LiH Production Apparatus Design and Operation

this crudely drawn apparatus is meant to produce hydrogen (from the left) and then cool the hydrogen and dry it then heat the hydrogen again and pass it over scored/cleaned lithium metal in a reaction vessel.

before the reaction takes place the vessel is purged with hydrogen.



part - 1 - Hydrogen

The hydrogen is produce from the reaction between water and aluminium and is catalyzed by NaOh. In trials, i was able to successfully produce hydrogen for up to 3 hours with no sign of slowing in a 1 litre reactor after 3 hours the hydrogen production began to slow significantly but i believe this is because of over-saturation of aluminium hydroxide in the water and not so much because of a decrease in catalytic activity from the NaOH.

part - 2 - Drying the Hydrogen

The reaction between the aluminium and the water is quite exothermic with higher quantities of NaOH especially (otherwise though, not enough h2 is produced) and because of this there is an exess of moisture in the vapors coming from the reaction vessel (not to mention very fine particles that are carried by this moisture/vapor). in order to dry the hydrogen and prepare it for reaction with the lithium (as moisture will react with the lithium) it is first directed through a vigreaux/air cooled collumn (to keep as much water in reactor as possible) and then through a distillation adapter and into a coil-type condenser that has been cooled by ice cold water. more moisture is condensed here and is collected in a water trap. after the water trap the vapors travel onwards out through a vaccuum adapter and into stainless steel tubing.

part - 3 - Further Drying the Hydrogen

the stainless steel tubing directs the hydrogen into a trap filled with (currently h2so4. but this is probably not a good idea as if it successfully traps h2o it should release SO2 ??) this is only a precautionary step though as the hydrogen seems to be dry enough already. This step needs to be improved. i need something to dry the h2 and preferably also remove any residual O2 if possible.

part - 4 - Heating the Hydrogen

in this step the tube that the hydrogen is in is heated just before a thermostat. the hydrogen is heated to 200C

part - 5 - Reaction

the hydrogen is reacted with lithium to produce lithium hydride (in a stainless steel reactor that has a top that has an inlet and an outlet and a bottom that comes off)

note: the lithium is scraped on the surface to expose fresh lithium just before reaction.

note 2: in the first experiment the hydrogen was not heated as i am worried about the moisture level of my hydrogen. The reaction was mostly a failure as the lithium was only barely scratched before the reaction but where it WAS scratched was covered with a powder that was easily distinguished from the oxide/nitride/etc layer that normally forms.

note 3: the lithium might need to be cleaned while covered by diethyl ether and then dried by the heated hydrogen for best reactivity. but i am hoping that this is not the case. any info on the reactivity of hydrogen and lithium would be appreciated. im sure its out there. but i havnt looked hard enough i suppose ill keep looking though.

Question: how can i dry my hydrogen.

Question 2: moisture seems to be the biggest danger in this experiment and i am confident that the moisture level is really low after the coil condenser already. this being said, would a more experienced person be brave enough to raise the temperature of the hydrogen to say 180C - 200C and attempt to react the hydrogen more quickly/efficiently?

if success happens: i plan to keep it in the reaction chamber (for only a few minutes) under hydrogen and then either attempt to dissolve it slowly in anhydrous ether mixed with aluminium chloride (for storage in the form of LAH) or dispose of it as i am truly afraid of chemicals that can ignite so easily. even if it's not likely.

in the future: if i am successful i hope to share my findings and experiment to find reliable methods for hydride production so that others may benefit.





coil condenser shown below


[Edited on 19-2-2018 by 5Qr25Pla]

[Edited on 19-2-2018 by 5Qr25Pla]

An excellent pre-write up, good luck when it comes to carrying out the procedure, certainly not something I’m willing to try at this stage. For drying the hydrogen gas, pass it through a drying tube packed with desiccant: gas generator -> rubber tubing -> bung with glass tube -> drying tube -> reaction vessel (see image for example). From what I understand, hydrogen gas and concentrated sulphuric acid shouldn’t react so bubbling it through is a good way to remove moisture.

Just to clear up a misconception, NaOH doesn’t act as a catalyst as it is consumed by the reaction, producing sodium aluminate and hydrogen. 2 NaOH + 2 Al + 2 H2O -> 2 NaAlO2 + 3 H2.

@LearnedAmateur
thank you, that image was very helpful. and knowing that the sodium is used up in the reaction makes me wonder if it would be better to put more sodium.

