Applying molecular dynamics simulation and computer graphics methods we have investigated the dynamic behavior of the separation process of CO2 from the CO2/N-2 gas mixture inorganic membranes at high temperatures. We have demonstrated that the permeation dynamics follows the Knudsen diffusion mechanism in our model system that has a slit-like pore of 6.3 Angstrom. We have analyzed the effect of affinities of gas molecules for the membrane wall on the permeation to predict the optimal affinity strength for high selectivity of CO2. Our results indicate that in the model with the 600 K and 200 K affinities for CO2 and N-2, respectively, we can obtain a high selectivity of CO2 even if the temperature is 1073 K. It is also shown that there is an optimal range for the CO2 affinity for the membrane wall to achieve good separation, which was estimated as the range of 400-600 K in our system, if the affinity of N-2 is always weaker than that of CO2.