近年、膜分離技術は、下水処理の新技術の一つとして広く研究され、応用されています。重力分離、凝固、エマルジョン破壊、油吸収および脱脂、生分解、凝集吸着、イオン交換、その他の従来の分離プロセスなどの他の技術と比較して、この技術には多くの利点があります。例えば、選択性が強く、エネルギー消費量が少なく、適用範囲が広く、環境に優しく、設備が簡単で、操作が簡単などです。油水分離膜は、材質によって有機膜と無機膜に分けられます。有機膜は、科学研究や商業分野で幅広い用途があります。有機膜と比較して、無機セラミック膜は化学的および熱的安定性が強く、汚れに対する耐性と耐圧性に優れ、清掃が容易で、機械的強度が高く、寿命が長いため、油中水エマルジョン分離にセラミック膜を使用することは大きなトレンドです。疎水性改質により、セラミック膜の油に対する濡れ性が向上し、油中水エマルジョンの分離効率が向上し、セラミック膜の化学的安定性と耐久性が向上します。
油中水（W/O）エマルジョンシステムの形態は、水が小さな液滴の形で油に分散していることです。膜分離中の膜汚染は、使用時間の延長とともに透過流束と保持率の低下を招き、膜の耐用年数を短縮し、膜分離技術の応用を制限します。セラミック膜表面の改質により、膜の特定の選択性と分離効果が向上し、膜表面と不要な供給分子との相互作用が減少し、膜汚染がある程度軽減されます。したがって、油中水エマルジョンの分離では通常、疎水性フィルムが選択されます。これにより、膜表面の疎水性と親油性の特性を利用して、油滴は通過し、水滴は捕捉され、油水分離の効果が得られます。
セラミック膜表面の疎水性改質
セラミックフィルム表面の疎水性改質は、通常、疎水性材料を組み合わせたり接着したり、より低い表面エネルギー、適切な粗さおよび表面構造を選択したりすることで実現されます。たとえば、シランまたはチオールを使用して表面の化学特性を付与したり、ミクロンまたはナノ構造を導入してより粗い表面を得たり、フィルム表面の疎水効果を改善して分離性能を高めたりします。
セラミック膜表面の疎水性改質には、含浸法、ゾルゲル法、化学蒸着法の 3 つの一般的な方法があります。
01. ディップ法
Impregnation method (Impregnation method) does not require special equipment, just the original ceramic film directly immersed in hydrophobic substance solution, the method is simple and direct, easy to operate, low cost. The hydrophobic modification of ceramic membrane surface is carried out by immersion method, which usually uses the functional group of hydrophobic substance to connect with the hydroxyl group on the ceramic membrane surface through condensation reaction.
Taking siloxane as a modifier for example, the operation steps of the impregnation method are as follows: dissolve the organosilane in water or ethanol and hydrolyze it to obtain a reactive silanol solution; When the pre-treated ceramic membrane is immersed in the solution, the reactive silane molecules can be adsorbed on the surface of the membrane, and the hydrophobic membrane can be obtained.
Hydrophobic effect is the result of the joint action of surface roughness and surface energy. In the study of hydrophobic modification of ceramic film, it is usually first to provide a certain rough micro-nano structure on the surface of ceramic film, and then modify it with low surface energy. In addition to the modification with silane coupling agent, mercaptan is also the preferred material to reduce the surface energy of the film.
In summary, the operation and steps of hydrophobic modification of the surface of ceramic film by impregnation method are relatively simple, and are greatly affected by the type of modifier, the concentration of modifier, the impregnation time, the number of impregnation times and the roughness of the surface of ceramic film. In addition, because the number of substances with low surface energy that react depends on its own concentration and the number of hydroxyl groups on the surface of ceramic film, Therefore, the method also has a great dependence on the reactive hydroxyl group on the surface of the ceramic membrane.
02. Sol-gel method
Sol-gel technique uses compounds containing highly chemically active components as precursors, and mixes these raw materials uniformly in the liquid phase. After chemical reactions such as hydrolysis and condensation, a stable transparent Sol system is formed in the solution. The sol is slowly polymerized among aged colloidal particles to form a gel with a three-dimensional network structure. The gel was dried and sintered to produce molecular and even nanostructured materials.
The hydrophobic modification of ceramic membrane by sol-gel method can form a large rough structure on the surface of the membrane, and can directly bind low surface energy chemicals. However, the early introduction of organosilane into the sol solution may lead to the formation of large volume polymers, resulting in poor modification effects.
Compared with other methods, sol-gel method can prepare a stable hydrophobic surface with good separation effect, but it takes a long time to prepare the sol solution, and macromolecular polymers may be formed in the process, which affects the modification effect. In general, secondary sintering is required after the completion of coating, and the process is more complicated. In addition, excessive temperature during secondary sintering will destroy the structure of the film, reduce the hydrophobicity and stability of the film, and the aperture of the modified film will decrease with the increase of the number and time of sol-gel coating. In addition, the sol has an important effect on the formation of colloid in the process of colloid preparation, and then affects the film forming quality. Coating time and times, ambient temperature and humidity, heating rate, calcination temperature and calcination time all have a great influence on the subsequent coating drying process. At present, the process can be simplified by reducing the sintering steps at high temperature, forming a rough structure on the surface of the film at one time and combining with low surface energy materials, so as to reduce the damage of the film structure at high temperature.
03 Chemical vapor deposition method
chemical vapor deposition (CVD) uses gas phase reactants deposited on the substrate surface to form a solid film with specific chemical properties. The method has the advantages of controllable film composition, good film repeatability, uniform film layer, wide application range, no restriction on the shape of the substrate and no damage to the substrate material, and is an effective method to change the surface properties and microstructure of the film. For hydrophobic modification of the ceramic film using this method, the ceramic film needs to be placed in a closed container and heated at the boiling point temperature of the organosilane for a long time. The organosilane vapor is passed through to react with the hydroxyl group on the surface of the ceramic film, and the reaction principle is the same as that of the impregnation method.
Under normal circumstances, in order to make the organosilane reagent can be fully utilized, it is necessary to select a closed container with a size similar to the ceramic membrane, so that the contact and reaction of organosilane vapor with the ceramic membrane can be maximized.
化学蒸着（CVD）は、薄膜表面にマイクロナノ粒子やナノロッドを作製し、秩序だった微細構造を形成するための好ましい方法です。化学蒸着法で改質した疎水性セラミック薄膜は、薄膜層が均一で、安定性が良好で、応用範囲が広いなどの利点がありますが、同時に、疎水性薄膜の厚さが薄く、機械的性質が不十分で、外部衝撃により亀裂や気泡などの欠陥が発生しやすいという欠点があります。水滴や汚染物質が亀裂から薄膜に浸透し、薄膜の内部構造を破壊し、薄膜の疎水性と安定性を低下させます。堆積反応に関与する有機シランの中には毒性のあるものもあり、人体や環境に害を及ぼします。また、この方法では反応温度が高く、それに伴う高エネルギー消費と高コストにより、実際の工業生産への応用が制限されます。
