Polyethyleneimine-nano silica composites: a low-cost and promising adsorbent for CO2 capture

Adsorbents for CO₂ captured with nano silica as support were synthesized by impregnating polyethyleneimine (PEI) into nano silica. For impregnation of PEI into nano silica, the 2–40 nm pore of silica support plays an important role in the synthesis process of adsorbents. The PEI loading content, adsorption temperature and CO₂ partial pressure influenced CO₂ adsorption capacity and PEI utilization efficiency. At 105 °C and under 1 atm CO₂ partial pressure, the adsorbent with 60% PEI loading content obtained a CO₂ adsorption capacity of 186 mg g⁻¹ adsorbent and a PEI utilization efficiency of 304 mg g⁻¹ PEI. The CO₂ cycling adsorption–desorption was tested under the condition as follows: adsorption at 90 or 105 °C under pure CO₂ and desorption at 120 °C under pure N₂ showed relatively good adsorption–desorption stability, and no evident deactivation of amines was observed under this condition. However, for adsorption at 90 or 105 °C under pure CO₂ and desorption at 135 or 150 °C under pure CO₂, evident deactivation of amines occurred, and the formation of linear or cyclic urea is one reason which led to the decrease of CO₂ adsorption capacity.