TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process Details : The main impurities in the gas comprise N2, CO, CO2 and methane. The proportions are 35% min. N2, 10 - 20% CO and at leas one impurity from CO2 and CH4, the sum of the contents of H2, N2 and CO making up at least 90% of the gas volume. The primary adsorbent, comprising an active carbon, adsorbs the impurities CO2 and CH4, and the second adsorbent, the Li-exchanged faujasite zeolite, adsorbs mainly CO and N2. The gas may also contain water vapor, which is eliminated by a third adsorbent up-stream of the first and second adsorbents, comprising alumina or activated alumina. The gas may be derived from a catalysed partial oxidation process. The adsorption is operated at a pressure less than 10 bars, more preferably 4 - 8 bars, and the adsorbent is regenerated at less than 3 bars, more preferably less than 1.5 bars. The temperature of the H2-depleted gas is 20 - 50degreesC. The flow rate of the gas is less than 1000Nm3/h, more preferably less than 300 Nm3/h. The second adsorbent comprises a zeolite X with a Si / Al ratio of 1 - 1.25, more preferably 1, more than 80% exchanged by Li ions(more preferably greater than 94% exchanged), also containing residual cations K, Na and/or Ca. The recovered H2-enriched gas contains more than 97% H2, more preferably greater than 995 and especially greater than 99.999%. The preferred gas mixtures purified by the process contain 15 - 38% H2M 40 - 75% N2, 10 - 205 CO, 0.1 - 5% CO2, 0.1 - 5% CH4 and water vapor. EXAMPLE - Trials were effected with a pilot plant enabling the effecting of cycles of pressure equilibration By definition, PSA yield signified the ratio of quantity of H2 produced to quantity of H2 in the original mixture ; and productivity, the quantity of gas treated per unit of vol. of adsorbent(pressure normalized). Comparative trials were effected at 10 bars adsorption pressure, 1.6 bars regeneration pressure and at a temperature of 40degreesC. The adsorbent bed was formed of a layer of carbon and a layer of zeolite. A comparative trial(1) was carried out using a type 5A zeolite and a trial (2) using a type X zeolite 95% exchanged with Li with Si / Al = 1(LiLSX) The flow rate of the gas to be treated was 12 - 17 Nl/min, and the composition was 33% H2, 2% CO2, 16% CO, 2% CH4 and 47% N2. Trial 1 : Yield = 63% ; productivity = 1.37 Nm3/m3/bar ; Trial 2 : Yield = 68% ; productivity = 1.62 Nm3/m3/bar.