Effect of Pore Structure of Alkali Modified ZSM-5 Zeolite on Its VOCs Adsorption Performance
A series of modified ZSM-5 zeolites were prepared via sodium hydroxide and tetrapropylammonium hydroxide mixed alkali solution.The modified samples were characterized by means of X-ray diffraction(XRD),scanning electron microscopy(SEM),N2adsorption and water contact angle determination.Meanwhile,the dynamic adsorption performance of 5A,NaY,and different alkali-modified ZSM-5 zeolite adsorbents for n-hexane and ethyl acetate were comparatively evaluated on a customed fixed-bed adsorber.The results show that the alkali-modified ZSM-5-G-3 zeolite sample with the molar concentration of sodium hydroxide and tetrapropylammonium hydroxide of 0.2 mol/L have the specific surface area and pore volume of 425 m2/g and 0.585 cm3/g respectively,17.7％and 174.6％higher as compared with the parent samples of high-silicon ZSM-5-G-1 zeolite.In addition,the specific surface area and pore volume for ZSM-5-G-3 are observed as being 317 m2/g and 0.531 cm3/g,which are 9.6 and 13.3 times higher than those of ZSM-5-G-1,respectively.With an increase in the concentration of alkali solution,the water contacting angle of the modified zeolite decreases.At 25 ℃,n-hexane and ethyl acetate exhibit the breakthrough adsorption capacities of 76.99 mg/g and 101.08 mg/g in the fixed-bed adsorber filled with ZSM-5-G-3,indicating an increase of 40.3％and 17.4％compared to the parent adsorbent of ZSM-5-G-1.Furthermore,the significantly improved adsorption performance of the modified ZSM-5-G-3 zeolite for volatile organic compounds(VOCs)is mainly attributed to more adsorption sites and mesopore structures provided by alkali modification.
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