An apparatus for producing a H 2 -containing product stream and CO-containing product stream from a process gas, the apparatus comprising: (a) a synthesis gas production unit for generating the process gas, the process gas comprising H 2, CO, CO 2, and H 2 O; (b) a water removal unit for removing H 2 O from the process gas; (c) a CO 2 removal unit for removing CO 2 from the process gas without cryogenically fractionating the process gas; (d) a pressure swing adsorber for separating H 2 from the process gas thereby forming the H 2 -containing product stream and a residual gas stream; (e) a compressor for compressing the residual gas stream; (f) a cryogenic separation unit for receiving the residual gas stream after the compressor and after the mixing device, the cryogenic separation unit for separating the residual gas stream into the CO-containing product stream, a H 2 -enriched stream, a methane-enriched stream, and a CO-containing intermediate stream by cryogenic fractionation in the cryogenic separation unit; and (g) a conduit for recycling at least a portion of the H 2 -enriched stream to the pressure swing adsorber; characterized in that the apparatus further comprises: (h) a mixing device for attenuating the amplitude of the molar concentration of one or more components in the residual gas stream to less than 1 mole %, wherein the amplitude of the molar concentration of a component is the difference between an extreme of the molar concentration of that component during a cycle of the pressure swing adsorber and the time-averaged mean molar concentration, C, of that component wherein C ̅ = 1 T ∫ 0 T C t ⋅ dt, where C(t) is the molar concentration of the one or more components as a function of time, t is the time variable, and T is the time for the pressure swing adsorber to complete one cycle; and (i) a second mixing device operatively connected between the compressor and the cryogenic separation unit for dampening pressure variation of the residual gas and further attenuating the amplitude of the molar concentration of one or more components in the residual gas before the residual gas is passed to the cryogenic separation unit. (a) a synthesis gas production unit for generating the process gas, the process gas comprising H 2, CO, CO 2, and H 2 O; (b) a water removal unit for removing H 2 O from the process gas; (c) a CO 2 removal unit for removing CO 2 from the process gas without cryogenically fractionating the process gas; (d) a pressure swing adsorber for separating H 2 from the process gas thereby forming the H 2 -containing product stream and a residual gas stream; (e) a compressor for compressing the residual gas stream; (f) a cryogenic separation unit for receiving the residual gas stream after the compressor and after the mixing device, the cryogenic separation unit for separating the residual gas stream into the CO-containing product stream, a H 2 -enriched stream, a methane-enriched stream, and a CO-containing intermediate stream by cryogenic fractionation in the cryogenic separation unit; and (g) a conduit for recycling at least a portion of the H 2 -enriched stream to the pressure swing adsorber; (h) a mixing device for attenuating the amplitude of the molar concentration of one or more components in the residual gas stream to less than 1 mole %, wherein the amplitude of the molar concentration of a component is the difference between an extreme of the molar concentration of that component during a cycle of the pressure swing adsorber and the time-averaged mean molar concentration, C, of that component wherein C ̅ = 1 T ∫ 0 T C t ⋅ dt, where C(t) is the molar concentration of the one or more components as a function of time, t is the time variable, and T is the time for the pressure swing adsorber to complete one cycle; and C(t) is the molar concentration of the one or more components as a function of time, t is the time variable, and T is the time for the pressure swing adsorber to complete one cycle; and (i) a second mixing device operatively connected between the compressor and the cryogenic separation unit for dampening pressure variation of the residual gas and further attenuating the amplitude of the molar concentration of one or more components in the residual gas before the residual gas is passed to the cryogenic separation unit.