Sciencemadness Discussion Board

I'm looking into making zinc bromide in sizable quantities

zimirken - 15-3-2018 at 07:51

Hello everyone,

I'm a mechanical engineer with many hobbies. This summer I want to experiment with homemade batteries. So I've looked into the various types of batteries to figure out what kind are feasible to make at home. Now, I'm not talking about no lemon batteries, I want real useful storage. The impossible pipe dream eventually bieng building my own battery bank for offgrid solar living. Obviously that's not likely to happen, but it would be nice to build a little electric scooter or something.

I originally was going to make lead acid batteries, as it would be pretty easy to machine a mold and cast lead plates. However more in depth research showed that the only type of lead acid battery construction that ever had any real storage capacity was the pasted plate design. Looking into making lead paste showed that it was difficult to do on a non industrial scale. You need lots of alloying elements and huge ball mills and humidity controlled furnaces and stuff like that. I saw a youtube video where someone made their own zinc bromine battery, and while it was light on resulting numbers, and they said it accepted a good charge rate for a small battery. It also doesn't require any exotic materials or methods. Basically just carbon felt electrodes in a solution of zinc bromide.

So I started looking into getting zinc bromide, and boy is it expensive. China wanted ~$150 per kilo for anything less than a 55 gallon barrel of the stuff. Various chemical suppliers online wanted ~$60 for 100 grams. I would most certainly want at least a couple pounds of the stuff to be able to make batteries big enough to do real electrical testing on. While I could spend a few hundred dollars on enough zinc bromide, I would much rather spend the money on chemistry equipment. From my research it seems fairly simple to convert sodium bromide into zinc bromide. Since I can get sodium bromide pool chemical for <$10 a pound, It will be far more cost effective.

So I've decided that my summer project is going to be making zinc bromide from sodium bromide. It's looking to be a big somewhat dangerous project, but that's something I'm no stranger to. I've been working with lethal high voltage energy storage capacitor banks since I was in high school. My FiL is also a college chemistry professor, who I am involving in this project. I'm very used to researching all necessary safety precautions, and cost is not a good reason to take shortcuts when it comes to safety. I am aware that I can only use teflon and viton type materials for things like hoses.

TLDR: I want to make zinc bromide(aq) from sodium bromide for making batteries.

From my research there seems to be three GOOD ways to do what I want, and two of them involve making elemental bromine. Remember, I don't want a couple grams of this stuff, I want to be able to make a lot of it with high yield rates. Also, I'm limited to off the shelf reagents for cost effectiveness.

The first method is to make hydrobromic acid and mix it with zinc oxide.
You mix sulfuric acid with sodium bromide to make hydrobromic acid. Then you distill the HBr over to another container with water and zinc oxide powder. Zinc oxide powder is more expensive than zinc metal, and maybe my priorities are backwards but distilling acid sounds more dangerous than distilling bromine. It also looks like this reaction is super exothermic, which makes things more risky. Also, sulfuric acid drain cleaner is more expensive than muriatic acid.

The second method is to use Chlorine tablets and muriatic acid to displace the bromine, and then distill the bromine over into a container with zinc and water.
This method seems like a good way to do things. You just make a solution of sodium bromide and chlorine tablets, then slowly drip HCl into it to make bromine. Then you distill the bromine over into a flask with water and zinc and the bromine eats the zinc and makes zinc bromide in solution. I'm not really sure what the difference is between this method and the next method besides not having chlorine gas, but there must be a disadvantage to this method because there are more youtube videos of the next method than there are of this method.

The final method is to drip HCl on chlorine tablets to make chlorine gas, then bubble it into the sodium bromide solution to displace the bromine. Then you distill the bromine into the water zinc container.
This method has two obvious disadvantages compared to the previous method. Notably requiring three reactors instead of two, and having to work with chlorine gas. You can also generate chlorine gas by electrolyzing salt water instead of using the reaction. This way to generate the chlorine is probably more controllable and less risky. Plus the only reagents you need are zinc, sodium bromide, and salt.

Regardless of the method, I plan on doing this all in as safe of a manner as I can reasonably do. I'll be constructing a fume hood in the barn. I also plan on sealing the system and having tubes from each reactor going into a beaker filled with base water. That way I can capture any chlorine or bromine and keep it from even entering the atmosphere.

Now, I'm not super knowledgeable on chemistry, although I plan on learning as much as I can in the coming months. Plus I'll have help from my FiL.

TLDR: Help me decide which method to use to make a lot of zinc bromide with low reagent cost and high yield. Also maybe double check me to make sure I'm not forgetting any big safety issues.

