis cell with optimized dimensions. Or if the production pace matters, build several electrolysis cells and connect them in series.

Okay, judging by your answer, you seem to know your electrodynamics. The surface area of the anode is 0.15m2 and you are correct as an ATX supply is a constant voltage supply only increasing current as the load demands.  The last one I ran was at like 6.9A 12V. You are correct again about the machine it came from(older SLI).

I really hope you don't mind answering a few questions as you're probably the only person on any of these message boards that actually picked up on everything. It seems we can speak a similar language.

I blew the supply the other day and I've got a bunch of High voltage MOSFETS, EE42/15's, etc.. lying around so I figured I'd spin a converter, but obviously voltage mode supplies aren't the best choice so I'm guessing CC, but there's still some stuff I need to figure out.

It's kinda difficult to explain without writing a book on this thin

I've been making different acid by pulling the anions through the membrane of an oxidation chamber(just, what I'm calling it, I'm sure there's a better name) by putting a saturated salt solution in the reduction chamber and little to no electrolyte in the oxidation chamber.  I'm sure you can imagine that this poses a bit of an issue, because in order to get it going I have to start at an insane voltage (170VDC mains rectified), once I see there's sufficient current throughput on the shunt resister, I have to switch to 12V manually.

That would lead one to believe that as long as you maintain a constant current voltage doesn't matter, but then there's the synthesis taking place which wants to be at a specific potential in order to produce the desired species.

Do I really have to wind a transformer and PFC inductors(was thinking about going with an interleaved PFC circuit) with full galvanic isolation or can I save it for something more important and make a buck converter with a couple of trimpots on comparators to control the VMAX and IOUT?

The confusing part is when I look at standard reduction potentials table, the range is from -4.101 -> 3.27V  which is really just 0-7.371V. (What happens  when you exceed that voltage aside from heat?). I understand that in order to induce certain reactions there has to be a certain potential applied to the solution, but In the case of acid production, I've had the best results with virtually no electrolyte in the oxidation chamber and the salt solution in the other. To get ~500mA flowing I have to start it up at full rectified 170VDC, once sufficient electrolyte has arrived at the anode I have to quickly turn the voltage down or it will destroy the reaction vessel.

There doesn't seem to be any concise sources of information on electrochemistry. It seems EVERYONE teaches the CuSO4 | ZnSO4 battery and NaCl electrolytic cell(which is a horrible example for a novice because it produces chlorine gas if  the solution isn't basic). Do you know a good source of info on the topic?




Offline Enthalpy

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Re: Electrolysis of NaHCO3
« Reply #10 on: January 31, 2019, 06:52:07 PM »
I don't know a simple book on electrochemistry. The topic itself is tricky, and I'm by no means an expert.

170V is indeed an awful lot in a bath, badly dangerous. I got once 110V (in Brazil) across the body in a shower and I testify one better avoids it. Very short time, not 240V, still alive. Do you have other means, like adding some electrolyte right from the beginning?

Do keep an insulation transformer. The mains and electrolytes don't go together.

The insulation doesn't need to come from a Power Factor Correction stage, and often the PFC doesn't insulate. PFC is "only" a legal requirement in Europe at the power you operate, not a technical one. You can just rectify and filter the mains, build a buck regulator, and obtain the output power from a secondary winding rather than using a simple coil. The inductive component (then a transformer) is marginally bigger, but for kW power, everybody would have a transformer, because an H full bridge can drive it, and then all components are smaller: transistors, diodes, inductive components.

I just wonder how used you are to power electronics, a difficult area. If you want to learn, that's perfect, and some good books exist. But if you hope to make a 1kW 12V supply as your first project, it will take you many months (with solid background in analog electronics and in electromagnetics, among others to estimate stray inductances and their effect at 83A 12V) and some money in destroyed components. So if it's merely a means to continue your electrochemistry experiments, stick to PC power supplies. As an other advantage, they are insulated.

