TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Reactor: The reactor contains a catalyst for converting hydrocarbons to H2, which preferably is in or directly on the diffusion membrane. In particular, the membrane is autocatalytic. The membrane is heated, preferably electrically and/or by the heat of combustion of H2, carbon monoxide and/or hydrocarbon as fuel. The hot conductor preferably is a pipe, in which residual gas can be burnt. The membrane preferably is electrically conductive or has a conductive coating. It is concentric and coaxial around the reaction zone and forms the wall of the reactor; and is permeable only for H2.Preferred Process: The steam reforming reaction and separation of H2 are carried out in a membrane reactor. The membrane is heated to 500-1000 degrees C and the reaction stream is introduced into the reactor and reacted on the membrane, preferably provided with catalyst, at 500-1000 degrees C. The H2 stream is discharged through the diffusion membrane. The H2 is stored in a tank, especially when the reformer is started, and preferably returned when the reactor/fuel cell is restarted or at output peaks. The residual gas stream is discharged through the reactor and burnt, preferably after removing carbon dioxide in the retentate, especially by liquefaction.Preferred Pretreatment Stage: The process water needed for steam reforming is vaporized in the pretreatment stage, in which the heat of hydrogenation preferably is high enough to heat the steam to the temperature required at the inlet to the membrane reactor. This preferably is carried out by passing the water through pipes heated to 400-600 degrees C, which are inside the pretreatment reactor. In this stage, aromatics in the fuel are hydrogenated and the fuel is gasified. H2 is used in large enough excess for satisfactory saturation of aromatics and cracking products.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The catalyst is a H2-permeable membrane containing a palladium/silver alloy.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Product: The n-paraffins produced in the pretreatment stream are mainly methane, ethane, propane and butane.