Preparation And Study Of Hydrophobic Carbon-based Coatings For CO₂ Adsorption

Carbon dioxide capture and storage from emission sources such as flue gas and natural gas has been recognized as an effective way to mitigate carbon emissions.Activated carbon has good thermal and chemical stability,low raw material cost,fast adsorption-desorption rate,and low energy consumption,so it has wide application in the field of CO₂capture.However,the density of powdered activated carbon is often small,and it is easy to cause dust pollution.In industrial application,honeycomb activated carbon is usually used,but the heat transfer efficiency of honeycomb carbon is relatively low.Moreover,the commonly used binder leads to a strong hydrophilicity of the material,which greatly affects the adsorption-desorption rate and adsorption capacity of the adsorbent in the practical aqueous flue gas.Therefore,this study focuses on the molding of powdered activated carbon and the hydrophobic modification of the adsorbent surface.The research contents mainly include:（1）The specific surface area of coconut shell activated carbon was found to be larger（1391.11 m²/g）,and it had higher CO₂adsorption capacity（25.7mg/g）and faster adsorption kinetics.When the mass ratio of CNF suspension to activated carbon was 2:1,the adhesion effect of the carbon-based coating was better.While when the mass ratio was 1.5:1,the maximum CO₂adsorption capacity of the adsorption coating was 38.8 mg/g at 40°C,which was 51%higher than that of the original activated carbon.（2）To improve the adsorption efficiency of the adsorbent in actual aqueous flue gas,a hydrophobic carbon-based adsorption coating（SAC-6-1.0）was prepared using a methyltrimethoxysilane（MTMS）modified binder.The adsorption capacity of SAC-6-1.0 for CO₂in dry flue gas（15 vol%CO₂）and wet flue gas（15 vol%CO₂+4.7 vol%H₂O）at 40°C and 1.0 bar was 39.4mg/g and 34.3 mg/g,respectively,and the adsorption capacity only decreased by 2.8%after 10 cycles.The SAC-6-1.0 also had fast adsorption and desorption kinetics and low heat of adsorption（26.10～28.50 k J/mol）.In addition,the metal heat exchanger tube improves the heating efficiency of the gas separation system,making the adsorbent heated uniformly during the warming and desorption process and simultaneously ensuring the stability of the adsorption-desorption process.（3）To further enhance the adsorption and separation of CO₂in wet flue gas,the nitrogen-oxygen co-doped carbon-based adsorbent（NAC-6-0.50）was obtained by adding an appropriate amount of N’N-methylenebisacrylamide（MBA）on the basis of hydrophobic modification of MTMS.The adsorption capacity of NAC-6-0.50 for CO₂in dry flue gas（15 vol%CO₂）and wet flue gas（15 vol%CO₂+4.7 vol%H₂O）were 48.9 mg/g and 42.3 mg/g,respectively,and the adsorption capacity decreased by 5.73%after 10 cycles.In this paper,coconut shell activated carbon and CNF were selected to prepare a carbon-based CO₂adsorption coating that can be applied to the outer surface of metal heat exchanger tubes to improve the adsorption-desorption rate by shortening the temperature change time of adsorbent;MTMS was used to hydrophobically modify the adsorbent to achieve efficient and stable separation of CO₂/H₂O in actual aqueous flue gas;MBA was introduced in the adsorbent preparation process to prepare nitrogen and oxygen co-doped carbon-based adsorbent to further improve the adsorption capacity of the adsorbent for CO₂in the wet flue gas.The results of this paper provide technical support for industrial CO₂capture.