Study Of CO₂ Adsorption Performance Of Tannic Acid-based Porous Carbon

Activated carbons are important adsorbents for carbon capture,which show great potential for application.In this thesis,we characterized the prepared tannic acid-based activated carbon and investigated the relationship between its pore size structure and surface chemistry and CO₂ adsorption performance.Then,we investigated the mechanism of different activation conditions on the activation reaction,explored a more suitable process method for the preparation of CO₂ adsorption activated carbon products,and examined the CO₂/N₂selectivity and cycling stability of activated carb on.The main contents and research results are summarized as follows.1.The effects of activators on the microporous structure and CO₂ adsorption performance of activated carbon were clarified.Activated carbons with well-developed microporous structures were prepared from tannic acid with K₂CO₃ and KOH as activators,respectively.They were characterized using N₂ adsorption/desorption isotherms,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray diffraction（XRD）.The results showed that the tannic acid-based porous carbon prepared by KOH activation had better adsorption capacity for CO₂ than the K₂CO₃-activated activated carbon material,and the use of doping with N atoms could not improve the adsorption capacity of this material for CO₂.2.The effects of KOH-to-carbon ratio and activation temperature on the microporous structure and CO₂ adsorption performance of activated carbon were clarified.High-performance tannic acid-based porous carbon was prepared with KOH as the activator and tannic acid as the raw material,and the effects on the adsorption performance and cyclic adsorption and desorption performance of CO₂ were investigated.The results showed that the tannic acid-based activated carbon had the best adsorption capacity of CO₂ when the pretreatment-chemical activation method was used,the activation temperature was 600 ^oC,the carbon to base ratio was 2,and the activation time was 2 h.The adsorption capacity of CO₂reached 7.03 mmol/g at 0 ^oC and 1 bar,which was significantly higher than most of the reported biomass-based activated carbons,it not only has good adsorption selectivity for CO₂in the presence of N₂,but also has excellent cycling stability.3.The relationship between the microporous structure of activated carbon and CO₂adsorption performance was clarified.The pore structure of activated carbon was characterized by N₂ adsorption/desorption isotherms,and the surface chemistry of activated carbon was characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray diffraction（XRD）.The results showed that the pore capacity of the micropores was the key factor to determine the performance of CO₂ adsorption on activated carbon,in which the micropores of 0.33-0.86 nm had a greater influence on the CO₂adsorption capacity at 1 bar and 0 ^oC.As the adsorption temperature gradually increased from0 ^oC to 25 ^oC,the pore size range of narrow micropores,which played a major role in CO₂adsorption,decreased from 0.33-0.86 nm to the pore size range of narrow micropores,which are the main contributors to CO₂ adsorption,decreased from 0.33-0.86 nm to 0.33-0.70 nm.4.The fitting of kinetic equations for CO₂ adsoption experiment date of tannic acid-based porous carbon samples was investigated.The results show that the Freundlich model indicates that the adsorption of CO₂ consists of physical and chemical adsorption,with physical adsorption dominating and chemical adsorption occurring on the oxygen-containing functional groups of the samples.The experimental data of adsorption showed good agreement with isothermal models（Langmuir,Freundlich,Redlich-Peterson,Toth,and Sips）with high R² values（0.99）and small standard deviationsΔq（≤10%）.At the same time,the three-parameter model was fitted with better accuracy than the two-parameter model.