高性能正渗透复合膜的制备及表征

发布时间：2018-05-04 14:23

本文选题：正渗透 + 复合膜　；参考：《中国科学技术大学》2015年博士论文

【摘要】：正渗透(forward osmosis, FO)技术在常压条件下能利用半透膜两侧溶液渗透压差异,可实现溶液自发分离,在解决水源与能源间的矛盾方面表现出巨大的潜力。然而,长期以来由于高性能FO膜的短缺抑制了该技术的发展,在压力驱动过程中表现优异的渗透膜,却在FO过程中出现严重的内浓差极化效应,导致膜的渗透通量远低于理论值,极大地影响了生产效率和FO技术的实际应用。同时,复合膜皮层粗糙的表面和化学结构增加了膜污染倾向。因此,针对以上问题,开发新型的高性能复合膜,在保持高选择性的同时,减弱内浓差极化的负面影响,提高水的渗透通量,增强膜的抗污性能,成为当前正渗透膜开发的研究热点。共混改性是提高聚合物膜材料性能、拓宽其应用范围的简单、高效的方法。本文通过在常用的膜材料PES中掺入碳纳米管、氮化碳掺杂石墨烯、MMT@SPES等有效地改善了薄膜复合膜支撑层的结构和性质,降低了膜的结构参数,提高了膜的渗透通量,另外,我们还用简单的二次界面聚合法实现了聚酰胺层的化学结构性质、表面形貌及其在正渗透过程中应用性能的转变。主要的研究结果如下： (1)酸化后的多壁碳管在聚吡咯烷酮的辅助下通过溶液混合法分散于PES基质中,经相转化获得多孔膜,以其为基膜制备了复合膜,并用于盐水的分离。结果发现：适当的碳纳米管可增加基膜孔隙率,因碳管贯穿在基质中形成更多的孔道结构,有助于通量的增加,复合膜的截盐率也可达97%,同时,基膜的力学强度并不因形成较多的孔隙发生下降,反随碳管的添加量增加而升高。 (2)成功合成了一种多孔层状材料一氮化碳掺杂石墨烯(CN/rGO)并用作复合膜支撑层的改性剂,在PES基质中添加0.5wt.%的CN/rGO,所得复合膜在2M氯化钠为提取液,去离子水为进料时,可获得高达41.4L/m2h的水通量,比空白膜高20%,这一结果归因于膜结构的改善和基膜孔壁亲水性的增加。 (3)利用无机粒子-蒙脱土(MMT)与亲水性聚合物-磺化聚醚砜(SPES)间的静电作用,减少了亲水性聚合物在非溶剂相转化过程中的损失,FT-IR和XPS分析结果证明,MMT把更多的SPES锚定在PES基质中。我们发现添加了MMT@SPES的多孔膜,由于润湿性能的增加,纯水透过系数从PES膜的60.9LMH/bar提升到460LMH/bar,而膜孔径维持在适合形成聚酰胺层的300kDaMWCO以内。用以上多孔膜作基膜的正渗透复合膜,以PES/MMT@SPES(40)为例,其在FO模式下,水通量比基于PES/SPES所得的复合膜通量提高了4倍,而盐的反向渗漏通量减小了一半,这一结果可归因于混合基质的基膜具有更强的润湿性和更窄的孔径分布。 (4)通过分别用乙二胺(EDA)和乙二胺乙磺酸钠(SEA)水溶液浸渍初生的芳香聚酰胺(PA)层,在复合膜表面发生原位二次界面聚合(SIP)反应,我们系统考察了二次界面聚合及所用浸渍单体对膜的性质及应用性能的影响,发现EDA改性可提高膜的抗污性能,SEA则在不影响膜的选择性的前提下,正渗透水通量增加了2倍,但尽管其表面更加平滑和亲水,抗污能力却发生了下降。这是因为较高的渗透的初始通量也加剧了膜污染的程度。虽然膜表面性质与膜污染存在一定的联系,但初始通量却是影响膜污染的主要因素。
[Abstract]:Forward osmosis (FO) technology can make use of the difference in osmotic pressure on both sides of the semi permeable membrane under normal pressure, which can realize the spontaneous separation of the solution and show great potential in solving the contradiction between water and energy. However, for a long time, the shortage of high performance FO film inhibits the development of this technology, and in the process of pressure driving. The present excellent permeable membrane has serious internal consistency polarization effect in the process of FO, which leads to the permeation flux of the membrane far below the theoretical value, which greatly affects the production efficiency and the practical application of FO technology. At the same time, the rough surface and chemical structure of the composite membrane increase the tendency of membrane fouling. The performance composite membrane, while maintaining high selectivity, reduces the negative influence of the internal consistency polarization, improves the permeation flux of water and enhances the anti fouling performance of the membrane. It has become a hot spot in the current research of the development of the positive permeable membrane.
Blending modification is a simple and efficient method to improve the properties of polymer film materials and broaden its application range. In this paper, the structure and properties of the support layer of the film composite film are effectively improved by adding carbon nanotubes, carbon nitride doped graphene and MMT@SPES in the commonly used membrane material PES, and the structure parameters of the membrane are reduced and the membrane permeability is improved. In addition, we have also realized the chemical structure properties of the polyamide layer, the surface morphology and the transformation of its application performance in the process of positive Osmosis with a simple two interface polymerization method. The main results are as follows:
