I have to produce hydrogen at a near-constant pressure inside of a really small container without using an automatic pressure release value. I would like the pressure to be relatively high, but the most important aspect is that the exact pressure needs to be predictable. I was thinking of utilizing the reaction between aluminum, water, and sodium hydroxide.

Al2O3 + 2 NaOH + 3 H2O  → 2 NaAl(OH)4
Al2O3 + 2 NaOH          → 2Na+ + 2[Al(OH)4]-

2 Al + 2 NaOH + 6 H2O   → 2Na+ + 2[Al(OH)4]- + 3 H2
2Al + 2NaOH + 2H2O      → 2NaAlO2 + 3H2.

Now, I know the pressure will slow down the reactions, but will the reactions completely stop at a certain pressure? If so, how can I deduce that specific pressure given the different concentrations of reactants and constraints of the container?

Safety is my number one priority, so I need to make sure that I can predict this pressure to a high degree of accuracy. If the pressure is too high, I won't even attempt anything. Any advice on this would be greatly appreciated.

  • 1
    $\begingroup$ The reaction is quite exothermic and it is difficult to predict the reaction rate and temperature. So it's not an easy task to predict the pressure. $\endgroup$
    – aventurin
    May 6, 2016 at 21:35
  • $\begingroup$ Yeah, I know. It can be pretty violent. I've seen reactions that went completely out of control and had to be thrown in a bath of water or an ice bucket. $\endgroup$ May 6, 2016 at 21:39
  • 3
    $\begingroup$ I would think a hydrogen gas bottle and appropriate flow and pressure control (using correctly rated components) would be the right (and safe!) way to do it. Engage a safety professional - hydrogen has a very broad explosive range in air. $\endgroup$
    – Jon Custer
    May 7, 2016 at 2:18
  • $\begingroup$ Following on from Jon's comment: maybe a hydrogen generator? If you want to control the reaction, I would stir the aluminium (powder) in water, then use a dosing pump to add, say, 6M NaOH. Use, ideally, a jacketed laboratory reactor as the reaction is very exothermic. Failing that, use a silicone oil bath as a large heat sink. What equipment are you using to hold the high pressure? I would call up to 20 bar low pressure, above 100 high and everything else inbetween medium, depending on what equipment you're used to. A matter of perspective I suppose. Also, the pressure will change with tempera $\endgroup$
    – Beerhunter
    May 7, 2016 at 10:05
  • $\begingroup$ The device has to be rediculously small. 16 cubic centimeters to be exact. Thats why I thought there wasnt enough room for the standard safety equipment. This is a very unique question haha. $\endgroup$ May 7, 2016 at 17:40


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