dexterrius
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Lithium hydride
hello everyone, i am thinking about buying bulk industrial grade LiH as an easy portable hydrogen source when reacted with water, the theoretical
yield of H2 is roughly 3 m3/ kg, very probably its the chemical reaction with the largest volume change - its so large that a very light baloon filled
with stoichiometrical proportions of water and LiH considering 100% conversion to LiOH and H2 should lift this baloon in air without dropping any
weight. however, the heat of reaction is still quite high what is a littlebit wasteful 
the literature says lithium should easily pick up hydrogen at 600-700°C with conversion up to 99% in an iron crucible, but i have no time to learn
this preparation for test purposes only and also i think somebody produces this stuff for a fair price and in bulk form-i mean chunks, granules, not
powder-the reaction of powder with water is too fast. could anybody help me find out from where to order LiH for a fair price???, i searched google
and alibaba but the results are not promissing. if the price would be low enough (maximum tenths of dollars/kg) i would buy some 10 kg-100kg
the dark side of the stuff: some literature says alkali metal hydrides are pyrophoric on air - it may classify this idea unpractical, but i tested
some old LiH(only 30% LiH content based on H2 volume generated, rest was already converted to Li2CO3 and LiOH) and this fine material didnt ignite on
air, also not in the test-tube at the beginning of water adition, so i hope that this kind of H2 generation could be feasible and maybe even safe
enough to avoid any unwanted ignition of the prepared hydrogen.
avaiting any response on LiH source
dexter
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bismuthate
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Do you think that LiBH4 would work? It releases more H2 by weight than LiH and you could buy NaBH4 without much trouble and use a metathesis reaction
to make LiBH4. (that is if you have a solvent)
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careysub
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Yes, lithium hydride has been used for balloon inflation systems by the military and even commercially since the early 1950s.
See attached and also:
https://books.google.com/books?id=Dk4EAAAAMBAJ&pg=PA81&a...
Could be a useful source of hydrogen gas for lab hydrogenations.
In addition it can be used for some unique chemistry.
Cheap LiH would be an interesting material.
Attachment: AD0625513.pdf (1.1MB)
This file has been downloaded 454 times
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dexterrius
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LiBH4 is a nice idea, i always thought that borohydrides naturally release diborane and hydrogen in the 1:1 ratio by water hydrolysis, so i never
calculated the hydrogen yield, wikipedia says that upon using a metal catalyst, borohydride solution gives off hydrogen, and the other product should
be the alkali borate:
"In the presence of metal catalysts, sodium borohydride releases hydrogen. Exploiting this reactivity, sodium borohydride is used in prototypes of the
direct borohydride fuel cell. The hydrogen is generated for a fuel cell by catalytic decomposition of the aqueous borohydride solution:
NaBH4 + 2 H2O → NaBO2 + 4 H2 (ΔH < 0)"
but it also says that diborane can be also formed:
"Sodium borohydride is a source of basic borate salts which can be corrosive, and hydrogen or diborane, which are both flammable. Spontaneous ignition
can result from solution of sodium borohydride in dimethylformamide"
i would not like any diborane in my H2, i would be afraid about the pyrophoricity of such mixture
but, really, LiBH4 under standard conditions should theoretically give up to 4,4 m3 H2/kg(i hope nobody will come with a reaction with even higher
volume change  ) if reacted with water, but if NaBH4 is so widely available, with
its yield of roughly 2,5 m3/kg i would be absolutelly satisfied as with a H2 source, so the question is whether it could be decomposed selectively
enough only to hydrogen an borate without or with minimal diborane release, and, again the safety and form of the product(i would prefer again bulk
against powder)
dexter
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bismuthate
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I don't think that diborane would be the biggest problem in a balloon as it will react with the water, but that still could be a problem depending
upon how you plan to use the balloon. So that's best left up to your discretion.
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deltaH
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Have you considered the reaction:
Al(s) + 3H2O(l) + NaOH(aq) => NaAl(OH)4(s) + 1.5H2(g)
It's cheap as hell and completely OTC.
Granted, it only produces 1/3 as much hydrogen as LiH on a weight basis, but still...
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careysub
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Quote: Originally posted by deltaH  | Have you considered the reaction:
Al(s) + 3H2O(l) + NaOH(aq) => NaAl(OH)4(s) + 1.5H2(g)
It's cheap as hell and completely OTC.
Granted, it only produces 1/3 as much hydrogen as LiH on a weight basis, but still... |
This should always be cheaper, even with "cheap lithium hydride".
But there might be advantages despite a higher cost.
This might be a convenient generation set-up, using an addition funnel to drip in water and achieve a controlled, incremental manner, reducing by one
the number of vessels with a caustic solution in the set-up.
Also, wouldn't the LiH, produce *dry* hydrogen? Water reacts with the LiH to make LiOH, and both NaOH and KOH are used as efficient drying agents. The
reaction product would scavenge up any extra water.
