The present paper describes the first sequence of the Skarstrom cycle for bed 1 to analyze the breakthrough curves and study the importance of the mass transfer resistance for the performance of the PSA process which separates a feed stream consisting of equimolar fractions of methane and ethane. The beds are filled with carbon nanotubes (CNT) of a certain inner diameter (3 nm). The adsorption bed is simulated by a one-dimensional, time-dependent dispersion model. A special feature of the present paper are the adsorption isotherms of the CH4/C2H6 mixtures and the diffusivities which were calculated by molecular simulation methods.