==========

What else happens if the voltage is too high? In short: nobody knows, but things do happen, and never what is desired.

12V is already too much and usually lets the electrodes react, in addition to heating the electrolyte. The useful processes take place at 1V to 3V. If the computed voltage is higher, the process is probably impossible in water. Hence my suggestion to use the 3.3V or maybe 5V outputs of the PC power supply.

The general way to increase the intensity is bigger electrodes closer to an other, and more concentrated electrolytes. The next step is many cells, then connected in series for convenient current and voltage.

==========

About NaHCO3 (but I guess your experiments are more varied), what about heating it? I expect
NaHCO3 :rarrow: Na2CO3 :rarrow: Na2O
much like CaO is produced from CaCO3. Wiki suggests 851°C
https://en.wikipedia.org/wiki/Sodium_carbonate
which is accessible.

Offline Shannon Dove

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Re: Electrolysis of NaHCO3
« Reply #11 on: February 08, 2019, 01:39:51 PM »
I don't know how to quote text, but hanzdolo, I am very interested in your work. Tell me your opinion about this idea,... In a divided compartment cell, I used salt water in both compartments, then added some bone Ash to the anode compartment, as it got acid enough, the bone edge finally dissolved, I was hoping topull the calcium and sodium ions out of the anode compartment to make hydrochloric and phosphoric acid. What is your thoughts on this idea?

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #12 on: February 08, 2019, 04:35:10 PM »
I don't know a simple book on electrochemistry. The topic itself is tricky, and I'm by no means an expert.

170V is indeed an awful lot in a bath, badly dangerous. I got once 110V (in Brazil) across the body in a shower and I testify one better avoids it. Very short time, not 240V, still alive. Do you have other means, like adding some electrolyte right from the beginning?

Do keep an insulation transformer. The mains and electrolytes don't go together.

The insulation doesn't need to come from a Power Factor Correction stage, and often the PFC doesn't insulate. PFC is "only" a legal requirement in Europe at the power you operate, not a technical one. You can just rectify and filter the mains, build a buck regulator, and obtain the output power from a secondary winding rather than using a simple coil. The inductive component (then a transformer) is marginally bigger, but for kW power, everybody would have a transformer, because an H full bridge can drive it, and then all components are smaller: transistors, diodes, inductive components.

I just wonder how used you are to power electronics, a difficult area. If you want to learn, that's perfect, and some good books exist. But if you hope to make a 1kW 12V supply as your first project, it will take you many months (with solid background in analog electronics and in electromagnetics, among others to estimate stray inductances and their effect at 83A 12V) and some money in destroyed components. So if it's merely a means to continue your electrochemistry experiments, stick to PC power supplies. As an other advantage, they are insulated.

==========

What else happens if the voltage is too high? In short: nobody knows, but things do happen, and never what is desired.

12V is already too much and usually lets the electrodes react, in addition to heating the electrolyte. The useful processes take place at 1V to 3V. If the computed voltage is higher, the process is probably impossible in water. Hence my suggestion to use the 3.3V or maybe 5V outputs of the PC power supply.

The general way to increase the intensity is bigger electrodes closer to an other, and more concentrated electrolytes. The next step is many cells, then connected in series for convenient current and voltage.

==========

About NaHCO3 (but I guess your experiments are more varied), what about heating it? I expect
NaHCO3 :rarrow: Na2CO3 :rarrow: Na2O
much like CaO is produced from CaCO3. Wiki suggests 851°C
https://en.wikipedia.org/wiki/Sodium_carbonate
which is accessible.
LOL, sorry for the lack of clarity, I was referring to the necessity for galvanic isolation as opposed to going with a simple buck converter circuit. The reason for an interleaved PFC is that the PFC circuit actually serves to reduce stress on the MOSFETs and allow for thinner primary  as they'll be dealing with 400V @ 2.5A vs 170V @5.88A and if it's interleaved, it permits for smaller filter capacitors on the output due to a tremendously reduced ripple. 

