how much pressure does it take to turn hydrogen gas into liquid hydrogen?

Question

and would carbon desolve in liquid hyrogen to form hydro carbons?

Answer 1

The critical point of molecular hydrogen is at -239.9 degrees C and 12.9 atm. (The critical points for deuterium and tritium, isotopes of hydrogen that have masses of 2 and 3 amu instead of 1, are slightly different.)

At any temperature above -239.9C, or pressure above 12.9 atm, hydrogen is a supercritical fluid, and there is no distinctinction between the gas and liquid phases....they simply don't exist as separate phases. The first answer is therefore correct; if you pressurize hydrogen at room temperature, it will just continuously get denser (until it solidifies). In order to have a separate liquid phase, the hydrogen must be cooled below -239.9C.

Answer 2

To exist as a liquid, H2 must be pressurised and cooled to a very low temperature, 20.27 K (−423.19 °F/-252.88°C)

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Answer 3

Unless the temperature is lowered it will never turn into a liquid, it will just become more dense. Carbon will not dissolve to form hydrocarbons.