Ultra-High-pressure hydrogen storage?

[MatterBeam]

Hi!

Super-carbon materials with extreme tensile strengths allows for tanks to withstand very high pressures.

Chilled hydrogen gas at high pressures (700 atm) can reach densities equivalent to liquid hydrogen.

If we could compress the hydrogen further, could we reach hydrogen densities higher than simple liquid hydrogen?

What is the maximum pressure that a tank made out of carbon nanotubes can withstand?

So, at a pressure near the limits of the performance of super-carbons, what hydrogen density can we get?

[steve_v]

6 minutes ago, MatterBeam said:

If we could compress the hydrogen further, could we reach hydrogen densities higher than simple liquid hydrogen?

Well, some guys recon you can make metallic hydrogen with diamond anvils, somewhere around 500Gpa. I'm waiting for some confirmation though.
Good luck with a tank material for that kind of pressure...

Edited April 22, 2017 by steve_v

[MatterBeam]

1 hour ago, steve_v said:

Well, some guys recon you can make metallic hydrogen with diamond anvils, somewhere around 500Gpa. I'm waiting for some confirmation though.
Good luck with a tank material for that kind of pressure...

Understood.
What what about working the other way around: finding the maximum tank pressure a material can hold?

[peadar1987]

3 minutes ago, MatterBeam said:

Understood.
What what about working the other way around: finding the maximum tank pressure a material can hold?

Well that depends on the tank size. Hoop stress is given by P*r/2t, where P is the internal pressure, r is the tank radius, and t is the wall thickness. If you set the hoop stress to the tensile strength of you material you can work out a relationship beteen the radius and the thickness for a given internal pressure.

[MatterBeam]

2 minutes ago, peadar1987 said:

Well that depends on the tank size. Hoop stress is given by P*r/2t, where P is the internal pressure, r is the tank radius, and t is the wall thickness. If you set the hoop stress to the tensile strength of you material you can work out a relationship beteen the radius and the thickness for a given internal pressure.

Well, if we set hoop stress to 5.8GPa (Zylon's tensile strength), P the hydrogen pressure, and have r/2t the variable, I can work out some stuff.
We want to maximize the pressure but minimize the mass. Overall, we want the maximum mass ratio for the tank.

A few excel tables later, I get: https://docs.google.com/spreadsheets/d/1kbxzPTB-eqJMTytXSQei22H6sHF_-RwdA5kvpKO10zA/edit?usp=sharing

Points of interest:
-Tank mass ratio is independent of radius and wall thickness, only tensile strength counts
-I used 90K temperature, which means liquid oxygen can be kept as coolant. 
-Ideal gas law gives 2.668kg of hydrogen per pascal per cubic meter at 90K.

With A-36 Steel, mass ratio is 0.63
With Zylon, mass ratio is 6.27.
With monocristalline silicon, mass ratio is 8.12
With carbon nanotubes, mass ratio is 73.
With graphene...... mass ratio is an incredible 150.

Thoughts on this method?

[sevenperforce]

1 hour ago, MatterBeam said:

With A-36 Steel, mass ratio is 0.63
With Zylon, mass ratio is 6.27.
With monocristalline silicon, mass ratio is 8.12
With carbon nanotubes, mass ratio is 73.
With graphene...... mass ratio is an incredible 150.

Thoughts on this method?

About what I expected.

If we could make a tank out of woven carbon nanotubes or straight-up graphene, then yes, high-pressure GH₂ would be the way to go. But we can't...not yet, anyway. So until then, we're stuck with liquid hydrogen.

[mikegarrison]

Also remember that hydrogen is literally the smallest atom. So it leaks into and through most other materials. Plus, it's quite reactive. So it can damage the tanks that it is contained in. And the more pressure inside, the more it will want to leak. So you have to consider the permeability and chemical susceptibility of the tank material.

[K^2]

Hydrogen won't follow ideal gas laws at high pressure. It's a notoriously difficult substance to compress. Basically, don't count on density going up much above 0.1g/cm³.

[p1t1o]

Im not sure if there is even a difference between hydrogen gas at liquid density and liquid hydrogen, and since liquid hydrogen remains liquid hydrogen at extreme pressures (I'll assume that theoretical metallic hydrogen is out-of-scope for mere storage) Im gonna say no.

[Zeiss Ikon]

Permeability was mentioned above.  Recall that graphene(s) are basically chicken wire made from carbon -- there's a hole in each hexagon big enough to pass, not just hydrogen, but water molecules (it's been proposed as an osmotic filter with  no modifications).  So, you have to come up with a way to plug the holes, else your hydrogen will permeate the graphene (and this is almost certainly bad for graphene, as thermal energy will tend to allow conversion into various chain lengths of alkane hydrocarbons -- i.e. your tank liner will tend to "magically" transform into gasoline or kerosene).

[sevenperforce]

On 4/22/2017 at 11:45 PM, mikegarrison said:

And the more pressure inside, the more it will want to leak.

This is the key element.

[p1t1o]

45 minutes ago, sevenperforce said:

element.

ho-HO! I see what you did there

SCIENCE JOKE!!