The properties of calcium-modified ETS-4 are studied focusing on olefin–paraffin separation by PSA (Pressure Swing Adsorption), specifically a stream containing CH4/C2H6/C2H4. The effect of activation temperature of Ca-ETS-4 is studied to perform a kinetic separation, with the aim of excluding paraffin molecules from the pores. Adsorption isotherms of pure CH4, C2H6, and C2H4 were measured at 303 K after activating the sample at different temperatures (from 463–583 K). Furthermore, pulse chromatography of single gases at 303 K was carried out after different activation temperatures to determine the heating effect on diffusion of pure gases. Aiming to develop a faster procedure to determine optimal activation temperature for alkali-exchanged ETS-4, a correlation between changes in the crystal lattice parameters from in situ XRD and the diffusion constant has been established for Ca-ETS-4.