| As a developmental research with great prospect, membrane separation technology has been widely applied in the modern industry. And as known to all, pervaporation is a new type of membrane separation technology which has many advantages over other techs in the separation of liquid mixtures, such as high efficiency, low energy consuming, simple operation process, etc. Particularly, it is very suitable for the separation of homogenous mixtures such as closing-boiling and isomeric mixtures, which are usually difficult or impossible to be separated effectively.PDMS has been generally regarded as a very nice and comprehensive alcohol-prior penetration membrane material, but unfortunately the material just has a relatively low mechanical strength is also very poor; consequently, many scholars have tried their best to improve its mechanical strength and separation ability. On the other hand, Fumed silica is a kind of strength supplement, and it has an ideal property of hydrophilicity because of the hydroxyl groups absorbed on the surface, which leads to a difficult diffusion when mixed with organic phase and meanwhile affects its application prospect, so it is necessary to enhance its compatibility in the organic phase via surface hydrophobic modification and thus extend is application field.In this paper, fumed silica was modified to possess hydrophobic property by organic wet method taking hexamethyldisiazane (HMDZ, modifier) and dimethyl- diethoxysilane (co-modifier) as modifiers. The appraisal of modification effect was investigated by measuring the surface hydroxyl groups. The influences of different organic solvents for the modification results were respectively studied, and particularly the impacts of temperature and reaction time when used toluene as solvent were discussed, and a preferable preparation process condition was obtained by using toluene as solvent, at 110℃for 90 min.The evaluation of the various surface modifications of silicon was finally characterized by infrared spectrum analysis and TEM. It was found that a certain amount of polymer had been attached to the surface of the fumed silica, which conversely reduced the original content of SiO2. And settlement experiment of water as solvent showed the modified fumed silica possessed high hydrophobic property.The current PDMS/PET composite membranes were prepared by filling PDMS membrane with fumed silica and modified fumed silica on PET membrane. The tensile strength, physical morphology, molecule structure and thermal resistant performance of the as-prepared composite membranes were investigated by WSM-5KN. TGA. FT-IR and SEM. And further the effects of feed temperature, feed concentration, vacuum, content of modified fumed silica on the pervaporation performance of ethanol/water solutions were also examined.It was shown from the results that the thermal resistant performance of the modified membrane was significantly improved and it increased as the modified fumed silica increasing. Its tensile-strength was increased from 1.5 MPa to 7.4 MPa compared with pure PDMS. And the SEM results indicated that the modified hydrophobic fumed silica could be better distributed in the PDMS membrane than ordinary silica.It could be obtained from the pervaporation results that the permeation flux of the as-prepared membrane was in direct ratio with the gradual increase of feed concentration, feed temperature and vacuum, while the separation factor appeared to increase with the raising of vacuum and the feed concentration at first and then declined as well as feed temperature, and further the related relationship between component flux and temperature could be explained by Arrhenius equation. Otherwise the peak value of the membrane separation factor seemed to constantly appear in advance. |
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