NOVELTY - The conversion of hydrocarbon gas into hydrocarbon liquids for generating synthesis gas (17) by fischer-tropsch process, comprises converting hydrocarbon gas into synthesis gas, producing synthesis gas, and reducing chains of hydrocarbon liquid intermediate in hydrocracking unit by a gas rich in hydrogen. The hydrocarbon liquid intermediate and a residue gas (3) comprises hydrogen. The gas rich in hydrogen is produced by a purification process of flow hydrogen, which is compressed before used for the reduction of the chain of hydrocarbon liquid intermediate.    USE - Used for generating synthesis gas by fischer-tropsch process.    ADVANTAGE - The process avoids the loss of hydrogen and is cost effective.    DETAILED DESCRIPTION - The conversion of hydrocarbon gas into hydrocarbon liquids for generating synthesis gas (17) by fischer-tropsch process, comprises converting hydrocarbon gas into synthesis gas, producing synthesis gas, and reducing hydrocarbon liquids intermediate chains in hydrocracking unit by a gas rich in hydrogen. The hydrocarbon liquids intermediate and a residue gas (3) comprises hydrogen. The gas rich in hydrogen is produced by a purification process of flow hydrogen, which is compressed before used for the reduction of the chain of hydrocarbon liquid intermediate. The residue gas resulting from the fischer-tropsch process recovers, treats and adjusts with a pressure in an adsorption unit of modulated gas supplied by a hydrogen effluent gas (14) resulting from a methane reforming unit to a vapor, which is placed in contact with an adsorber bed. At first exit, the gas rich in hydrogen has a concentration of hydrogen (70 vol.%) that is higher than that of the hydrogen effluent gas. A residual flow (10) is placed at a second exit. The adsorption unit of modulated gas is associated with an integrated compressor. Each adsorber unit and a modulation cycle of pressure comprises phases of adsorption, decompression and purging. The gas recycles from adsorption unit of modulated gas to absorb a different compound from hydrogen and to produce the adsorber bed of the gas rich in hydrogen. At the decompression phase the residual flow of pressure swing adsorption is produced and at the purging phase, a purging gas is produced. The recycle gas of pressure swing adsorption (7) is residual flow/purging gases compressed with the pressure.    DESCRIPTION OF DRAWING(S) - The diagram shows the conversion of hydrocarbon gas into hydrocarbon liquids:    Residue gas; (3)    Pressure swing adsorption unit; (7)    Residual flow; (10)    Effluent gas; (14)    Synthesis gas. (17)