Hydrogen (H₂) is selectively separated from nitrogen (N₂) by permeation through a polymeric hollow fiber membrane. The driving force is the partial pressure difference across the membrane for H₂, N₂ and other gas components. H₂ is the “fast” gas, whereas methane (CH₄) and N₂ are “slow” gases. The pressurized feed gas enters the bundle from the shell side; the nitrogen, methane and argon stay under pressure while the H₂ is collected at a lower pressure from the fiber bore.