Perparation Of Membrane For Pervaporation Separation Organic Substance From Aqueous Solution

During the manufacturing process of foods and beverages, the volatile organic compounds (VOC), generally called aroma compounds, which contribute significantly to the flavor, should be seperated to avoid being lost and then added after the heating process to preserve the taste. During the production process of biofuel by fermentation, the butanol in dilute solution should be recovered to lower the product inhibition and ensure the continuous fermentation. The conventional seperation processes, including distillation, extraction, adsorption and so on, surfer from high engrgy consumption, serious environment pollution, great installation cost and poor economic performance. Pervaporation (PV) is a new membrane separation technique to separate liquid and gas mixtures, especially in the use of the separation of homogeneous mixtures such as azeotropic, closing-boiling and dilute concentration mixtures, which are difficult to separate by conventional methods. PV process is based on the different selectivity of membrane materials towards the various components in the mixtures, so the most researches focus on the preparation and modification of the membrane. Organic-inorganic hybrid membranes possess the advantages of polymer and inorganic materials, arousing more and more attentions. But the poor compatibility between these two kinds of materials limit the development of the hybrid membranes, therefore the most researches focus on the improvement of the compatibility.In the present study, two kinds of amphipathic materials were chosen including polyether block amide (PEBA) and polyurethaneurea (HTPB-PU), and incorporated inorganic fillers ZSM-5 to prepare organic-inorganic hybrid membrane. The chemical structure, morphology and stability of these filled membranes were characterized. The effects of ZSM-5 content on swelling degree and pervaporation separation performance of organic compound from dilute solution were investigated. Meanwhile, in order to improve the compatibility between the polymer and the inorganic particles, the ZSM-5 particles were modified by a silane coupling agent vinyltriethoxysilane (VTES) and incorporated into polydimethylsiloxane (PDMS) for the preparation of hybrid membranes. The effect of modification of ZSM-5 on PV performance and character of hybrid membrane were investigated. The main experimental results and conclusions can be listed as followings:(1) The PEBA/ZSM-5 and HTPB-PU/ZSM-5 membranes were prepared for the separation of ethyl acetate and isopropyl acetate from the aqueous solutions by pervaporation respectively. The results indicated that with the incorporation of ZSM-5, the thermal stability and the hydrophobic performance of the membrane increased, while the swelling degree decreased. The ZSM-5 dispersed uniformly in the membrane and the separation factor increased first and then decreased with the increase of the ZSM-5 loading. The PEBA/ZSM-5 membranes containing 10wt% ZSM-5, PEBA/ZSM-5-10, showed the highest separation factor (101.9) at 30 oC with feed concentration of 1.63wt% EA. With the increase of the operating temperature and feed concentration, both the permeation ?ux and separation factor increased. The best PV performance of the PEBA/ZSM-5-10 membranes, separation factor and total ?ux were 185.5 and 199.5g/m2h, respectively with feed concentration of 1.80wt% EA at 50oC. The HTPB-PU/ZSM-5 membranes containing 20wt% ZSM-5, HTPB-PU/ZSM-5-20, showed the highest separation factor at 30oC with feed concentration of 0.37wt% IPAC. With the increase of the operating temperature and feed concentration, both the permeation ?ux and separation factor increased. The best PV performance of the HTPB-PU/ZSM-5-20 membranes, separation factor and total ?ux were 288.7 and 53.2g/m2h, respectively with feed concentration of 0.39wt% IPAC at 60oC.(2) The ZSM-5 particles were modified by a silane coupling agent vinyltriethoxysilane (VTES), and examined by FT-IR, XRD and TGA. The results showed that the silane coupling agent was bonded to the surface of silicalite-1 particles through chemical bonds and the modification did not in?uence the framework of silicalite-1 crystals, which occurred at the surface.(3) The hybrid membranes incorporated with unmodified ZSM-5 particles and VTES modified ZSM-5 particles were prepared, and the pervaporation performances of the hybrid membranes with dilute butanol solutions was investigated. The effects of VTES modified, ZSM-5 content, feed concentration and temperature were studied, the results indicated that as compared with the unmodified hybrid membranes, the PDMS/VTES-ZSM-5 hybrid membranes improved the pervaporation selectivity of butanol effectively. The PDMS/VTES-ZSM-5 membranes containing 10 wt% VTES-ZSM-5, showed the highest separation factor (17.6) at 30oC with feed concentration of 1wt% butanol. With the increase of the feed concentration, the separation factor decreased, while with the increase of the operating temperature, both the permeation flux and separation factor increased. The best PV performance of the PDMS/VES-ZSM-5-10 membranes, separation factor and total ?ux were 22.4 and 139.8g/m2h, respectively with feed concentration of 1wt% butanol at 60oC. As showed in the results, although the PV performance of PDMS/ZSM-5 membranes were lower than that of PDMS/VTES-ZSM-5 membrane, it was better than the pure PDMS membranes, indicating that ZSM-5 particle was good for the separation of the organic compounds.