TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process Details: The hydrocarbon effluent is a cut of dry gas from a process which may be fluidized bed catalytic cracking (preferred), vapor reforming, catalytic reforming, gasification, partial oxidation, an autothermic process associating reforming and partial oxidation, cokefaction or viscoreduction. The catalyst is used in the form of balls or extrudates and comprises a group VIII metal on an organic or inorganic support. The support is chosen from group II, III or IV oxides, alone or mixed with other oxides, carbon, zeolites or mixtures of metals with a zeolite. The active phase of the catalyst, nickel (Ni), platinum (Pt) or Ni/Pt, is partly integrated with the membrane. The operating conditions for stages (a) and (b) are a supply pressure of 0.2-5 MPa and a pressure downstream of the membrane of 0.1-0.5 MPa. The VVH of the flow containing the unsaturated compound(s), in stage (b), is 0.5 - 30 hour-1 relative to the hydrogenation catalyst. The permeation membrane may be based on carbon fibers or microporous silica on a porous support, zeolites supported by porous or metallic matrices, mixed oxides or an alloy of palladium (Pd) with another metal. An inorganic membrane can be used at 20-280degreesC. The membrane may also be organic, chosen from polyimides, polyaramides, polycarbonates, polysulfones and polyvinyl fluorides. Their operating temperature range is 20-180degreesC. The charge to be treated, containing hydrogen sulfide (H2S) and/or carbon monoxide (CO), is pre-treated to remove them by selective capture or preferential adsorption, using a membrane permeable to H2S and/or CO. The process also includes a stage (d) of dehydrogenation of the hydrogenated compound(s) from (c) to recover part of the H2 consumed by hydrogenation. Preferably, the flow on the downstream side of the membrane contains one or more aromatic hydrocarbons, hence stage (d) is a reforming reaction. More preferably, the flow is a naphtha cut obtained from atmospheric distillation. EXAMPLE - A charge to be separated comprised a typical dry gas from a fluidized bed catalytic cracking unit, and contained 27% (molar) of H2. Tubular metallic membranes comprising a palladium/silver (Pd/Ag) alloy (23% Ag) were used in the separation, at 250degreesC. and 1.5 MPa. The pressure downstream of the membrane was 0.2 MPa. The membranes were permeable only to H2 and gave total selectivity of separation of H2 from hydrocarbons and CO. The reforming charge was composed of 63.55% paraffins, 22.95% naphthenes and 13.47% aromatics. This was hydrogenated on a Ni catalyst by the permeate. The catalyst contained 20% Ni as oxide on a transition alumina of 130 m2/g surface area, which had previously been activated by contact with H2 at 400degreesC. The molar composition of the reaction mixture was 18% permeate and 82% reforming charge. Conversion of H2 was 99% at a VVH of 10 hour-1 and a 50% recovery of H2 was obtained. The hydrogenated naphtha was then directed to a catalytic reforming process to recover the H2.