Gas permeation in hollow fiber membranes with nonlinear sorption isotherm and concentration dependent diffusion coefficient

Gas permeation in membranes of cylindrical geometry (hollow fiber) is studied. Mathematical formulation is derived for the time-lag method, assuming Langmuir sorption equilibrium and Darken-type diffusion. Analytical expressions for the steady state concentration profile and the rate of permeation are also provided. It is demonstrated that the use of the traditional time-lag expression for a slab image in the place of a hollow fiber may incur large errors for both adsorbing and weakly adsorbing gases.