# Limit the production of hydrogen in a small container

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.

• 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. May 6, 2016 at 21:35
• 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. May 6, 2016 at 21:39
• 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. May 7, 2016 at 2:18
• 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 May 7, 2016 at 10:05
• 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. May 7, 2016 at 17:40