# Why is it so much more energy intensive to compress hydrogen than methane?

Why do you need 13.8 MJ/kg (9% of energy content) to compress hydrogen to 200 bar, but only 1.4 MJ/kg (2.5% of energy content) for methane?

I looked into compressibility factors and the compressibility factor for methane is way lower than for hydrogen (up until high pressures). Does this determine how much work is required?

• The comparison to energy content seems unusual - you need energy to compress helium that has no energy content (for combustion that is). – Jon Custer May 4 at 16:56
• @JonCuster Yes, it's not useful for a comparison in general. Both gases are highly popular (with H2 as raw material for CH4) in PtX processes and this is one advantage methane has over hydrogene. So it makes sense in this specific case. – Kilian Helfenbein May 5 at 18:51

If we assume, for the sake of argument, that the compression is isothermal (constant temperature, $$T$$) the work needed to compress a sample of $$N$$ molecules of an ideal gas from pressure $$p_1$$ to pressure $$p_2$$ is
$$\text{Work}=Nk_BT \ln \left(\frac{p_2}{p_1}\right)\ \ \ \ [k_B= \text{Boltzmann's constant}]$$