Preparation Of Sulfur-doped Activated Carbon And Its Adsorption Properties

Activated carbon has a well-developed pore structure and superior adsorption capacity.As a result,it has been widely applied in many fields,such as gas purification,wastewater treatment,solvent recovery,heavy metal recovery,gas storage,electric double-layer capacitors and so on.The adsorption selectivity of activated carbon to carbon dioxide is remarkably improved by doping nitrogen,sulfur,phosphorus or boron into activated carbon framework.The doping methods mainly include in situ doping and post-treatment.The in situ doping method is the direct activation of heteroatom-containing raw materials,The process is very simple,and has good prospects for development.Sulfur-doped activated carbons?CSP,CSZ and CSK?were prepared with an in situ doping method.Phosphoric acid,zinc chloride and potassium hydroxide acted as activators,and poly?4-styrenesulfonate?acted as raw material in the preparation process.The suitable preparation conditions of CSP activated carbon were as follows:activation temperature was 800?,phosphoric acid concentration was 0.10 mol/L,activation time was 60 min.The highest specific surface area reached 884m²/g after phosphoric acid activation.The optimum preparation conditions of CSZ activated carbon were as follows:the concentration of zinc chloride was 1.00 mol/L,the activation time was 60 min and the activation temperature was 800?.After activated by zinc chloride,the specific surface area could reach 880 m²/g.The highest specific surface area of CSK activated carbon was about 2088 m²/g,which was much higher than that in CSP and CSZ.The suitable preparation conditions for CSK were as follows:the ratio of the mass of potassium hydroxide to raw carbon was 4:1,activation time was 180 min,activation temperature was 800?.Typical samples were selected to measure the pure gas isotherms at low adsorption pressure.The adsorption selectivity of the samples were estimated by the multi-component adsorption equilibrium data,calculated by the Ideal Adsorption Solution Model?IAST?.The results showed that doping sulfur could improve the CO₂/CH₄ separation selectivity.CS,which was the highest content of sulfur,had the highest separation selectivity.The higher content of sulfur in samples was,especially the sulfur content of non-oxidized state?C-S-C?,the better adsorption selectivity of activated carbon to CO₂ was.The CH₄/N₂ separation coefficients were varied from 2.0to 4.3,which were mainly affected by the pore structure of activated carbon.The activated carbons with the largest surface area and pore volume were selected from CSZ and CSK for high pressure adsorption experiment.The results showed that the Langmuir-Freundlich model was more accurate than Langmuir model to describe the adsorption behavior of sulfur-doped activated carbon on CO₂,CH₄ and N₂.The adsorption of CO₂,CH₄ and N₂ on sulfur-doped activated carbon was mainly physical adsorption,and both isosteric heat of adsorption and limit heat of adsorption decreased in the order:CO₂>CH₄>N₂.The methane sorption capacity of CSK5 loaded with water was 74%higher than that of dry CSK5.After adding hydrate promoter tetrahydrofuran?THF?into mesoporous carbon,the formation pressure of carbon dioxide hydrate was reduced from 1.75 MPa to about 0.25 MPa,which can be used for carbon dioxide capture and separation process.The suitable amount of THF promoter was 6.7 mol%in this work.