@wg48 already mentioned that an addition funnel for adding more liquid/naoh mixture would let me add more liquid over time without letting other gases in. so i added an addition funnel to the apparatus. this should clear up the problem of gas production slowing down.

@Magpie
i couldnt get my hands on a copy. is it in the library this site has by chance? or someone else's maybe?



My main concern here is how reactive/volatile/powerful the reaction between the lithium and hydrogen when i increase the heat. knowing what the worst case scenario is would be very helpful. the amount to be processed is 1 gram or less.

the apparatus will be purged by produced hydrogen before any lithium is introduced to the reaction vessel. this should eliminate all possibility of flashback if something goes bad. potential pockets of oxygen/nitrogen/etc... will be eliminated in final build of apparatus.

other info: the heat is supplied by NiCr coil + blower + potentiometer + thermostat at end of blower to ensure heat doesnt exceed 392F/200C (supposed autoignition temperature of Lithium Hydride according to https://cameochemicals.noaa.gov/chemical/996.

Quote: Originally posted by 5Qr25Pla

... knowing that the sodium is used up in the reaction makes me wonder if it would be better to put more sodium.

How did you come up with this as worst case? You are not using O2, but air for an environment.

Quote: Originally posted by Bert

Quote: The explosion produced by 90% Hydrogen 10% Oxygen (worst case scenario. Less than 1% oxygen is expected) doesnt seem to produce much force. This sounds crazy. But in a glass bottle it did not burst the bottle upon ignition. How did you come up with this as worst case? You are not using O2, but air for an environment.

i dont think i have been clear enough i am sorry. let me clarify.

the ENTIRE apparatus (including lithium reaction chamber, exhuast and heating tube) is PURGED with hydrogen or argon (hydrogen in my current case) prior to initiation. when the apparatus has been purged with (roughly 3 litres @ 1atmosphere) enough hydrogen/argon then the lithium is placed in the reaction vessel with the hydrogen still running. when the lithium is in the reaction vessel another 0.5 - 1.0 litres of hydrogen are used to purge the (TINY) reaction vessel. once the lithium has been introduced and the hydrogen has purged the system, then and ONLY then is heating to begin. the heating is done by the hydrogen itself so as to avoid hotspots on the lithium and to increase the reactivity of the hydrogen.

the picture that you @Bert provided was useful to me though. if the vessels have been purged properly (and there are no air pockets available for other gases to dwell in) then there should be relatively no risk of fire/explosion during NORMAL operation (ASSUMING NO LiOH/Lixx is present. but. as there will almost for sure be LiOH/Lixx present there is still the very small chance that the reaction produced between the Li, Lixxx, LiH, H2, and any produced gases could create small, localized, explosions.

these "explosions" should be relatively harmless actually as long as the Lixx % is kept very low (preferably at < 0.05 grams total impurity or less) and the reaction is kept slow/low temp.

the reaction doesnt need to yield %100. and even at room temperature the yield should be "enough"

the added heating is PRIMARILY used to greatly reduce the reaction time (allowing the reaction to complete before the hydrogen stops being produced) but making the yield a higher percentage is also a very nice benefit. this will also help to keep the LiH from getting trapped in unreacted lithium.


i have ran the apparatus with very slight success. but with no heating. i am afraid that when the reaction really gets going it will be unstoppable due to the heat that it generates. a good example of a reaction that gets going and then heats itself and continues to heat itself is the reaction of methanol over a red-hot catalyst. the methanol goes over the catalyst and then reacts with minute levels of oxygen and produces formaldehyde. the reaction is so hot that it will sustain itself as long as the gases are pushed across the catalyst. if this happens with my LiH reaction that is fine. but i dont want my reaction to superheat itself to above about 200C. i want to stay as close to the bare minimum total energy as possible.

Quote: Originally posted by Magpie

"Small-Scale Synthesis of Laboratory Reagents" by Leonid Lerner

Everytime I see Magpie's sig, "The single most important condition for a successful synthesis is good mixing - Nicodem", I think of len1's disgraceful failure and the subsequent arrogant attacks on Pok, and others, in the potassium sticky thread... I know you miss him, Mag, but I don't.

Quote: Originally posted by Bert

Non functioning link. Copyrighted work by a member. Book costs about US $170 to buy.

The link is now fixed.