[Edited on 3-15-2018 by zimirken]

Meltonium - 15-3-2018 at 08:09

In my experience with liquid bromine, I would certainly not suggest doing that to make zinc bromide. Although it is easy to make liquid bromine in this way, doing the reaction with zinc is likely to be exothermic and due to bromine's high vapor pressure, not much of the bromine would react with the zinc.
I would urge to go the hydrobromic acid route. When you distill off the azeotropic HBr, there may be excess HBr gas coming with it. By running this over the zinc metal, you may be able to increase yield. Also, since there is water with the hydrobromic acid, it will serve to absorb a lot of the heat generated.
I am no expert though.
You may want to try a very small scale run of both methods and see which give the better yield and which is easier/more cost effective for you to do.

Sulaiman - 15-3-2018 at 08:17

My first thoughts;
. have you made a working, reliable small-scale battery before scaling up ?
. bromine or chlorine in large quantities is not like small scale where accidents can be survived
. I believe that if you add up the time.effort.cost of research.development.replacement.disposal
then you will consider commercially made cells..

Plunkett - 15-3-2018 at 08:25

What about mixing zinc chloride (solubility 0.98 kg/L) with sodium bromide (solubility 0.80 kg/L) and using recrystallization to separate zinc bromide (solubility 3.8 kg/L) and sodium chloride (solubility 0.35 kg/L)? All solubilities are quoted at 0 °C.

[Edited on 16-3-2018 by Plunkett]

zimirken - 15-3-2018 at 09:00

Quote: Originally posted by Sulaiman  
My first thoughts;
. have you made a working, reliable small-scale battery before scaling up ?
. bromine or chlorine in large quantities is not like small scale where accidents can be survived
. I believe that if you add up the time.effort.cost of research.development.replacement.disposal
then you will consider commercially made cells..


There are no commercially made zinc bromine cells. Well, not for less than $19,000. Also, where's the fun in that? I'm not going to be reacting in gallon jugs. Obviously I plan on starting small, and it would be easier for me to set up smaller reactors with semi-automatic restocking of reagents if I really wanted to produce. Going the hydrobromic acid method will probably be the first method that I test.
Quote:
In my experience with liquid bromine, I would certainly not suggest doing that to make zinc bromide. Although it is easy to make liquid bromine in this way, doing the reaction with zinc is likely to be exothermic and due to bromine's high vapor pressure, not much of the bromine would react with the zinc.
I would urge to go the hydrobromic acid route. When you distill off the azeotropic HBr, there may be excess HBr gas coming with it. By running this over the zinc metal, you may be able to increase yield. Also, since there is water with the hydrobromic acid, it will serve to absorb a lot of the heat generated.
I am no expert though.
You may want to try a very small scale run of both methods and see which give the better yield and which is easier/more cost effective for you to do.


That's probably what I'll do. I'll buy a generic chemistry glassware set and do small scale trials of different methods to see which one will work best.

The reaction of bromine with zinc is what supplies electricity from the battery, so I suppose I could use a zinc and a carbon electrode hooked up to a beefy resistor to controllably react the two.

http://www.sciencemadness.org/talk/viewthread.php?tid=13104#...
I read that and could I just do that and then instead of adding calcium hypochlorite could I just distill off the HBr? That would mean I only need zinc, KBr, and HCl.

[Edited on 3-15-2018 by zimirken]

Sidmadra - 15-3-2018 at 13:51

Can you share more info about these Zinc Bromide batteries? I've been into the topic of DIY battery banks for a while but haven't had the time to research it.

Also I'm just going to tell you now, as an experienced chemist who knows what it's like to work with Halogens, I don't think it will be worth your effort to try to make Zinc Bromide at that scale. After your first accidental inhalation of bromine gas, $150 is going to seem cheap. The stuff is not fun to work with at all... even on a small scale. I could give you many paragraphs of warnings about working with Halogens and the accidents that could happen if things get out of hand. Screwups that happen with even experienced chemists. If you were to even attempt it at that scale, I would say that at the bare minimum you must be outside, and you must not have any neighbors near by. While you may be able to escape a giant bromine cloud, if it hits any neighbors, cops would almost certainly be called, and cops are generally very closed minded about chemistry.

With that said, $150/kg seems a bit excessive. I have a lot of experience dealing with reagents like that from China. That price sounds like either high grade Zinc Bromide (likely unnecessary for your application), or simply the bulk of the cost would be international shipping. If you were to get a somewhat larger quantity, and opt for shipping by SEA, your price would come down significant, perhaps in the range of $10-20/kg.

I put out a few inquiries about this to see what sort of prices can come back, but I just know you definitely shouldn't be paying $150/kg for that. I'll let you know what I find out.

[Edited on 15-3-2018 by Sidmadra]

zimirken - 16-3-2018 at 04:22

Quote: Originally posted by Sidmadra  
Can you share more info about these Zinc Bromide batteries? I've been into the topic of DIY battery banks for a while but haven't had the time to research it.

