Mixed Alkanolamine-Polyethylenimine Functionalized Silica for CO2 capture

High amine efficiency amine-modified silica adsorbents with fast adsorption rates have been developed by adding amine species including hydroxyl groups into polyethyleneimine (PEI)-loaded mesoporous silica for CO2 capture. Two amine species of diethanolamine (DEA) and 3-amino-1,2-propanediol (AP) including hydroxyl groups were introduced into PEI to reduce the CO2 diffusion resistance and increase the active CO2 adsorption sites. The DEA promoted adsorbents were found to exhibit much higher adsorption capacity than AP promoted adsorbents. Through tuning the ratio of PEI to DEA in amine mixture during adsorbent impregnation step, a threshold value of PEI/DEA weight ratio (similar to 50 : 50) was found, where the maximum CO2 capacity of 2.93 mmol/g was achieved under dry CO2 at 35 degrees C.The adsorption capacity for this newly synthesized adsorbent increased by 50 % in comparison to PEI-silica materials. Their amine efficiency was 0.40 mol CO2/mol N, which was more than twice than that of PEI-silica (0.17 mol CO2/mol N). Under simulated humid flue gas conditions, the DEA promoted adsorbents had a CO2 breakthrough capacity q(b) of 1.57 mmol/g and a CO2 capacity q(50) of 2.49 mmol/g. Such adsorbents possess good reversibility and the adsorption capacity is nearly stable after two adsorption-desorption cycles. The synthesis methodology reported in this investigation proves to be an efficient strategy to develop highly efficient amine-impregnated adsorbents.