Carbon dioxide adsorption properties and adsorption/desorption kinetics of amine-functionalized KIT-6

An amine-functionalized adsorbent was prepared by loading pentaethylenehexamine (PEHA) into the pores of KIT-6 mesoporous silica. Nitrogen adsorption/desorption, thermogravimetric analysis, and X-ray powder diffraction were employed to analyze the structural properties of the prepared adsorbents. The results reveal that the pore size, pore volume, and surface area of the adsorbents decrease after PEHA loading in KIT-6, while the basic KIT-6 pore structure remains unchanged. The CO2 adsorption performance of amine-functionalized KIT-6 was studied by isothermal CO2 adsorption, adsorption/desorption cycle regeneration testing, and multiple cycle tests. The amount of CO2 absorbed increased with increasing temperature in the temperature range of 303-343 K, achieving a maximum adsorption capacity of 3.2 mmol/g-adsorbent at 343 K. For temperatures greater than 343 K, the adsorption capacity decreased with increasing temperature. The amount of CO2 adsorbed remained nearly constant after 10 adsorption/desorption cycles. The CO2 adsorption/desorption kinetics of the PEHA-impregnated KIT-6 were investigated using three kinetics models. The results indicate that the CO2 adsorption process by the amine-functionalized adsorbent is dominated by intra-particle diffusion, and the adsorption rate is restricted by the intra-particle diffusion process. In addition, high CO2 partial pressure facilitates the adsorption of CO2. The CO2 adsorption breakthrough curves obtained by the deactivation model were in good agreement with the results of this study. The adsorbents were regenerated by vacuum and temperature swing adsorption regeneration. The results indicate that increasing the desorption temperature is an effective means of reducing the regeneration time. The absolute value of the activation energy obtained from the Arrhenius equation for CO2 desorption was 81.992 kJ.mol(-1), which was greater than that obtained for adsorption.