Sciencemadness Discussion Board

LiOH+Al = ?

ElizabethGreene - 6-11-2014 at 05:49

Question: Will lithium hydroxide dissolve Aluminum in the same manner as Sodium Hydroxide?

(I have a fume hood capable of moving the Hydrogen safely outside.)

I'm attempting to prepare a variant of Raney Metal using LiOH instead of NaOH in the hopes that it will be slightly less pyrophoric.

Thanks!

Mesa - 6-11-2014 at 06:21

I fail to see how this would have any effect on the pyrophoric properties of the produced catalyst. Further, it's my understanding that the pyrophoricity(Is this a word?) of the catalyst is directly proportional to it's activity.


[Edited on 6-11-2014 by Mesa]

Dan Vizine - 6-11-2014 at 06:51

Nothing would surprise me re. the effects of method of preparation on final activity of a catalyst. Sometimes, the smallest change can have very profound results.

I don't, offhand, see why the LiOH leaching would give a less pyrophoric catalyst (and less active, as Mesa noted) product. But then again, this is a mysterious area and predictions are not all that reliable. Often, the only answer will be obtained by trying it in the lab. Catalysts are equal parts of science, luck & voodoo. Activity could easily be effected by residual Li ions instead of residual Na ions.

I'd like to suggest that the pyrophoricity of the "as-prepared" RaNi is not a huge issue, though. Pd/C and Pt/C are both much more easily ignited by oxygen. While I have, on occasion, seen specks of Pd/C or Pt/C ignite after being activated in the reduction process, I have never personally seen RaNi do it, however I know that it can, and has, happened.

But, as to the LiOH, even though it's the weakest saline hydroxide, it will certainly attack Al.

ElizabethGreene - 6-11-2014 at 06:57

Quote: Originally posted by Mesa  
I fail to see how this would have any effect on the pyrophoric properties of the produced catalyst.
[Edited on 6-11-2014 by Mesa]


I assumed that the spontaneous combustion of my catalyst was due to trace Sodium interacting with atmospheric moisture and igniting the hydrogen which ignites the metal.

I know experimentally that Lithium interacts with air at a much slower rate. My hope is that the slower interaction will reduce the chance of the chain reaction that ends up with me having to build a new balance tray. Again.

ElizabethGreene - 6-11-2014 at 07:03

Thank you both for your replies.

Nicodem - 6-11-2014 at 11:30

Quote: Originally posted by Dan Vizine  
I'd like to suggest that the pyrophoricity of the "as-prepared" RaNi is not a huge issue, though. Pd/C and Pt/C are both much more easily ignited by oxygen. While I have, on occasion, seen specks of Pd/C or Pt/C ignite after being activated in the reduction process, I have never personally seen RaNi do it, however I know that it can, and has, happened.

Just so that the future users of Raney Ni don't get mislead, I have to say that if you let Raney Ni dry, it will practically always catch fire. This is rarely the case with 5% Pd-C or Pt-C (though these are treacherous for causing solvent fires when you throw them in the reaction mixture without inertization - something that does not occur with Ra-Ni as this comes as a suspension in water).
Raney Ni should always be stored as a suspension in water and never left drying.
Even more dangerous is the filtration after the hydrogenation. Care must be taken to keep the catalyst moist and stop filtering as soon as the liquid goes through. The filter cake should be immediately moistened and properly disposed.
Quote: Originally posted by ElizabethGreene  
I assumed that the spontaneous combustion of my catalyst was due to trace Sodium interacting with atmospheric moisture and igniting the hydrogen which ignites the metal.

I know experimentally that Lithium interacts with air at a much slower rate. My hope is that the slower interaction will reduce the chance of the chain reaction that ends up with me having to build a new balance tray. Again.

Sodium hydroxide does not contain any metallic sodium and neither can any form in its reaction with the Al-Ni alloy. I can't imagine how you came to such thoughts.
Raney Ni is pyrophoric because of the small particle size of hydrogen saturated nickel. While the method of Raney Ni preparation has a strong impact on its catalytic activity (this has already been discussed on the forum), you cannot prevent its pyrophoricity without affecting its activity. It is better to use the proper safe handling protocols to prevent fires.

blogfast25 - 6-11-2014 at 13:49

Thanks for that clarification, Nicodem. OP's original question made little sense to me without it.

"5% Pd-C or Pt-C are treacherous for causing solvent fires when you throw them in the reaction mixture without inertization "

Please explain? In what conditions specifically can these cause solvent fires?

Dan Vizine - 7-11-2014 at 12:44

The particles can, but usually don't, catalyze the reaction of the organic vapors and oxygen in the air to the point of ignition. It depends on how far the particles waft through the air. Once wet, no problem.

I guess I was just lucky for 25 years with RaNi, or maybe never let it dry far enough. But I've seen numerous Pt and Pd catalysts cause little "glowing fireflies". In all fairness though, Pd and Pt catalysts were about 95% of what we normally used.