Preparation And Adsorption Properties Of Magnetic Silicalite-1

Silicalite-1 is an important molecular sieve with MFI structure,and does not contain aluminum atoms. It has some properties such as lipophilicity and hydrophobicity due to lack of strong electrostatic adsorption center-cations, then it is usually used for absorbing organic isomers、recovering and concentrating ethanol from the fermentation broth,、or separating and recovering organics from waste water.When the Silicalite-1 powder is used as adsorbent, it needs to separate from liquid solution when the adsorption attained to saturate, Silicalite-1 can be reused after regeneration.As a result of the diameter of Silicalite-1 is very small, it is hard to separate from the liquid. In this work we proposed to synthetic magnetic Silicalite-1, it can be separated rapidly in magnetic condition, and solve the problem of solid-liquid separation.Magnetic Silicalite-1 was synthesized successfully through hydrothermal method by adding magnetic materials-NiFe₂O₄. The samples were characterized by X-ray diffraction（XRD）、fourier transform infrared spectroscope（FT-IR）、Nitrogen adsorption desorption、transmission electron microscope（TEM）、scanning electron microscope（SEM）、vibrating sample magnetometer（VSM）. The adsorption properties of Silicalite-1 and magnetic Silicalite-1 to ethanol aqueous solution was characterized by Gas Chromatography.In order to obtain the optimal conditions of synthesizing Silicalite-1, examined the effects of reaction molar ratio, crystallization temperature and crystallization time to the structure and properties of product. The results showed that the optimal conditions for synthesis of Silicalite-1 is: TEOS: TPAOH: H2 O = 1: 0.2: 80, the crystallization temperature is175 ℃, the crystallization time is 24 h, on this basis, magnetic Silicalite-1 is synthesized.XRD、FT-IR and Nitrogen adsorption desorption results show that the add of nickel ferrite particles（NiFe₂O₄） was not destroyed the structure of Silicalite-1, and it has little effect topore structure. The results showed that when the amount of NiFe₂O₄ was 30%, the magnetic Silicalite-1 particles have a high specific surface area, an even super paramagnetic, saturation magnetization is 1.4363 emu·g-1, cylinder、distribution uniformly, with an average size 300⁵00nm in diameter, the magnetic recovery rate can reach more than 93%.The Silicalite-1 and magnetic Silicalite-1 were applied to the aqueous ethanol, in room temperature the maximum amount of saturated adsorption of ethanol were 336.6 mg/g and246.8 mg/g respectively, but the magnetic Silicalite-1 can be separated quickly from the magnetic field. The adsorption model were consistent with the Langmuir model, and the adsorption kinetics were matched with second-order equation. The adsorption process is monomolecular layer adsorption.Ethanol was desorpted from magnetic Silicalite-1, the results showed that ethanol desorption rate was above 90%, ethanol concentration was between 80% and 90%, and achieve the aim of concentration and recovery of ethaol. The magnetic Silicalite-1 presented a good stability.