- 學位論文
表面改質對PHEMA/PVDF滲透蒸發膜分離乙酸乙酯水溶液效能之影響
Effect of surface modification on PHEMA/PVDF pervaporation membrane performance for separating aqueous ethyl acetate mixtures
摘要
本研究首先利用旋轉塗佈技術，將聚甲基丙烯酸-2-羥基乙酯 Poly ( 2-hydroxyethyl methacrylate ) (PHEMA)塗佈在非對稱性的聚偏二氟乙烯( PVDF ) 薄膜表面上，製備S-PHEMA/PVDF複合薄膜，應用在滲透蒸發分離乙酸乙酯水溶液。為了提升透過量，研究中添加PVP至PVDF鑄膜液中作為造孔劑，當PVP添加5wt%時可得最高通量之基材。為了改善複合膜界面之貼合性，本研究利用臭氧誘導接枝聚合法，將HEMA接枝在PVDF膜表面製備HEMA-g-PVDF薄膜。經ATR-FTIR鑑定及對水接觸角測詴，確認接枝反應成功進行；進ㄧ步探討臭氧處理時間及單體濃度對接枝密度之影響。由SEM圖發現，S-PHEMA/PVDF薄膜因塗佈層與基材間的親合性不佳，導致PHEMA無法均勻的披覆在PVDF上形成緻密層；而S-PHEMA/HEMA-g-PVDF則能夠改善此缺點，成功製備具有緻密選擇層的複合膜。 研究中探討，接枝密度、塗佈溶液的濃度以及旋轉塗佈轉速對於滲透蒸發效能之影響；隨接枝密度增加，選擇性增加，透過量下降，顯示PHEMA接枝層有抑制膨潤現象的效果；隨塗佈溶液濃度增加，選擇層厚度增加，透過量下降，而透過端水濃度先上升後持帄。隨著轉速提高，透過量增加，而透過端水濃度持帄；結合SEM與可變單一能量慢速正子 ( VMSPB ) 光譜儀分析後證實，轉速越高選擇層的結構會越緻密且越薄。結果指出，此S-PHEMA/HEMA-g-PVDF II 展現高的分離效能，在25 OC下，針對進料為98 wt%的乙酸乙酯水溶液分離時，其透過量為430 g/m2h，選擇比為1830。由結果得知，較佳之製膜條件為: 接枝密度 > 2.4 mg/cm2、塗佈溶液濃度5wt%及轉速為6000 rpm。此研究選擇較佳條件製備之薄膜，探討進料組成以及操作溫度對於滲透蒸發效能之影響。
並列摘要
This study is the first to use spin-coating technique to fabricate composite membranes by applying a poly(2-hydroxyethyl methacrylate) (PHEMA) solution as a thin film on the surface of an asymmetric polyvinylidene ( PVDF ) membrane ( S-PHEMA/PVDF ). These composite membranes were applied for the pervaporation separation of an ethyl acetate/water mixture. To promote the permeation rate, pore-forming agent PVP was added to the PVDF casting solution. We obtained a PVDF substrate with the highest flux when the amount of PVP was 5 wt%. To improve the composite membrane interfacial adhesion, a PVDF membrane surfaced-grafted with HEMA ( HEMA-g-PVDF ) prepared by means of ozone-induced graft polymerization. Attenuated total reflectance Fourier transform infrared ( ATR-FTIR ) spectroscopy and contact angle measurements confirmed the success of the graft polymerization reaction. Furthermore, the effect of ozone treatment time and monomer concentration on grafting density was investigated. From the scanning electron microscopy ( SEM ) analysis, the S-PHEMA/PVDF composite membrane was shown to have a dense skin layer with uneven film coating, indicating a poor compatibility between PHEMA and neat PVDF. This shortcoming, however, was improved in the case of the S-PHEMA/HEMA-g-PVDF composite membrane with a uniform dense active layer, demonstrating a good compatibility between the substrate and the thin layer of film coating. Effects of grafting density, coating solution concentration, and spin coating speed on pervaporation performance were studied. Increase in grafting density resulted in increased selectivity and decreased permeate rate, which illustrated that PHEMA graft layer could inhibit the effect of the swelling phenomenon. Increase in coating solution concentration led to increased thickness of the active layer, decreased permeation rate, and increased water concentration in the permeate at first but it then leveled off. Increase in spin coating speed caused the permeation rate to increase but maintained the concentration of water in the permeate. SEM and variable IV monoenergy slow positron beam ( VMSPB ) analyses confirmed that the active layer became denser and thinner when the spin coating speed increased. Results indicated that S-PHEMA/HEMA-g- PVDF showed high pervaporation efficiency at 25 oC for separating a feed solution of 98 wt% ethyl acetate aqueous solution, giving a permeation rate of 430 g/m2h and a separation factor of 1830. Analytical results gave the following best conditions for preparing a composite membrane: grafting density was about 2.5 mg/cm2, concentration of coating solution was 5 wt%, and spin coating speed was 6000 rpm. Using the composite membrane prepared at these best conditions, the effects of feed concentration and operating temperature on pervaporation performance were investigated.