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Rehydrating Borax

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EEYORE

Sun Oct 08 2006, 07:07PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello all,
I was wondering if it is feasible for an amateur to rehydrate Borax and convert into Sodium borohydride. When Sodium borohydride releases its hydrogen, it turns into Borax. It must be possible to "recharge" it right?Would this be something possible for an amateur with little equipment?

Matt

Marko

Sun Oct 08 2006, 07:18PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

yup, but not sure about 'amateur with little equipment' thing..

Bored Chemist

Sun Oct 08 2006, 07:50PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

A couple of things- that isn't a rehydration (which is adding water).
Secondly, I wouldn't like to have to try to get that "recharge" reaction to work even in a fully equiped lab.
Having said that it must be possible- all the boron in borohydrate was mined as borax (or some other borate) in the first place

EEYORE

Sun Oct 08 2006, 09:01PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Yea, what im getting at is that I need Sodium borohydride but I cant find it anywhere for sale excpet fuelcellstore.com which wants 15$ for 18g (jeeze is everything at their store grosely overpriced or what?) and they say it had a 25-50$ hazmat charge. That makes it really a waste of money IMHO. I read that it is recycled "one process using just water and electricity or heat". Oh well, I guess Sodium borohydride is one of those things to look forward to in 25 years.

Incase anyone is wondering what its good for, I was going to use it in a fuel cell. Platinum will cause the Sodium borohydride to release alot of hydrogen and NO CO2!!! "Cheap and relatively harmless"<-My arse!

So I wonder how it might be "recharged" using just water and electricity?

Matt

Chris

Thu Oct 19 2006, 10:32AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Sodium borohydride can be made by reacting sodium hydride with triethyl borate (4NaH + B(OC2H5)3 ==> NaBH4 + 3NaOC2H5). Sodium hydride is in turn made by reacting molten sodium metal with hydrogen gas. Triethyl borate is made by simply reacting boric acid with ethanol (H3BO3 + 3C2H5OH ==> B(OC2H5)3 + 3H2O). Trimethyl borate or other borates can be substituded just as well depending on what alcohol you start with. If you really want to start with borax, you can get said boric acid by reacting that with sulfuric acid. Starting with boric acid will be cheaper and easier though since that's readily available, and if you started with borax you would have to crystallize out sodium sulfate as a waste product.

I guess the only "difficult" part about this is obtaining said sodium metal, and getting an intert atmosphere to melt it in so hydrogen can be bubbled through from whatever source. It could be done with rather limited equipment so long as you have some inert gas and sodium. Be aware that sodium hydride is pyrophoric!! I know nothing about the rates of any of these reactions really, so start slow and use good judgement if you want to try it. Most of this stuff has to be done under argon or similar.

I could get you as much NaBH4 as you want really for quite cheaply (I'm going to be using it a lot for various borane syntheses), but only with the prerequisit that my downs cell is finished. I know that doesn't help now since it isn't and I'm in school.

Sorry. Maybe it would be economical enough for now to just buy sodium metal and do it? That might just end up being more expensive though, I don't know as I haven't bothered to run any numbers on the matter.

Anyways hope this helps.

EEYORE

Thu Oct 19 2006, 10:02PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Can you get it cheaper than $18.70 for 25grams?

Matt

Chris

Thu Oct 26 2006, 08:57PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Is that your cost for sodium borohydride?

*Boric acid is available on ebay for a total on the order of $5/lb ($0.68 for 1 mole).
*Sodium at that place I linked you will total perhaps $75lb ($15.20 for 4 moles).
*Denatured Ethanol is something like $1.50/lb ($0.07 for 3 moles).
*Assume hydrogen has a neglible cost.

All this totals about $16/mole for sodium borohydride made of those components. That translates to $0.42/g or $10.54 for 25g. There will be other costs though, just to carry out the process. Clearly sodium metal is the greatest cost if you carry out this process. It also assumes that you buy a large amount (lots of $$) of sodium (2lbs), and make a large amount of product in general. I will be making sodium borohydride many times cheaper than this when my downs cell is operational, and I could provide you with some, at some unspecified time in the future. For now though it's probably going to be $12 - $15/25g for you to make it with that relatively involved process anyway - you could have done that math, though.

It looks like if you can get it for $18.70/lb you would be ahead, because the manufacturing process I described is far more difficult than spending another $5/25g. The only other factor is that making it yourself is more fun, if you consider chemistry to be fun.

...

Thu Oct 26 2006, 11:09PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Um, he is getting it at $18 per ounce, not pound, ounce. Slight difference ;)

I am thinking that it would be cheapest to buy a little .5L lecture bottle and have it refilled that the local welding shop...

Chris

Mon Oct 30 2006, 07:28AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Yes, I am well aware of that. If you follow my calculations you will find that I listed the precursors per pound, per mole fraction used in the total synthesis, and then the final product per 25g amount. It's easy to then get the notation mixed up, which I guess I did at the end. My point is, he can buy it for $18/oz and synthesize it for like $11 plus a lot of extra effort.

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