Hydrogen is also resourced from gases released during the processing of oil. Among these processes belong hydrocracking and hydrogenation. Hydrogen is usually diluted by gas hydrocarbon, most of all methane. The methods used to capture hydrogen are cryogenic separation, absorption or diffusion.

Cryogenic separation. The first step is to remove acidic gases (CO2, H2O) and water. The next step is, cooling the gas to -150 C at 1.4-3.5 MPa, which causes hydrocarbon condensation. The purity of hydrogen is around 90% of the volume. Since the cooling phase, it is an energetically demanding process raising the cost.

Absorption. The unwanted substances are removed from the gas by trapping them in activated carbon (CO2, CH4, N2) and zeolite molecular sieve (CO, CH4.N2). The moment the one absorbent is replete, the gas stream is led to the second absorbent, and the first regenerates by displacement of hydrocarbons.

Diffusion. The diffusion process separates hydrogen from methane and other gases using semi-permeable membranes. Hydrogen's small molecule diffuses through the membrane while other gases are captured. Membranes are made from palladium or its alloy with silver. The process takes place at 350 C and 2 MPa.[1]


[1] BLAŽEK, Josef a Vratislav RÁBL. Základy zpracování a využití ropy. 2., přepr. vyd. Praha: VŠCHT, 2006, 254 s. ISBN 80-708-0619-2