Thermodynamic study on amine-modified adsorbent of CO₂ adsorption at low CO₂ partial pressures

To reduce the greenhouse effect, effective measures should be taken to reduce the emissions of CO₂. Amine-modified adsorbents are considered as important adsorbent materials to capture CO₂. In this paper, a balance model was established to describe the adsorption isotherms of amine modified MCM-41 under low CO₂ partial pressure and the thermodynamic parameters was calculated. The model was based on Dual-site Langmuir model and assumed that there were two independent adsorption mechanisms: chemical adsorption on amine groups and physical adsorption via surface area. In order to distinguish the physical adsorption and chemical adsorption of amine modified adsorbents, a new method based on adsorption of non-modified adsorbents and surface area was proposed. The results showed that the model could fit well with the measured adsorption isotherms. The calculated physical and chemical adsorption heats are -25.4 kJ/mol and -41.9 kJ/mol respectively, the total adsorption heats is -67.3 kJ/mol, which were in accordance with the experimental data. The saturation adsorption capacity of MCM-41-TEPA could reach 7.79 mmol/g.