- 學位論文
聚二甲基矽氧烷/聚偏二氟乙烯複合薄膜中 添加劑對滲透蒸發效能之影響
Effects of additive on pervaporation performance of polydimethylsiloxane/ polyvinylidene fluoride composite membranes
摘要
本研究係以非對稱PDMS複合膜進行乙醇濃度為12 wt.%之醇水混合液進行滲透蒸發醇水分離研究，該複合薄膜(添加劑/PDMS/PVDF)係以聚偏二氟乙烯(polyvinylidene fluoride, PVDF)多孔薄膜為支撐基材，將添加不同添加劑之聚二甲基矽氧烷(polydimethylsiloxane, PDMS)混合液塗佈為緻密表層而得。膜之組成成分對滲透蒸發性能之影響，係藉由鑄膜液濃度、上游端之進料溫度、 添加劑之親疏水性及不同醇類等參數之變化進行探討。成膜之截面與表面型態採SEM進行觀測；而奈米添加劑則以TEM觀測之。接觸角、ATR-FTIR光譜及EDX光譜等儀器分析，則分別用以驗證成膜之表面親疏水性質、交聯作用、分子間作用及膜組成元素等性質。都卜勒展寬511KeV -射線用以鑑定PDMS膜層；而PDMS複合膜(PDMS/7048交聯劑/催化劑; 100/25/3)在不同溫度下之自由體積孔徑則以正子湮滅壽命光譜技術加以解析。 滲透蒸發結果顯示，隨著PDMS濃度增加，透過端乙醇濃度亦呈增加趨勢，意味非對稱PDMS/PVDF薄膜具有優選醇之性質；此外，隨著PDMS濃度增加，透過端乙醇濃度亦呈增加趨勢，意味非對稱PDMS/PVDF薄膜具有優選醇之性質；然而，相對於透過濃度，其透過流率呈現出trade-off 之模式。VMSPB分析結果顯示，鑄膜液之PDMS濃度較高者，所形成之緻密膜層越厚，因而透過端呈現較高之乙醇濃度與較低之透過流率；亦即，當PDMS鑄膜液濃度由25 wt.%提升至40 wt.%時，透過端乙醇濃度可由18.4 wt.%提升至26.4 wt.%；相對地，其透過流率則由1638 g/ m2 h 降至613 g/ m2 h。PDMS亦對不同醇類進行選擇性之評估，其中以含碳量較高之醇類作為進料端之醇水混液者，可在透過端取得較高之乙醇濃度。在不同溫度下進行PALS解析，3-1之值由25℃之1.6 ns變化為70℃之1.0 ns；3-2之值則相對應由3.1 ns變化為3.4 ns，此顯示出高分子膜材之自由體積孔徑歷經了變化；亦即，隨著溫度增加，小孔徑自由體積受到較大自由體積擴開之影響而呈現出擠壓縮小之結果，此現象亦呼應了薄膜在滲透蒸發透過選擇性能之展現。添加奈米矽、341NHA沸石與PTFE粒子所製備之PDMS複合膜經以接觸角量測儀量測，其結果與滲透蒸發性能比對，其中以含10 wt.%PTFE奈米粒子複合膜之接觸角達112.8者為最高，其透過端所展現之乙醇濃度(35wt.%)亦為最高；相反地，含矽粒子所測之接觸角96者為最小，甚至比純PDMS膜者為小，而所測得之乙醇透過濃度亦呈最小，證實疏水性膜材具有優選乙醇透過之性能，反之亦然。據此，採用三種表面經不同官能基團修飾之疏水fumed silica奈米粒子為添加劑，經分別製備出PDMS複合膜，添加劑包括R974、R812與R202 fumed silica粒子，其表面具有不同之短鏈烷基官能團而呈現疏水特性。含有fumed silica粒子PDMS複合膜之優選乙醇特性均較原始PDMS膜材為佳，各種fumed silica粒子含量在10 wt.%者，在25℃滲透蒸發性能測試，其乙醇透過濃度分布高達32~34 wt.%之間，展現比原始PDMS膜高一倍之乙醇透過濃度；當以70℃測試，所有膜材均呈現較低溫測試者為高之乙醇透過濃度，其中以含10 wt.%R907 系列展現乙醇透過濃度達43 wt.%為最高。至於透過流率，高溫測試之透過流率相對較高，但除了含量為 0.5 wt.%R907系列，其在25 與70℃之透過流率分別達1301與8976 g/ m2 h， 展現比純PDMS膜為高之值外， 其它系列所測試者均較純PDMS膜為低。含10 wt.%R907粒子之PDMS複合膜經45天期之高低溫長效操作測試，該膜材之滲透蒸發性能呈現穩定性，證實具有抗溶脹特性。
並列摘要
The separation of ethanol-water mixtures with ethanol content of 12 wt.% was studied on asymmetric polydimethylsiloxane (PDMS)-based composite membranes, composed of an additive-blended PDMS dense layer coated on a porous polyvinylidene fluoride (PVDF) surporting substrate. The influence of participants on pervaporation performance was examined with respect to changing the content of casting solution, the hydrophilic/hydrophobic property of the additives, temperature of the feed, and type of alcohols. The cross-sectional and surface morphologies of the as-prepared membranes were observed using scanning electron miscroscopy (SEM), and nanoparticles used as additives were observed using transmission electron microscopy (TEM). The membranes were extensively characterized by contact angle meter, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and energy-dispersive X-ray (EDX) spectroscopy respectively, to verify surface hydrophilicity, crosslinking, intermolecular interactions, and constituents of the membranes. Doppler broading of the annihilation 511 KeV gamma-line was performed to identify the formed PDMS layer. The PALS (positron annihilation lifetime spectroscopy) technique was also carried out at different temperatures to measure the free-volume hole sizes of the membrane prepared based on a set of PDMS solution/7048 crosslinker/catalyst (100/25/3). The results on pervaporation measurements indicated that the ethanol concentration on permeate side increases with increasing PDMS content of casting solution, implying a preferentially ethanol-selective property to the asymmetric PDMS/PVDF membranes; however, its permeate rate is in response to a trade-off behavior. Results of VMSPB (variable monoenrgy slow positron beam) showed that a thicker dense layer was formed as the casting solution contains a higher PDMS content, which turns out a higher ethanol concentration at permeation side associated with a lower permeation rate i.e., when the PDMS content of 25 wt.