超疏水聚酰亚胺纤维膜的制备及其膜蒸馏应用实验研究

发布时间：2018-05-11 01:38

本文选题：膜蒸馏 + 表面修饰　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：膜蒸馏(MD)作为一种热驱动的新型膜分离技术,在海水淡化、废水处理和浓缩减排等方面都有着广泛的应用前景,但是传统的膜蒸馏用膜,如聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)和聚丙烯(PP)等,都存在膜通量较低、疏水效果差、膜孔容易被堵塞和膜表面容易被润湿等问题。因此,开发出一种膜通量大、疏水性能好、盐分截留率高且运行稳定的膜蒸馏用膜,对膜蒸馏工业化起着极为重要的推进作用。本论文以双重仿生超疏水化的改性方法为核心,结合静电纺丝制膜技术,制备出超疏水聚酰亚胺纳米纤维膜作为膜蒸馏用膜,应用于直接接触式膜蒸馏(DCMD)实验,研究不同实验条件下膜蒸馏效能,并对改性后聚酰亚胺(PI)纤维膜进行应用潜能分析。膜蒸馏用膜的微孔结构和疏水性能决定了膜通量和盐分截留率的大小,目前传统用膜存在孔隙率低、孔道曲折等缺陷,因此考虑使用静电纺丝技术来制备纤维直径小、孔隙率高、比表面积大且纤维交联互通的基膜;另外,对于基膜的疏水改性是延缓蒸馏过程中发生膜润湿的有效措施之一,目前获得疏水膜结构的方法有原位方法和后处理法,本文采用的是在基膜上进行后处理,首先利用多巴胺(DA)与聚乙烯亚胺(PEI)在水中能够发生交联反应,形成一层仿生物胶的带电层(C-PDA/PEI),在不破坏PI纤维膜表面的同时构建了正电荷粘性层;然后将带有负电的二氧化硅纳米颗粒(Si O2 NPs)通过静电吸附组装到纳米纤维表面,重新构造膜表面结构,加大了纤维表面的粗糙度;最后通过氟化来降低纤维膜的表面能,形成仿荷叶表面的超疏水聚酰亚胺多孔纤维膜(152°)。将改性后的PI膜进行了膜蒸馏测试,与改性各阶段的PI膜和不同孔径的PTFE膜进行了对比,可以看出改性后的PI膜不但在稳定性上占据优势,而且膜通量和盐分截留率也比相同孔径PTFE膜高;为了测试膜的抗污染性能,分别将改性后的PI膜应用于处理含有表面活性剂(SDBS)、腐殖酸(HA)、甲基蓝染料作为有机污染物代表的Na Cl盐水中,记录实验过程中膜通量和电导率随时间的变化情况,证实了改性后的PI膜具备良好的耐污染性能。接着将改性后的PI膜进行反渗透(RO)浓水的浓缩减量实验,发现在进料液的体积浓缩到原来的1/4后,还能保持较高的膜通量的盐分截留率,说明改性后的PI膜能够在进料液浓度很高的情况下保证一定的抗污染和自洁性能;最后将改性后的PI膜进行了模拟海水淡化的膜蒸馏实验,对膜蒸馏海水淡化工艺进行技术评价和经济分析,为膜蒸馏工艺在海水淡化中的用膜选择提供了另一种可能。
[Abstract]:As a new heat-driven membrane separation technology, membrane distillation (MD) has a wide application prospect in seawater desalination, wastewater treatment and concentration reduction, but traditional membrane for membrane distillation. For example, PVDF (polyvinylidene fluoride), PTFE (tetrafluoroethylene) and PP) all have some problems, such as low membrane flux, poor hydrophobic effect, easy clogging of membrane pore and easy wetting of membrane surface. Therefore, a kind of membrane for membrane distillation with high flux, good hydrophobicity, high salt rejection and stable operation plays an extremely important role in promoting the industrialization of membrane distillation. In this paper, superhydrophobic polyimide nanofiber membrane was prepared by using double bionic superhydrophobic modification method and electrospinning technology to prepare superhydrophobic polyimide nanofiber membrane for membrane distillation, and was applied to direct contact membrane distillation (DCMD) experiment. The effectiveness of membrane distillation under different experimental conditions was studied, and the potential application of modified polyimide (Pi) fiber membrane was analyzed. The micropore structure and hydrophobicity of membrane for membrane distillation determine the membrane flux and salt rejection. At present, the traditional membrane has some defects, such as low porosity and winding pore channel, so it is considered to use electrostatic spinning technology to prepare fiber with small diameter. In addition, the hydrophobic modification of the base membrane is one of the effective measures to delay the membrane wetting in the distillation process. At present, the methods of obtaining the hydrophobic membrane structure are in situ method and post-treatment method. In this paper, a post-treatment was carried out on the base film. Firstly, the dopamine (DA) and polyimide (PEI) could be crosslinked in water. A charged layer of biofilm, C-PDA-p-PEI, was formed, and a positively charged viscous layer was constructed without destroying the surface of the Pi fiber film, and then the negatively charged silica nanoparticles, Sio _ 2, NPs) were assembled on the surface of the nanofibers by electrostatic adsorption. The surface structure of the membrane was reconstructed, and the roughness of the fiber surface was increased. Finally, the surface energy of the fiber membrane was reduced by fluorination, and the superhydrophobic polyimide porous fiber membrane was formed on the surface of lotus leaf. The modified Pi membrane was tested by membrane distillation and compared with the Pi membrane and the PTFE membrane with different pore sizes. It can be seen that the modified Pi membrane not only occupies the advantage in stability. Moreover, the membrane flux and salt retention rate are also higher than those of PTFE membrane with the same pore size; in order to test the anti-fouling performance of the membrane, The modified Pi membrane was used to treat NaCl brine containing surfactant, humic acid, methyl blue dyes as organic pollutants, respectively. The flux and conductivity of the membrane were recorded during the experiment. It was proved that the modified Pi membrane had good resistance to pollution. Then the modified Pi membrane was concentrated and reduced by reverse osmosis (RO) concentrated water. It was found that after the volume of the feed solution was concentrated to the original 1 / 4, the salt retention rate of the membrane flux could be maintained. The results show that the modified Pi membrane can guarantee a certain anti-pollution and self-cleaning performance when the feed concentration is very high. Finally, the modified Pi membrane is used to simulate seawater desalination by membrane distillation. The technical evaluation and economic analysis of membrane distillation seawater desalination process provide another possibility for membrane selection of membrane distillation process in seawater desalination.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.893

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