Perhaps a "redneck" hydrogenator system could be devised using an iron pipe, a test tube of reaction mixture to be hydrogenated, and a not-gas-tight
container of LiH, or something similar. Add a pre-weighed piece of ice to the LiH, drop it into the pipe, insert the test tube, flush with argon, and
screw on the cap. You would need to work out the correct amounts to get a fairly predictable pressure. Maybe a low fusible allow plug could be used as
a replaceable pressure release at the end.
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zed
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Well, some used hydrogen generated from LiH, but CaH2 probably does a better job, and it is easier to handle. It also used to be cheap as dirt,
on-line. Not so any longer.
It was used as part of a weather balloon/ radio transmitter system. Military surplus stuff.
Could make your own, via the hydrogenation of Calcium Carbide. Seems do-able. And, economical.
https://www.jstage.jst.go.jp/article/jinstmet1952/58/3/58_3_...
There is a PDF of the Paper, available on site.
Somewhere on this board there is a link to a pretty good paper/patent on the topic.
This is actually very old information. Dig.
http://www.ebay.com/itm/Calcium-carbide-2-pound-mole-root-vo...
Probably cheaper somewhere.
[Edited on 20-12-2015 by zed]
[Edited on 20-12-2015 by zed]
[Edited on 20-12-2015 by zed]
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careysub
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It depends on the relative cheapness of hypothetical "cheap LiH" or "cheap CaH2" neither of which we currently have any actual sources for.
Regarding making CaH2, looking at the conditions for formation (at a low rate apparently) if you already have a source of dry H2 and equipment to
perform a 165 psi hydrogenation, you don't need the hydride as a hydrogen source in the first place.
The cheapest source I know of for CaC2 in the U.S. is Karst Sports, if you want 10 lb ($95). About the same price as the German carbide when its
shipping is included.
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dexterrius
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here is some info about hydrogen generation from NaBH4 - looks nice, the heat released is only half of that compared to LiH per unit of hydrogen and
five times less compared to Al + NaOH + H2O (thats the reason why i am looking for other source)
https://www.youtube.com/watch?v=t0TSRDYJOgI
in the attachment you can find some info about the catalyst
Attachment: Kopra_Christopher_2008 (1).doc (35kB)
This file has been downloaded 1462 times
dexter
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zed
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I'm a big fan of Sodium Borohydride. It simply hasn't reached the price levels once projected.
It is kind of expensive. And not really easy to make at home. Nice clean source of hydrogen. But, it chokes my budget.
Been a lot of work done on trying to develop systems for regenerating spent NaBH4, and reusing it. In other words, rechargeable systems. No big
winners yet.
Also been a lot of work done creating complex hydrides, via Ball Milling exotic ingredients together. Folks still haven't hit the sweet spot......a
material that releases hydrogen readily, and reabsorbs it just as readily, under reasonable conditions.
Change the course of our civilization, if somebody hits a dinger out of the park on this one.
Cheap Calcium Hydride does occasionally surface, but it is ephemeral. Here today, gone tomorrow. Just a few years ago, it was often available as
surplus, for ~$15.00 per kilo.
http://www.ebay.com/itm/US-Signal-Corps-sealed-CALCIUM-HYDRI...
[Edited on 21-12-2015 by zed]
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careysub
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BTW - I wonder if everyone caught the advertised purpose of that cheap German calcium carbide?
"mole, root vole expeller"
As in - you pour a mixture of carbide and water into the burrowing rodent hole, then after applying a long handled match to the burrow, the rodent is
expelled out the other end.
Those Germans and their creative uses of chemistry.
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deltaH
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Launched into orbit is more like it
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zed
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Anyhoo. That can of CaH2 went for a reasonable price. http://www.ebay.com/itm/US-Signal-Corps-sealed-CALCIUM-HYDRI...
Me some too. I'll take a case load.
As fer voles, moles, and gophers....There is something to be said for putting a small block of dry-ice into the hole. It vaporizes, flows down and
fills, the mole hole, with CO2, whereupon the pesky rodent goes to sleep permanently.
Though I gotta admit, charging the hole with Acetylene and detonating, does sound very interesting.
[Edited on 27-12-2015 by zed]
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dermolotov
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| Quote: Originally posted by deltaH | Al(s) + 3H2O(l) + NaOH(aq) => NaAl(OH)4(s) + 1.5H2(g)
Granted, it only produces 1/3 as much hydrogen as LiH on a weight basis, but still... |
This is what I do. Sometimes HCl + Zn.
I prefer to use the HCl + metal because depending on the metal, I can control the rate of bubbling. With a tweaked concentration of HCl and Iron
shavings, one could theoretically continuously generate hydrogen gas for a week.
Alkali Metal Hydrides are a great in-situ hydrogen source. But then again, so is Ammonium Formate which should be cheaper.
Remember that during a gas generation, sealed atmosphere, one must use a pressure equalising funnel. I've had so many mishaps with simple addition
funnels, hehe 
www.alchemylabsupply.com/
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AJKOER
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Hydrogen while a very light gas, has a few down sides.
First, it loves to escape. Also, if you let's some in a room, be wary as it has a large range where H2 mixed with air plus a spark (from say a light
switch) will cause the room to explode! See https://en.m.wikipedia.org/wiki/Flammability_limit
There are other options that you may have missed! See https://en.m.wikipedia.org/wiki/Lifting_gas
Interestingly, you may be able to use a combination approach.