Also I'm just going to tell you now, as an experienced chemist who knows what it's like to work with Halogens, I don't think it will be worth your effort to try to make Zinc Bromide at that scale. After your first accidental inhalation of bromine gas, $150 is going to seem cheap. The stuff is not fun to work with at all... even on a small scale. I could give you many paragraphs of warnings about working with Halogens and the accidents that could happen if things get out of hand. Screwups that happen with even experienced chemists. If you were to even attempt it at that scale, I would say that at the bare minimum you must be outside, and you must not have any neighbors near by. While you may be able to escape a giant bromine cloud, if it hits any neighbors, cops would almost certainly be called, and cops are generally very closed minded about chemistry.

With that said, $150/kg seems a bit excessive. I have a lot of experience dealing with reagents like that from China. That price sounds like either high grade Zinc Bromide (likely unnecessary for your application), or simply the bulk of the cost would be international shipping. If you were to get a somewhat larger quantity, and opt for shipping by SEA, your price would come down significant, perhaps in the range of $10-20/kg.

I put out a few inquiries about this to see what sort of prices can come back, but I just know you definitely shouldn't be paying $150/kg for that. I'll let you know what I find out.

[Edited on 15-3-2018 by Sidmadra]


Yeah, Now that I've done more research, I'm probably going to try to stick to a hydrobromic acid method.

As far as the batteries go. There's plenty of scholarly articles on them. I've also studied all the literature on the redflow batteries. I've read a few patents on non flow versions of the battery. However, I did find one youtube video of someone who made one. https://youtu.be/qOOu-XhbfPg
It's pretty easy to make.

VSEPR_VOID - 16-3-2018 at 08:47

Hydrobromic acid is far easier to work with than liquid bromine. A reaction between bromine and zinc would be very exothermic and require on large scares an investment in a reaction vessel. In addition many methods of making bromine require HBr so you are saving yourself a step.

I would recommend the reaction of sodium/potassium bromide with sodium/potassium bisulfate. The bisulfate is available at pool stores as a pH lowering agent. It is cheap and much safer than sulfuric acid. If you did not want to do the reaction at a 100-200g scale at a time than you must find a larger distillation apparatus than those commonly used.

zimirken - 16-3-2018 at 10:10

I ordered a small chemistry glassware set that should be enough to do small batches for initial testing. If I want to scale it up, it will most likely be cheaper and easier for me to automate the process using peristaltic pumps and electronic controls and the like since that's really more of my forte. (not unsupervised of course)

VSEPR_VOID - 16-3-2018 at 13:05

Sounds good. Can we see a link to what you bought?

wg48 - 16-3-2018 at 16:19

As sodium bromide, zinc chloride and zinc bromide are soluble ethanol and sodium chloride is only slightly soluble in ethanol, perhaps a simple double displacement reaction could be used to synthesis zinc bromide from zinc chloride and sodium bromide desolved in ethanol.

clearly_not_atara - 17-3-2018 at 01:44

Zinc metal / HBr makes more sense than ZnO/HBr if it is in fact cheaper. However, ZnO should be cheaper than Zn if you buy the right grade. If you're getting high purity ZnO for sunscreen use or something I could see it being expensive.

Salt metathesis is probably not a good idea here due to the formation of complex tetrahalozincate ions which will mess with your solubility calculations. That doesn't mean it's impossible but it could certainly surprise you.

[Edited on 17-3-2018 by clearly_not_atara]

zimirken - 17-3-2018 at 04:14

https://www.aliexpress.com/item/29PCS-24-29-New-Advance-Chem...

This is the set I ordered. It's certainly smaller than it could be, but it's a good start. I'll have to do several runs to make enough product for initial testing, but the smaller initial size will allow me to learn more safely. Meanwhile, I'm relearning chemistry thanks to khan academy so I know the whys and hows instead of just the whats. I probably won't be doing anything for a while as I'm in the middle of moving, which will give me time to learn.

VSEPR_VOID - 17-3-2018 at 07:48

That looks like a good starting kit. be careful that you do not shatter that glass by heating/cooling it too quickly. I was making HBr when such a thing happened. Thank Nerd Rage, Peace be upon him, that the crack was small and the whole thing did not spill acid everywhere. It is important to have a contingency plan for if an accident happens. Have a weak base on hand to clean up spills.

AJKOER - 18-3-2018 at 04:17

First, ZnSO4 from the action of Zn on aqueous NaHSO4 and freeze out the Na2SO4 (which is also insoluble in ethanol), or the action of H2SO4 on zinc metal.

Then, try adding aqueous NaBr to the ZnSO4 and freeze out the Na2SO4.xH2O (x=7 or 10, see https://www.saltwiki.net/index.php/Sodium_sulfate_heptahydra... ).

More comments and paths see http://zinc.atomistry.com/zinc_bromide.html .

[Edited on 18-3-2018 by AJKOER]