# Methane storage

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28 minutes ago, Moreno said:

Maybe you may make calculation for methane in particular? For example, if we fill some cylinder with LNG and will wait when temperature of LNG will become equal to room temperature. How much pressure on cylinder walls it will exert now?

You need to provide the specifics of the container. I picked an easy value, but all it is is P1V1 = P2V2 and we know what P2 and V2 are: 1 atmosphere  and 22.4 L at 0 ºC and then correct for the temperature (going from 273K to 293K is only ~ 7.3% change)

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3 hours ago, swansont said:

You need to provide the specifics of the container. I picked an easy value, but all it is is P1V1 = P2V2 and we know what P2 and V2 are: 1 atmosphere  and 22.4 L at 0 ºC and then correct for the temperature (going from 273K to 293K is only ~ 7.3% change)

Where did you take it from? When LNG reaches room temperature, I think it's closer to -167 C to +25 C change. Where did you take 0 C from? I think container could have around 50 L volume. Let say initially it was completely filled with LNG. How much pressure will grow, when its content will reach +25 C? What pressure the cylinder walls will experience?

Edited by Moreno

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12 hours ago, swansont said:

That should approximate what would happen for a non-ideal gas.

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4 hours ago, Moreno said:

Where did you take it from? When LNG reaches room temperature, I think it's closer to -167 C to +25 C change. Where did you take 0 C from? I think container could have around 50 L volume. Let say initially it was completely filled with LNG. How much pressure will grow, when its content will reach +25 C? What pressure the cylinder walls will experience?

You didn’t ask about the pressure while it’s liquid, you asked about the pressure at room temp.

0 C comes from STP.

36 minutes ago, John Cuthber said:

Better than the one you’ve offered, though.

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20 hours ago, swansont said:

Better than the one you’ve offered, though.

Fair point.
OK imagine I fill a tank with liquid methane at its normal boiling point.

The density is 0.656 kg/litre

And if I close the tank and let it warm up then (ignoring the deformation of the tank)  the density will stay the same, so I need to find the pressure where gaseous (strictly, supercritical) methane has that density at room temperature- say 20C or 293K.
I spent a while trying to find data for that, but I couldn't. I will have a look when I get  back to work, to see if anyone has the data.

On the other hand, if I use pv=nrt well, p=nrt/v

I have chosen v= 1 litre

the mass is 656g

That's 41 moles so n = 41

r = 0.0813 litre bar / k/mol

About 950 Bar (I think- feel free to check).

However, fundamentally, the reason I said it was a way of estimating the pressure badly is that you are using the ideal gas laws- which assume that the compressibility of a gasi is quite large.

However, you are actually considering a supercritical fluid.

Gases are easy to compress because they are mainly empty space.

That's not the case with supercritical fluids where the molecules are nearly "in contact" with one another. If the molecules are "in contact" then you have a liquid

In the case of liquids, the compressibility is tiny- for most  practical purposes water is regarded as incompressible, for example.

So, to get the 656 g of supercritical fluid which (near the critical point) has a density of 0.562 kg/l into a 1 litre tank you need to compress it by a factor of about 85%.

Now, I know it's not the same thing, but to compress water to that extent the pressure needed is huge.

The compressibility is about 0.5% per 100 Bar

And you are trying to compress it by about 15%
That's about 3000 bar.

Methane is going to be about the same ballpark.

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