NOVELTY - In purification of hydrogen gas (H2) from a gaseous mixture by (a) passing the mixture through a selective permeation membrane, giving H2-enriched permeate and H2-depleted retentate, (b) compressing the permeate and (c) purifying H2 in the permeate by pressure swing adsorption (PSA), one of the two regeneration streams leaving the adsorber(s) for step (c) is supplied to the compressor for stage (b), to be compressed before recycling to the adsorber(s).    USE - For purifying hydrogen (H2) contained in a gaseous mixture, specifically containing natural gas (claimed). In particular the process and apparatus are useful for recovering pure H2 (as 'clean' fuel) from H2 transported (as a mixture with natural gas) through an existing natural gas network, at a site of use of the H2, e.g. for supplying fixed fuel cells or for refuelling vehicles driven using fuel cells, hydrogen turbines or hydrogen-fuelled combustion engines.    ADVANTAGE - The need to use two or more compressors (as in US4690695) is eliminated, without reducing the effectiveness of the membrane filtration stage and without reducing the partial pressure difference between the H2 and the membrane. The compressor (4) is the specifically the sole compressor in the overall plant (claimed).    DETAILED DESCRIPTION - Purification of hydrogen gas (H2) from a gaseous mixture involves (a) enriching the H2 by passing the mixture under high pressure (P1) through a selective permeation membrane, giving H2-enriched permeate under a low pressure (P2) and H2-depleted retentate under pressure P1; (b) compressing the permeate to a high pressure (P3); and (c) purifying H2 in the permeate by pressure swing adsorption (PSA), using adsorber(s) subjected to a cycle of an adsorption phase under pressure P3 and a regeneration phase. The novel feature is that one of the two regeneration streams leaving the adsorbers in the adsorption phase is supplied (directly or indirectly) to the compressor for stage (b), to be compressed to the pressure P3 before recycling to the adsorber(s). An INDEPENDENT CLAIM is included for H2 purification apparatus, comprising a selective permeation membrane filtration module (2), supplied with a natural gas mixture containing H2; a PSA device (3) for purifying H2, downstream of the filtration module, generating a pure H2 stream and two regeneration streams; and a compressor (4), between the filtration module and PSA device, to compress both (i) the permeate from the filtration module and (ii) one (8) of the regeneration streams from the PSA device.    DESCRIPTION OF DRAWING(S) - The figures show schematic views of two forms of plants for purifying hydrogen in gaseous mixtures circulating in natural gas transport networks.    Natural gas transport network (1)    Membrane filtration module (2)    Pressure swing absorption device (3)    Compressor (4)    Gaseous mixture extraction line (5)    Retentate recycling line (6)    Permeate exit line (7)    Line for recycling regeneration stream to compressor (8)    Non-recycled regeneration stream line (9)    Natural gas distribution network (10)    Line for supplying part of regeneration stream to filtration module (11)