[Edit] A not so original idea (see http://www.engadget.com/2015/08/07/solar-powered-hot-air-bal... ) is to use the sun to heat your lifting gas. I was thinking of using one of those
Aluminum covering from an emergency blanket, adding a light frame, forming a concave mirror to use sunlight to heat a black balloon from which the
'mirror' is suspended.
[Edited on 28-12-2015 by AJKOER]
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careysub
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| Quote: Originally posted by dermolotov | ...
Alkali Metal Hydrides are a great in-situ hydrogen source. But then again, so is Ammonium Formate which should be cheaper.
... |
What is the procedure for generating hydrogen gas from ammonium formate?
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dexterrius
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so finally i got some NaBH4 and made tests with it, in agueous solution it decays fast at low pH and just very slowly at basic conditions, if just
water is added it quickly goes alkaline due to the decomposition and the formed borate and it slowly releases a steady stream of H2, the complete
decomposition can take several days. if heat is applied the reaction accelerates exponentialy but in the 1 gram scale (as i tested) it is not a
runaway reaction and if the external heating is cut off , it cools down and slows down again. i suppose that upon upscaling the size of the experiment
the heat transfer trough the walls of the beaker can get weak enough that you get a quick thermally self sustaining reaction at some equilibrium
temperature when the water evaporation cooling(of course the hydrogen will be very moist at high temperatures) is equal to the reaction heat. but if
the reaction speed - temperature dependence curve rises less steeply than the water vapour pressure - temperature dependence curve, it will never get
self sustaining at higher temperatures(and resulting reasonable reaction speeds) without external heating. i didnt test this.
next i tested the catalysed decomposition in the presence of cobalt acetate, upon adition of which to the NaBH4 solution a black powder forms (should
be some cobalt boride) and the reaction goes several times faster, but not fast enough for instant hydrogen generation (the reaction is very fast when
the cobalt acetate enters the solution but after the initial few second boom it ceases to an order slower rate-however still higher than the
uncatalyzed decomposition)
so finally i tested decomposition with HCl (as some literature states):
HCl + NaBH4 + 3 H2O = H3BO3 + NaCl + 4 H2
the weight ratio of the HCl and NaBH4 is roughly 1:1, the reaction is very fast and quantitative, even too fast to handle(went to completion in
seconds) so i pressed (hand pressing or hammering in a pipe does not make tablets stiff enough) the NaBH4 grains to larger tablets using a laboratory
press (roughly 1 - 2 cm average size) and those reacted completely in some 30 second time scale with 3% HCl solution (it need to be diluted to this
extent to avoid boiling off too much water by the generated heat - the end temperature of the reaction mixture was only around 50-60°C), i didnt
notice the presence of any borane gas (smell), so it must react with water very quickly. so finally i am satisfied with a really quick easily
upscaleble hydrogen source, unfortunatelly the price of NaBH4 is too high to use it for this purpose(the lowest price offer i got was 50 dollars/kg if
ordered in 25kg quantity - can anyone get it for a lower price?), and making the tabets is quite laborous and time consuming(until you dont have
access to a large industrial press)
dexter
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Mesa
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Finely divided palladium metal(Pd/C etc.) suspended in aqueous solution of the formate results in decomposition to H2, CO2, and NH3 via catalysis.
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JJay
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You can generate alkali metal hydrides in the lab by directly combining alkali metal with hydrogen at high temperatures (around 700 C) at slight
pressure. Pressure isn't really necessary but does keep air out of the apparatus and speeds the reaction. Bauer's two-volume handbook in the
Sciencemadness library gives some details.
[Edited on 9-1-2016 by JJay]
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Heavy Walter
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There is a new Hydrogen storage device -an hydride cell based in TiMn alloy- able to delivery 10 liters of Hydrogen PTN.
Seems useful for the small lab, avoiding pressurized cylinders or chemical reactions for H generation.
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semesa
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| Quote: Originally posted by JJay | You can generate alkali metal hydrides in the lab by directly combining alkali metal with hydrogen at high temperatures (around 700 C) at slight
pressure. Pressure isn't really necessary but does keep air out of the apparatus and speeds the reaction. Bauer's two-volume handbook in the
Sciencemadness library gives some details.
[Edited on 9-1-2016 by JJay] |
Have you ever tried this?
It's exceptionally important that everything be done strictly air-free. The hydrides generated are pyrophoric and in a drum full of hydrogen gas
being heated to 600*C+.
Around here they call that a bomb.
There was some ideas going around a while back using diborane and an organoaluminium compound, I came across some cool studies earilier today where
they were making phosphine and silyl coordination complexes with tungsten(VI) directly from simple metal phosphide/sillicides.
I coincidentally have a few hundred grams of slightly impure (VI)Hexachloride/oxychlorides going to waste.
[Edited on 10-1-2016 by semesa]
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JJay
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I have not.... You could use a bomb reactor, but a tube furnace with a stream of hydrogen through it seems easier to construct.
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