In this study, the CO2 gas absorption process has been investigated modeling in order to find suitable adsorbent, as well as determination of the solubility and mass transfer mechanism. To calculate the solubility of CO2 in a solution of triethanolamine and piperazine, the CPA state equation will be used to predict the properties of the system. The results show that with increasing pressure, the absorption of Co2 in the gas phase increases due to the increase of the CO2 absorption of density gradient. By increasing the temperature, the amount of CO2 absorbed in the adsorbent solution decreases, due to the calorific of the Co2 absorption by the use of an amine absorbent solution. Also, by increasing the concentration of piperazine in the amine absorbent solution, the amount of CO2 absorption increases as a result of increasing the reaction rate of the amine solution with CO2 in the presence of piperazine. The highest overall error rate obtained from the reported data for operating pressure, temperature and piperazine concentrations variable is 7.3%, 7.4% and 4%, which is considered an acceptable error rate, respectively.