(1) the multi wall carbon tube after acidification is dispersed in the PES matrix by solution mixing under the aid of Polypyrrolidone ketone, and the porous membrane is obtained by phase transformation. The composite membrane is prepared as the base film and used in the separation of salt water. The results show that the proper carbon nanotubes can increase the pore rate of the base film, and the carbon tube can form more Kong Daojie in the matrix. With the increase of flux, the salt cutting rate of the composite membrane is also up to 97%. At the same time, the mechanical strength of the base film does not decrease with the formation of more pores, but increases with the increase of the amount of carbon nanotubes.
(2) a porous layered material, carbon nitride doped graphene (CN/rGO) was successfully synthesized and used as a modifier for the composite membrane support layer. The CN/rGO of 0.5wt.% was added to the matrix of PES. The composite membrane was extracted from 2M sodium chloride and the deionized water was used as the feed. The water flux of up to 41.4L/m2h was obtained, which was higher than that of the blank film. The result was attributed to the result of this result. Improvement of membrane structure and increase of hydrophilicity of basement membrane.
(3) using the electrostatic action between the inorganic particle montmorillonite (MMT) and the hydrophilic polymer sulfonated polyethersulfone (SPES), the loss of the hydrophilic polymer during the non solvent phase transformation is reduced. The results of FT-IR and XPS analysis show that MMT has anchored more SPES in the PES matrix. We found the porous membrane added to the MMT@SPES, due to the wettability. The permeability of pure water is increased from the 60.9LMH/bar of the PES film to 460LMH/bar, and the membrane pore size is maintained within the 300kDaMWCO suitable for forming the polyamide layer. The positive permeable composite membrane with the above porous membrane as the basement membrane, for example, in PES/MMT@SPES (40), is 4 times higher than the flux of the composite membrane based on PES/SPES in the FO mode, while the salt flux is higher than that of the PES/SPES. The reverse leakage flux is reduced by half. This result can be attributed to the stronger wettability and narrower pore size distribution of the substrate.
(4) by impregnating the primary aromatic polyamide (PA) layer with ethylenediamine (EDA) and ethylenediamine sodium sulfonate (SEA) aqueous solution respectively, the in-situ two interfacial polymerization (SIP) reaction occurred on the surface of the composite membrane. The effects of two interfacial polymerization and the impregnated monomers on the properties and application properties of the membrane were systematically investigated. It was found that the EDA modification could improve the membrane. The flux of positive permeable water increased by 2 times without affecting the selectivity of the membrane, but in spite of the smooth and hydrophilic surface of the SEA, the anti fouling ability decreased. This is because the initial flux of high permeability also aggravates the degree of membrane fouling. Although the membrane surface properties are related to the membrane pollution, the initial flux has a certain relationship with the membrane fouling. Flux is the main factor affecting membrane fouling.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ051.893

【共引文献】