Preparation Of VOCs Adsorption Materials Based On Carbon And Their Adsorption /desorption Properties Under Humid Air Condition

Volatile organic compounds（VOCs）are series of organic compounds that participate in atmospheric photochemical reaction,and are key precursors of PM_2.5 and O₃.In China,VOCs purification is crucial to air pollution control.Adsorption is the most widely used process of VOCs purification because of its high efficiency and technology reliability.Activated carbon is the most widely used adsorbent as it is cheap and easy to get.However,the existence of water would affect the adsorption of VOCs,and depress the adsorption efficiency.In order to prepare adsorption materials with excellent adsorption performance under high humidity conditions,activated carbons（ACs）were modified by liquid phase impregnation（L）,vapor deposition（g）,and liquid phase impregnation coupled with heat posttreatment（H）.Silanes,acyl chloride and ionic liquid were used for hydrophobic modification.The adsorption performances of toluene under humid air condition of activated carbons before and after modification were studied.Then the adsorption kinetics was further investigated to explore adsorption mechanism.Finally,the modified activated carbons saturated with toluene were regenerated by thermal method and Fenton method,respectively.The main contents and results are as follows:（1）Activated carbons（ACs）were modified by three methods of vapor deposition,liquid phase impregnation and liquid phase impregnation coupled with heat posttreatment with trimethylchlorosilane（TMCS）,polydimethylsilane（PDMS）,vinyltrimethoxysilane（VTOMS）,and phenyltriethoxysilane（PTES）,respectively.The sequence of toluene adsorption capacity was liquid phase impregnation coupled with heat posttreatment>vapor deposition>liquid phase impregnation under humid air condition with the identical modification reagent.Under the condition of 27℃and 77%relative humidity,the adsorption capacities of TMCS/PDMS/VTOMS/PTES-AC-H for toluene were about 166.29～196.73 mg/g,exceeding bare AC by 53%～82%.Simultaneously,the adsorption capacities of TMCS/PDMS/VTOMS/PTES-AC-H for water molecule were about 22.96～28.82 mg/g,accounting for 27%～35%of bare AC.All of the activated carbons before and after the silane modification were microporous materials.Different methods of hydrophobic silane modification could effectively enhance the contact angle of AC.Dynamic adsorption results showed that the breakthrough curves of AC before and after silane modification were consistent with Y-N model.These findings suggested that physical adsorption and chemical adsorption both played important roles in the adsorption of silane modified AC to toluene.（2）SC-AC（g）,SC-AC（L）,SC-AC-H were prepared by three methods of vapor deposition,liquid phase impregnation and liquid phase impregnation coupled with heat posttreatment with stearyl chloride（SC）,respectively.The sequence of toluene adsorption capacity was SC-AC-H>SC-AC（g）>AC>SC-AC（L）at 27℃and 77%relative humidity.The adsorption capacity of toluene on SC-AC-H was the highest（182.10 mg/g）,which was1.68 times that of unmodified AC,and the adsorption capacity of water molecule was the lowest（21.36 mg/g）,which was only 25.79%that of unmodified AC.All of the activated carbons before and after the stearyl chloride modification were microporous materials.Different methods of hydrophobic stearyl chloride modification could effectively enhance the contact angle of AC,and the contact angle of SC-AC-H was the biggest.Dynamic adsorption results showed that the breakthrough curves of AC before and after stearyl chloride modification were consistent with Y-N model.These findings suggested that physical adsorption and chemical adsorption both played important roles in the adsorption of stearyl chloride modified AC to toluene.（3）BMIMPF₆-AC（g）,BMIMPF₆-AC（L）and BMIMPF₆-AC-H were prepared by three methods of vapor deposition,liquid phase impregnation and liquid phase impregnation coupled with heat posttreatment with 1-butyl-3-methylimidazolium hexafluorophosphate（BMIMPF₆）,respectively.The sequence of toluene adsorption capacity was BMIMPF₆-AC-H>BMIMPF₆-AC（g）>AC>BMIMPF₆-AC（L）at 27℃and 77%relative humidity.The adsorption capacity of toluene on BMIMPF₆-AC-H was the highest（166.71 mg/g）,which was about 53.49%higher than bare AC,and the adsorption capacity of water molecule was the lowest（30.90 mg/g）,which was only 37.31%of that of bare AC.All of the activated carbons before and after the 1-butyl-3-methylimidazolium hexafluorophosphate modification were microporous materials.Different methods of hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate modification could effectively enhance the contact angle of AC.Dynamic adsorption results showed that the breakthrough curves of AC before and after 1-butyl-3-methylimidazolium hexafluorophosphate modification were consistent with Y-N model.These findings suggested that physical adsorption and chemical adsorption both played important roles in the adsorption of 1-butyl-3-methylimidazolium hexafluorophosphate modified AC to toluene.It can be concluded that the modification method of liquid phase impregnation coupled with heat posttreatment with trimethylchlorosilane,phenyltriethoxysilane,stearyl chloride and other hydrophobic reagents on activated carbons is effective to improve the adsorption capacity of toluene under humid air condition.（4）Thermal regeneration and Fenton regeneration were used to desorb the toluene saturated adsorbent of TMCS-AC-H,respectively.The results showed that the regeneration rate was the highest of 56.75%under the suitable Fenton regeneration conditions of436.76mmol·L^-1 H₂O₂,n（H₂O₂）/n(Fe²⁺)of 40,p H of 3 and temperature of 60℃.The thermal regeneration rate of TMCS-AC-H was 83.69%at 300℃.It can be concluded that although the regeneration efficiency of thermal regeneration is better than that of Fenton regeneration,Fenton reagent is also confirmed to be a feasible method to regenerate activated carbon under mild conditions.