I just figured with a buck circuit I could actually use a current mode design where it would output the necessary voltage to supply the desired current across the cell, howeve, I've found that too high of a voltage generated too much heat so I've decided to go the full bridge route.

I did in fact produce NaOH. I left the beaker of solution aside and a very unlucky housefly fell in it, so I left it there to see what would happen and it turned the fly to a dark spot at the bottom. then I tested it with aluminum foil and it reacted appropriately.

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #13 on: February 09, 2019, 04:13:22 AM »
I don't know how to quote text, but hanzdolo, I am very interested in your work. Tell me your opinion about this idea,... In a divided compartment cell, I used salt water in both compartments, then added some bone Ash to the anode compartment, as it got acid enough, the bone edge finally dissolved, I was hoping topull the calcium and sodium ions out of the anode compartment to make hydrochloric and phosphoric acid. What is your thoughts on this idea?

Okay, if you're trying to attract the cations (Ca+ Na+) to the cathode and leave behind a pure solution, I've found it works best if you can dissolve the salt in the cathode(reduction) chamber and allow the anode to pull your anion into the anode (oxidation) chamber you end up with the least contaminants in the end product. Which I guess doesn't really matter if you plan to distill your acid, but a good example of why you would want to avoid contaminants is during the distillation of the Product of a Sulfuric Acid electrochemical synthesis from MgSO4, it pops and spits violently as it precipitates MgSO4. Nasty business, that destroys glassware. 

For the sake of purity, I'd avoid making the acids together as you could make an amount of hydrochloric acid and/or sulfuric acid electrochemically and use it to knock the phosphate off of the bone ash. leaving behind calcium salt. I would recommend sulfuric as the sulfate salt is not water soluble and you can filter out of solution leaving behind Phosphoric acid and water which you can then further purify.

There are a number of reasons why you should just make sulfuric electrochemically.

1. The Easiest synthesis of H2SO4 is via electrolysis.
2. SO3 will not go all gaseous and deadly like Cl as it likes to be stable
3. You can make any other acid from their salt with H2SO4

I believe H2S208 (peroxydisulfuric) can also be prepared in this manner.  I've experimented with synthesis of MgS2O8 from MgSO4 and it did oxidize copper which is a property exhibited by peroxydisulfates as they are used as etchants. i haven't done any further experimentation in this area so  the results are still inconclusive.

An interesting process to conduct electrochemically is  to synthesize chlorine bleach (NaClO) from table salt via oxidation in a basic solution. This is quite the practical synthesis because pure bleach is rather difficult to procure otherwise and you can use the bleach in many other reactions, like producing ferrate (an extremely powerful oxidizer that can oxidize chromium to dichromate) or chloroform which us an extremely useful solvent.

I believe if you keep the bleach reaction going you can produce perchlorate, but I haven't performed the synthesis yet.

Offline hanzdolo

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Re: Electrolysis of NaHCO3
« Reply #14 on: February 09, 2019, 03:58:45 PM »
It should be very possible and practical to make sodium hydroxide at home with electrolysis. I won't give a step by step, but a dived cell , using porous clay divider, and stainless steel electrodes should work, the hydroxide should accumulate in the cathode department. Better yet, just use sodium chloride, although you will need something other than stainless steel for the anode because it will make free chlorine, hypochlorite, etc, etc

Today I'm going to try it as if I were making an acid, where I'd be pulling HCO3 into the oxidation half cell from the reduction half cell. I don't expect there will be any stable carbonic acid, but being the carbonic acid leaves solution, what gets left over?

I know at some point OH- will traverse the barrier from cathode to anode, but what happens to it?
Does hydroxide remain hydroxide when pulled  into hydronium?
Does it just become water or is there a way to produce peroxide?

There are a couple of other things I wanted to try, like electrodeless ionization of an aqueous solution using a high voltage arc, high voltage O3 production for direct synthesis of NaClO and H2O + O3  :rarrow: H2O2.

Do you have any experience in this area?

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