Synthesis of CO₂ adsorbent and research on adsorption isotherm model

The isotherm model can predict the performance of the carbon capture system. However, in the current research on the adsorption isotherm model, there is a problem of poor fitting results within specific temperature and pressure ranges, which affects the reliability of the prediction results. By preparing physical adsorbents 13X, amine-modified adsorbents PEI-NS, PEI-Al₂O₃, and TRI-Al₂O₃, and fitting the measured isotherms with four isotherm models of Langmuir, Freundlich, Sips, and Toth, the applicable isotherm models of each adsorbent at different temperatures were analyzed and obtained. Adsorption at 25 ℃, the fitting of 13X using the Sips model is better, and the fitting of amine-modified adsorbents using the Sips or Toth model is better. For the amine-modified adsorbents PEI-NS and TRI-Al₂O₃, they are greatly affected by the physical adsorption effect of CO₂, and the fitting result using the single isotherm model is poor. To address this problem, a segmented fitting method is proposed, and the R² in the low-pressure range is higher than 0.99. The working conditions sufficient for air carbon capture (the pressure of CO₂ in the atmosphere is approximately 0.4 mbar), proving that this method is helpful to significantly improve the accuracy of the isotherm model fitting results.