Research On The Adsorption Performance Of VOCs On Y Zeolites

Y zeolite is an ideal adsorbent for its high hydrothermal stability, large surface area and moderate pore size characteristics. It is considered as a good alternative for activated carbon that is flammable, easy to get the pore block and difficult to regenerate. Accordingly, Commercial NaY zeolite was chosen to be the study object for this disseration, and the following three issues were studied:(1)The superior nature of low-silica NaY to other zeolites (2)Methods to raise the Si/Al ratio and hydrophobicity properties of NaY zeolite, (3) The adsorption behavior of high silica Y zeolite.Firstly, the superior adsorption/desorption performance of low-silica NaY zeolites than other five zeolites (ZSM-5, 13X, Hβ, MCM-22. MCM-41) were studied. The adsorption thermodynamics study showed that low-silica NaY possessed the lagerest adsorptive enthalpy values among all the zeolites, which meant the adsorption intensity between NaY and organic molecules was the strongest. The adsorptive properties of zeolites were investigated by method of breakthrough curves. The results showed that NaY zeolites has a high adsorption capacity for different VOCs, and its adsoption performance is similar with that of activated carbon. However the hydrophobicity of NaY zeolite is so poor that it could hardly adsorb toluene molecules in the 50% relative humidity environment.In order to improve the hydrophobicity of NaY zeolite, high temperature hydrothermal dealumination technique was used to prepare ultra-stable high-silica HY zeolite. The influences of modification conditions such as water vapor flows and NH₄⁺ exchange degree on the crystal structure and adsorption ability of HY were studied. The results showed that the Si/Al ratio of HY zeolite increased with the increase of water vapor flows and NH₄⁺ content. But specific surface area of HY would decrease with Si/Al ratio. The high-silica HY zeolite (Si/Al=22.55) shows an excellent hydrophobicity while its adsorption capacity is seriously decreased.To further maintain the high surface area of high-silica Y zeolite, La³⁺ ions was introducted to reinforce framework of Y zeolite. The results showed that La³⁺ introduction improved the hydrothermal stability of HY zeolite. When the Si/Al ratio of LaY zeolite reached 23.91, its surface area could still maintain 589.71m²/g. Besides, non-framework aluminum in the secondary hole of LaY could be digged out by the dilute HCl treatment, which increased the surface area and adsorption properties of LaY. Toluene adsorption experiments showed that high-silicon LaY zeolite had a strong hydrophobicity. Under 50% humidity environment, its toluene adsorption capacity could still reach to 0.136g/g.The adsorption property of high-silica Y zeolite is studied through the competitive adsorption behavior between water vapor and VOCs. The results indicated that with the increase of Si-Al ratio, Organic molecules adsorbed in zeolite Y were more competitive than water molecules, and adsorption properties of different VOCs were associated with their molecular polarity.