% increases up to 40 wt.%, the ethanol concentration increases from 18.4 wt.% up to 26.4 wt.%, and contrarily, the permeation rate decreases from 1638 g/m2 h down to 613 g/m2 h. Ethanol-selectivity evaluation on the PDMS membrane was also carried out in terms of alcohols having different carbon number. It was found that the higher the carbon number of the alcohol in the aqueous solution as the feed, the higher the alcohol concentration at the permeation side. The PALS results obtained by measuring at different temperature presented that 3-1 varied from 1.6 ns ( 25℃) to 1.0 ns (70℃) associated with a change of 3-2 form 3.1 ns to 3.4 ns. It implied that the polymer matrix was subjected to a change on the free-volume pore size induced by temperature, i.e., a shrinking of smaller pore arisen from an expanding of larger pore owing to temperature increasing. These results were found to be well correlated to the perm-selectivity of the resultant membranes on pervaporation. Additive/PDMS-based composite membranes prepared respectively by blending nanosized silica, 341NHA zeolite, and PTFE particles, were evaluated using pervaporation in terms of enthanol perm-selectivity by means of contact angle. Results obtained from the contact angle measurements indicate that the resultant membrane containing 10 wt.% PTFE particles presents the highest value (112.8) among them and it turns out exhibiting the highest ethanol concentration (35 wt.%) on the permeation side. Contrarily, the resultant membrane containing silica particles having the lowest contact angle of about 96 that is lower than that of the pristine PDMS membrane, performs the lowest ethanol-selectivity. It confirms that the resultant membrane having hydrophobic property behaves preferentially ethanol-selectivity and vice versa. Accordingly, three types of hydrophobic fumed-silica particles that were surface-modified with different functional groups were blended respectively with PDMS for further evaluation on pervaporation. R974, R812 and R202 fumed silica particles having different short chain alkyl groups extruding outward present intrinsically hydrophobic property. Filling the PDMS-based membrane with different fumed silica particles performed in ethanol-selectivity is superior to its pristine one. Based on the fumed silica content of 15 wt.% relative to PDMS, a maximum effect of ethanol concentration in all series measured at 25℃ is as high as 32~34 wt.% which is the double of the pristine one. When they were measured at 70℃, it was found that all of silica-blend series exhibit higher ethanol-selectivity, and so does the pristine PDMS membrane. The highest ethanol concentration up to 43 Wt.% was obtained based on the R907 particle with the content of 10 Wt.%. As regards the permeation rate, all of PDMS-based membranes present a higher value when the pervaporation were performed at higher temperature. Except for the R907 series with silica content of 0.5 Wt.% showing the permeation rates up to 8976 g/m2 h (70℃) and 1301 g/m2 h (25℃), all of silica-blended composite membranes exhibit a much lower permeation rate than that of pristine one. Results obtained from the research of a long term test on pervaporation, the silica-fumed (R907) PDMS-based composite membranes can stand against swollen at both 25℃ and 70℃ by showing stability on the perm-selectivity performance for more than 45 days.