To design separation processes based on adsorption, accurate and reliable equilibrium data is needed. In the preliminary studies, the separability of the desired mixture should be checked on the selected adsorbents. For this purpose, in the present study, the modeling of the two-component adsorption of the Carbon dioxide and Nitrogen system on Zeolite 13X and Zeolite 13X-active carbon composite adsorbent was done. In addition, through the Ideal adsorbed solution theory, the amount of absorbed carbon dioxide and nitrogen was estimated. Furthermore, the absorbed values, ideal selectivity, and spreading pressure in two different states of the constant pressure of 1bar and temperatures of about 310, 300, and290 K as well as the constant temperature of 300 K and pressures (0.5, 1, and 1.5) for Langmuir, Freundlich, Sips isotherms were predicted. The results showed that the theory of Ideal adsorbed solution has a good potential for predicting the adsorbed amount of Carbon dioxide. Also, the amount of Carbon dioxide adsorbed on the Zeolite 13Xactivated carbon composite adsorbent is more than that of Zeolite 13X. In addition, the adsorbed amount increases with increasing pressure, the mole fraction of Carbon dioxide, and decreasing temperature. Also, the results of the effect of selectivity for both adsorbents in temperature, pressure, and different mole fractions showed that with increasing pressure, temperature, and mole fraction, the selectivity (Carbon dioxide) decreases and vice versa. For this reason, to separate Carbon dioxide from Nitrogen, it is better to apply it at a lower temperature, pressure, and molar fraction. From a general point of view, it can be said that the selectivity value of the composite adsorbent for carbon dioxide shows a relatively better performance, which indicates the greater tendency of Carbon dioxide to be adsorbed on the composite adsorbent and also indicates the superiority of this adsorbent in separation systems. Carbon dioxide is from