Polyethyleneimine-Modified Amorphous Silica for the Selective Adsorption of CO₂/N₂ at High Temperatures

Mechanochemistry is very attractive as an efficient, solvent-free, and simplified technique for the preparation of composite adsorbents. Here, a series of polyethyleneimine (PEI)-modified SiO₂ adsorbents were prepared via mechanical ball milling for selective adsorption of CO₂ at high temperatures. The structural properties of these adsorbents were characterized by XRD, SEM, TGA, FTIR, and N₂ adsorption–desorption. This method can better disperse the PEI evenly in the SiO₂ as well as maintain the porous structure of the adsorbents by comparing with the impregnated adsorbents. These adsorbents presented appreciable performance in separating CO₂ at high temperatures, and the CO₂ adsorption capacity of PEI(70%)/SiO₂ is up to 2.47 mmol/g at 70 °C and 1.5 bar, which is significantly higher than that of the same type of CO₂ adsorbent reported in the literature. Furthermore, the adsorbent of PEI(70%)/SiO₂ provided an ideally infinite selectivity for CO₂/N₂ (15:85) at 70 °C. These results showed that mechanical grinding methods are a simple and effective approach to producing amine-modified silica composite adsorbents.