I am a great fan of Len1's work, but as far as I am aware, he has NO rights to that book. They were all signed over to the publisher.

It was a labour of love and now we have it.
(And so we should, there are even a cluster of chapters in PrePub)

Also,there are a number of threads here about the book and there already is a link in References forum.

Enjoy




/CJ

[EDIT] - Post above was posted while I was writing this

[EDIT2] - Stupid grammar

[Edited on 22-2-2018 by Corrosive Joeseph]

[Edited on 22-2-2018 by Corrosive Joeseph]

Quote: Originally posted by Corrosive Joeseph

I am a great fan of Len1's work, but as far as I am aware, he has NO rights to that book. They were all signed over to the publisher. It was a labour of love and now we have it. (And so we should, there are even a cluster of chapters in PrePub) Also,there are a number of threads here about the book and there already is a link in References forum.

Quote: Originally posted by Bert

Somehow I missed whatever controversy happened. Before I was a moderator?

Quote: Originally posted by Bert

Somehow I missed whatever controversy happened. Before I was a moderator?

Improvements

The Verdict

okay. the hydrogen is ready and waiting. and our (hopefully sealed very very well because if its not thats gonna be really bad) reactor is mostly assembled and ready to go. now on to the actual reaction.

DO NOT WORK WITH HYDROGEN WITHOUT GREAT VENTILATION

before we begin we should be sure that we are ready to either store or dispose of the product. the product lithium hydride will be in lump metallic form. it will be stuck to the insides of the apparatus and it will be difficult to remove without a drill or mill or something. a hammer and chisel will work. but be aware that the product is dangerous and CAN ignite if care is not taken.

the hydride is mostly safe in the air and as long as one is careful it can be removed without any inert atmosphere or special solvents.

do NOT allow moisture to come into contact with the hydride.


the reaction has three main parts

1. the hydrogen is released from its storage tank
2. the hydrogen is dried over very cold sulfuric acid or better drying agent
3. the hydrogen is reacted with the lithium in the final reactor

the lithium reactor (1inch x 8-12 inch nipple/pipe) is filled with up to 10 grams of lithium (i used 3 grams and it seemed to be a small amount that was hard to get out as most of it coated the walls. more would likely pool up easier)

the other cap from before is placed on the end of the pipe and tighted to the extreme. (when you close up the exhaust and spray hydrogen in there should be ZERO leaks. ZERO)

leaks can fairly safely be found with a flame. if there is a dangerous amount of leakage a flame will be present. if there is a flame. just turn off the hydrogen. allow to cool. and tighten again.


once the reactor is sealed and the lithium is inside be sure that the drying cylinder and all connections are good. then purge the system with hydrogen to remove air.

after purging the system and you are sure there is no more air you may begin heating the lithium reactor.

heat the reactor slowly to between 700C and750C (the book by Len1 suggested 730C)

at this temperature the lithium AND the lithium hydride are both liquids and the reaction goes pretty easy. as long as the temperature is accurately measured and hydrogen flow is adequate about 4-8 grams per hour can be converted to the hydride.

the lithium hydride will form blobs on top of the lithium that will sink to the bottom and expose more lithium. eventually (rather quickly) all of the lithium is converted and hydrogen absorbtion stops.

once hydrogen absorbtion stops allow the reactor to cool completely while under hydrogen still (doesnt take long. few minutes tops)

once cooled you may disassemble your device and retrieve the hydride. unscrewing the bottom cap to get to the hydride was the route i took. but this was VERY difficult. its worthwhile. but if you want to make larger amounts i would recommend coming up with a method to quickly get the cap off. the lithium melts and "welds" to the inside of the cap and tube making removal of the cap very difficult and i even admit that i was tempted to just cut the end off. but i didnt. after much work i got the cap off.


lithium WILL eventually make its way through the metal and the threads on the cap. but this never happened to me. i wouldnt run this reaction for longer than an hour or two. just to be safe. another good idea would be to put the reactor in another steel tube just in case lithium leaks. but as long as you have good ventilation the leaking lithium shouldnt be too big of a worry. it will come out very slowly. just stop the reaction if it does.




about 4 hours of work and about 3 or 4 grams of lithium yielded about 3 grams of lithium hydride. there was more hydride stuck inside that i left there and couldnt easily remove.


any impurities from the oxidation/nitration of the lithium were negligable and did not seem to hurt the yield to any noticable degree.