製備聚醯胺奈米過濾複合膜回收廢水中弱酸與四甲基銨離子之研究

Abstract

無機弱酸如硼酸、矽酸以及磷酸是工業上經常使用的重要原料，這些工業所排放的廢水必須妥善處理。而半導體產業經常使用四甲基氫氧化銨作為晶圓製程的顯影劑，其高毒性的四甲基銨離子具有純化回收的工業價值。因此，本研究以piperazine (PIP)作為水相單體，與有機相單體trimesoyl chloride (TMC)在PSf基材膜表面進行界面聚合反應，製備聚醯胺奈米過濾複合膜，分別探討弱酸水溶液與四甲基氫氧化銨(TMAH)水溶液在不同條件下的分離效能。 弱酸在水溶液中的解離程度取決於其pKa值。在鹼性環境下(i.e., pH > pKa)，弱酸會由中性分子轉變為帶負電荷的陰離子，有利於奈米過濾膜利用道南效應(Donnan effect)對其進行分離。因此，本研究以硼酸、矽酸以及磷酸水溶液作為進料溶液，藉由調整進料溶液的pH值，探討弱酸水溶液在不同pH值條件下的奈米過濾效能，並將實驗結果量化分析，深入分析各條件下弱酸的型態分佈、離子成分及濃度、薄膜表面電位以及滲透壓等參數對實驗結果的影響。藉由這些分析以理解聚醯胺複合膜在不同條件下對弱酸所展現的分離機制與效能。研究後續亦探討改變界面聚合條件對薄膜結構、表面電荷以及弱酸分離效能的影響。 本研究亦探討聚醯胺複合膜對TMAH水溶液的奈米過濾效能。研究中以H2SO4調整進料溶液pH值，利用二價陰離子SO42-更容易受道南效應排斥的特點，並藉由水溶液的電中性原則，提升TMA+阻擋率。研究中探討pH值變化對TMA+分離效能的影響。除此之外，本研究也探討了TMA+離子與一價金屬離子分離的可行性，利用聚醯胺複合膜測試TMA+/Na+混合溶液，探討薄膜在不同pH條件下對TMA+/Na+離子之選擇性。 由弱酸水溶液的研究結果顯示，PIP-TMC/PSf複合膜的阻擋率與通量皆隨著pH值上升而提高，在pH 12時對硼酸及矽酸具有最高的阻擋率，分別為72.1 %及 77.7 %；磷酸在pH 10-12之間具有最高的阻擋率(約96.3 % ~ 96.7 %)；滲透通量在pH 12時約60 LMH。另外，增加有機相單體濃度，在pH 12時可將硼酸與矽酸的阻擋率分別提升至80.1 %及85.0 %，但滲透通量下降至約40 LMH。而提高MPDA在水相單體中的比例，可使複合膜選擇層更加緻密，但阻擋率並未改善。 對於TMAH水溶液，PIP-TMC/PSf複合膜在中性與酸性條件下具有最佳的TMA+阻擋效果，其阻擋率約90.3 % ~ 92.3 %。另外，利用PIP-TMC/PSf複合膜分離TMA+/Na+混合離子，在pH 2時具有最理想的效果，阻擋率分別為RTMA+ % = 91.7 %, RNa+ % = 49.8 %，選擇比SNa+/TMA+ = 6.07，溶液滲透通量為30.9 LMH。

Weak acids such as boric acid, silicic acid, and phosphoric acid extensively employed in various industries, and the wastewater discharged from these industries must be properly treated. In the semiconductor industry, tetramethylammonium hydroxide (TMAH) is commonly used as a developer in wafer processing, and its highly toxic tetramethylammonium ions (TMA+) are necessary for purification and recycling. In this study, piperazine (PIP) as the aqueous monomer reacted with trimesoyl chloride (TMC) organic monomer via interfacial polymerization on the surface of polysulfone (PSf) substrate membrane to prepare polyamide composite nanofiltration membranes, and the resulting composite membranes were used to investigate the separation performance of weak acid solutions and TMAH solutions under different conditions. The dissociation degree of weak acids in aqueous solutions dependent on their pKa values. In an alkaline environment (i.e., pH > pKa), weak acids convert from neutral molecules into negatively charged anions, facilitating the separation via the Donnan effect using nanofiltration membranes. Therefore, this study employs boric, silicic, and phosphoric acid solutions as feed solutions. By adjusting the pH of the feed solutions, the nanofiltration performance of weak acid solutions at different pH conditions is explored. The experimental results are analyzed to comprehensively understand the influence of weak acid species distribution, ionic composition and concentration, membrane surface charge, and osmotic pressure on the separation mechanism and performance of polyamide composite membranes under various conditions. Subsequent research also investigates the impact of altering membrane structure and surface charge through interfacial polymerization on the separation performance of weak acids. This study also investigates the nanofiltration performance of polyamide composite membranes for TMAH solutions. By adjusting the pH of the feed solution using H2SO4 and enhancing the Donnan effect with divalent anions (SO42-) to improve TMA+ rejection. This study examines the effect of pH on the separation performance of TMA+. Additionally, the feasibility of separating TMA+ ions from monovalent metal ions is explored. Polyamide composite membranes were used to test the selectivity for TMA+/Na+ ions under different pH conditions. The results show that the rejection and flux of the PIP-TMC/PSf composite membranes increase with rising pH values. The optimal pH value for nanofiltration of boric and silicic acids is pH 12, the boron rejection is 72.0 % and the silicon rejection is 77.7 %. Phosphate rejection is approximately 96.3 % ~ 96.7 % at both pH 10 and 12. The water flux is around 60 LMH at pH 12. Furthermore, increasing the concentration of the organic monomer can further enhance the rejection of boric and silicic acids to 80.1 % and 85.0 %, but the flux decreases to around 40 LMH. Additionally, increasing the proportion of MPDA in the aqueous monomers results in a denser selective layer of composite membranes, but the rejection does not improve. The PIP-TMC/PSf composite membranes exhibit optimal TMA+ rejection under neutral and acidic conditions, achieving rejection approximately 90.3 % ~ 92.3 %. Additionally, for the separation of TMA+/Na+ ions, the PIP-TMC/PSf composite membranes perform optimally at pH 2, with RTMA+ % = 91.7 %, RNa+ % = 49.8 %, separation factor SNa+/TMA+ = 6.07, and flux = 30.9 LMH.