Nitrogen is to be removed from a gas mixture with methane by gas permeation (see Table 1.2)

Question:

Nitrogen is to be removed from a gas mixture with methane by gas permeation (see Table 1.2) using a glassy polymer membrane that is selective for nitrogen. However, the desired degree of separation cannot be achieved in one stage. Draw sketches of two different two-stage membrane cascades that might be considered to perform the desiredseparation.