The permeability of carbon dioxide and methane are and , respectively. Thus, the selectivity, .

The high (retentate side) and low (permeate side) pressures are 20.0 and 1.1 atm, respectively.

The Demonstration plots (1) the RT curve, which relates mole fractions on both sides of the membrane, and (2) the operating line, whose slope depends on the stage cut, .

Assuming that both retentate and permeate sides are well mixed, the graphical solution of this gas permeation problem is given by the intersection point shown in cyan in the figure. You can set the value of the feed composition (i.e. mole fraction of ) as well as the stage cut.