Investigation On The Preparation And Separation Performance Of Organics/water Mixture Pervaporation Membranes

Pervaporation technology is a new type of membrane separation technology, which has developed for nearly two decades. Pervaporation has such advantages of simple operation, low energy consumption and no introducing a third component, so it has been widely recognized by people. With the development of pervaporation technology,the conventional membrane material for separating organics/water has gradually exposed lots of shortcomings, for example, small mechanical strength, poor stability or low separation performance, which has limited them to meet the actual needs of industrial production. Therefore, membrane materials which have high separation performance, good mechanical strength and stability have gradually become the focus of hot spots. This thesis is aim to use the excellent characteristics of new materials to prepare a few new types of pervaporation membranes which could be used in separating organics and water.( 1) Firstly, the polymerized ionic liquid(PVMHF) was synthesized by using ionic liquid of VMHF, DMSo as solvent and AIBN as initiator. Then the PVMHF and VMHF were studied using fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis(TGA), results indicated that vinyl of VMHF was fully polymerized and the PVMHF had better thermal stability in the range of 30~100℃.Secondly, PVMHF was dissolved in DMSo to give the casting solution, and then put the casting solution in vacuum drying oven to prepare PVMHF membrane. The PVMHF membrane showed a smooth and dense surface by scanning electron micrographs.Finally, the PVMHF membrane was used for swelling and pervaporation experiments for ethanol-water mixture. Results showed that the anion and cation of PVMHF membrane first contacted with water, which maked PVMHF membrane exhibit permeability to water priority. So the PVMHF membrane showed good effect of dehydration on high concentration of ethanol solution. In conclusion, PVMHF membrane exhibited the best separation effect for 97.5% ethanol solution at 45℃, with the flux of 158.67g·m-2·h-1 and the separation factor of 242.61.(2)ZIF-8 nanocrystals were synthesized using methanol as solvent, and then they were characterized by X-ray diffraction(XRD). Results showed that the XRD diffraction peak spectra of synthesized ZIF-8 well matched with the standard analog ZIF-8diffraction peak spectra, which proved that synthesized ZIF-8 nanocrystals had a good crystallinity. Secondly, mixed matrix membranes(MMMs) of TPU loaded with differentcontent of ZIF-8 nanocrystals were prepared and characterized by FTIR, TGA, SEM and swelling degree measurement. Results of FTIR and SEM suggested that ZIF-8nanocrystals could be well compatible with TPU, and the swelling experiment demonstrated that ZIF-8 showed high affinity to ethyl acetate. After that, MMMs were further subjected to pervaporation separation of race ethyl acetate in water, and the pervaporation properties were investigated at different temperatures, different feed concentration and various ZIF-8 content. Results showed that the flux and separation factor increased with the growth both operating temperature and feed concentration.With ZIF-8 content increasing, the flux and separation factor gradually increased, but once its content exceed 30wt%, they would decrease. In other words, the flux and separation factor reached their maximum 155.283g·m-2·h-1and 3.095, when ZIF-8content was 30wt%.(3)Cross-linked EVOH membranes were prepared by the method of chemical cross-linking with high crystallinity EVOH as membrane material. Then cross-linked EVOH membranes were characterized by TGA, SEM and swelling degree measurement.Results of SEM showed that cross-linked EVOH membranes had smooth, dense surface,and there was no big hole on it. TGA test results indicated that cross-linked EVOH membranes began pyrolysis slowly at 100℃, and pyrolysis significantly after 350℃.Moreover, the cross-linked EVOH membranes were further studied in detail to understand the effect of variations in GA content, feed concentration and operating temperature on its pervaporation performance. Results showed that cross-linked EVOH membranes were a kind of hydrophilic membrane, which were preferred to water and produced permeate concentrated in water. When GA content increased, the separation factor increased continuously, but the flux increased first and then decreased. The flux increased slightly but the separation factor decreased obviously with the growth of feed concentration, which proved that the cross-linked EVOH membranes had an excellent selectivity at lower feed concentration. The flux of permeation was found to increase obviously, while the selectivity to a little decrease with the temperature rising, which demonstrated that the cross-linked EVOH membranes had an excellent permeability at higher temperature. In a word, the membrane(GA/EVOH=1.5) represented the best pervaporation performance when the ethanol concentration was 95wt% at 70℃,with the flux of 382.264 g·m-2·h-1 and the separation factor of 56.72.