The Research Of CO₂Adsorption By Modified Porous Materials

CO2is an important greenhouse gas, and an industrial resource as well. CO2in atmosphere, discharged from industry, can accelerate the process of greenhouse effect and also cause resource waste. Hence, it is of great economic and environmental significance to capture CO2effectively and economically from both the perspectives of environmental protection and resource conservation. Aimed at gathering CO2with low concentration at atmospheric pressure, porous carbon and silica materials with different chemical properties modified with amine compounds were synthesized and CO2adsorption behaviors on these adsorbents using fixed adsorption bed were investigated in this thesis. The influences of CO2initial concentration (2%-10%), adsorption temperature, the height of bed, gas flow rate and adsorbent morphology on adsorption were included in addition to the desorption performance of the tested adsorbents after adsorption at desorption temperature of80℃. The aim is to explore an efficient adsorbent for low-concentration CO2at atmospheric pressure to capture and recover CO2. The main conclusions are as follows:Among commercial activated carbon and two synthesized porous carbon with and without nitrogen, nitrogen-containing porous carbon has the highest adsorption amount of CO2with initial concentrations ranging from2%to10%at20℃. The adsorption variance between the two synthesized carbons is increased with high concentration. The effect of carbonization temperature at which the two carbons were prepared on adsorption is related to the existence of nitrogen in these adsorbents. When adsorption temperature is20℃,45℃or65℃, low adsorption amount is obtained with high temperature. After4times circulated desorption,91%of the adsorption capacity is kept for nitrogen-containing porous carbon, higher than the other porous carbon (86%) and activated carbon (85%).As for zeolite Y, the adsorption amount of CO2with initial concentration of10%on zeolite Y after amine polymerization in its pores are2.6times as much as the one before modification, indicating that adsorption of CO2on zeolite Y at atmospheric pressure and room temperature could be enhanced distinctly via amine polymerization. However, there is no positive correlation between the increased adsorption amount for modified materials and the polymerized amount of amine. Only68%of the intrinsic adsorption amount is achieved after4times circulated desorption. Yet,94%of the intrinsic adsorption amount could be retained if aqueous ammonia is added to desorb CO2before thermal regeneration.The as-synthesized mesoporous silicas HMS without calcination, with alcohol extraction or calcination were functionalized combined with tetraethylenepentamine and diethanolamine. All the three materials show higher adsorption amount of CO2with concentration of10%at20℃after functionalization than those primary ones. HMS with alcohol extraction shows the best enhanced adsorption via modification while the one with calcination the worst. HMS with calcination after modification even has a lower adsorption amount than HMS without calcination before modification. The adsorption amounts of CO2on the three adsorbents after functionalization are high with increased initial concentration, but the increasing trend of the one with calcination is less evident than the other two. When the temperature is20,45,65or75℃, all the three adsorbents after modification have the highest adsorption amount at65℃with the amount of CO2on HMS without calcination after modification reaching4.4mmol/g. After4times circulated desorption,97.5%of the intrinsic adsorption amount could be achieved for HMS without calcination after modification, higher the other two adsorbents after modification.Additionally, the morphology of nitrogen-containing porous carbon in adsorption bed has an effect on CO2adsorption. The carbon with netlike shows the best adsorption performance followed by sheet carbon and powder carbon in sequence. There is a peak of gas flow rate within the tested range. With the bed height of1cm,2cm,3cm or4cm, CO2adsorption amount is increased as the bed heightens. After4times circulated desorption,91%of the intrinsic adsorption amount could be achieved for netlike nitrogen-containing porous carbon.