通过调节界面聚合反应制备正渗透复合薄膜

Fabrication of Thin Film Composite Membranes for Forward Osmosis Via Tuned Interfacial Polarization

刘格

11749132

硕士

环境科学与工程

邓保林

2019-05-28

2019-07-14

哈尔滨工业大学

深圳

作为一种新兴的膜处理技术，近年来正渗透技术受到了广泛的关注，高效正渗透膜的制备也因此成为热点。目前，较为常用的正渗透膜为复合薄膜，复合薄膜通常由一个多孔支撑底膜与一个致密分离层组成。为了减轻正渗透过程中内部浓差极化对膜分离性能所造成的不利影响，对正渗透复合薄膜的研究，重点通常放在对其底膜的调节上。正渗透复合薄膜通常倾向于选择较为亲水的底膜，但底膜亲疏水的改变会极大影响表面聚酰胺分离层的合成。因而，本研究着眼于底膜亲疏水性对复合薄膜制备的影响，通过碱处理水解对原始聚丙烯腈底膜进行亲水改性，并设置热处理控制实验，之后分别以原始、热处理、碱处理聚丙烯腈为底膜，利用原位界面聚合法制备复合薄膜，通过对比所制备复合薄膜的性能及形貌，探究了底膜亲疏水性对于聚酰胺层制备的影响。实验结果发现，经碱处理后的亲水性底膜在复合薄膜制备过程中会出现聚酰胺层脱落的状况，从而无法制备得到复合薄膜；原始及热处理两种较为疏水的底膜可成功制备复合薄膜。总结其机理得，亲水性底膜无法与聚酰胺层结合的原因是由于在制备过程中，其表面存在极薄的水层影响了聚酰胺薄层与底膜的结合。基于上述发现，本研究利用聚乙烯亚胺，聚二烯丙基二甲基氯化铵，聚丙烯胺盐酸盐三种聚电解质对经碱处理的亲水性聚丙烯腈底膜的表面进行亲疏水改性，并在改性底膜的表面进行原位界面聚合，制备复合薄膜，探究了聚电解质中间层对于界面聚合反应的调节作用。实验结果发现，经聚电解质改性的底膜亲水性总体有所降低，因而在复合薄膜制备过程中并未出现聚酰胺层剥落的现象。具体来讲，经聚乙烯亚胺、聚丙烯胺盐酸盐改性的复合薄膜水通量分别为1.32LMH，1.82LMH，20mmol/L NaCl 溶液截盐率分别为87.96%，68.94%，较原始聚丙烯腈制备的复合薄膜（水通量为1.24LMH，截盐率为61.17%）性能有所提高；经聚二烯丙基二甲基氯化铵改性而制备的复合薄膜聚酰胺层出现局部剥落的现象，不具备实际应用价值。总结可知，聚电解质层可有效调节底膜表面的亲疏水性，并影响界面聚合反应物间苯二胺的扩散，导致所生成的聚酰胺层形貌有所变化，从而影响了所制备的复合薄膜的整体性能。之后，本研究采用正渗透过程测试经聚丙烯胺盐酸盐改性的复合薄膜性能，并将其与原始聚丙烯腈底膜所制备的复合薄膜性能相对比。实验结果表明在2mol/L的氯化钠溶液作为汲取液、纯水作为进料液、选择层朝向汲取液的情况下，改性后的复合薄膜水通量提升45%左右，选择性略有提高，正渗透处理效率提升约40%。

As an emerging membrane technology, forward osmosis (FO) has attracted a lot of attention in recent years, which leads to a bloom of studies focusing on the fabrication of high-performance FO membranes. The thin film composite (TFC) membrane which consists of a porous support layer and an active rejection layer is a competitive FO membrane configuration. In order to mitigate the adverse effects caused by internal concentration polarization (ICP) in FO process, most of prior research work concentrated on the fabrication of high performance TFC FO membranes and highlighted the tuning of support layer to mitigate ICP.It is believed that the hydrophilic substrate may benefit the membrane performance in FO process, however, it may significantly affect the formation of polyamide rejection layer. This study investigated the influence of substrate hydrophilicity on the formation of polyamide layer by fabricating TFC membrane from a relatively hydrophobic pristine polyacrylonitrile (PAN) and a super hydrophilic hydrolyzed PAN substrate with TFC membranes fabricated from PAN after heating treatment as control. It was found that the polyamide layer would delaminate from the hydrophilic support, leading to the failure of TFC membrane fabrication. It was hypothesized that the delamination was probably due to the existence of a very thin water layer located between the hydrophilic substrate and the PA layer during the fabrication process.Three kinds of polycations (PAH, PEI, PDADMAC) were used to tune the surface hydrophilicity of the hydrolyzed PAN substrate and then the modified substrates were used to fabricate TFC membrane. The effects of polyelectrolytes interlayer on the substrate and PA layer were investigated by comparing the morphology and performance of the TFC membranes fabricated. According to the results, after the polyelectrolytes modification, the surfaces of the substrates became more hydrophobic and no delamination was observed during the interfacial polymerization. The water permeability of PAH modified TFC membrane and PEI modified TFC membrane were 1.32 LMH, 1.82 LMH respectively and the rejection of 20 mmol/L NaCl solution were 87.96% and 68.94%, which had an obvious improvement compared to the TFC membrane synthesized on a pristine PAN (1.24 LMH in water permeability and 61.17% in rejection). The PDADMAC modified TFC membrane whose substrate was relatively hydrophilic had a PA layer with low rejection. Based on the results of membrane characterization, polyelectrolytes had effectively tuned the hydrophilicity of the substrate which affected the diffusion of m-Phenylenediamine (MPD) solution and resulted in the change of PA layer morphology and membrane performance.The PAH modified TFC membrane and the TFC membrane fabricated on a pristine PAN were evaluated in FO process with an active layer facing draw solution (AL-DS) orientation using 2mol/L NaCl solution as draw solution and pure water as feed solution. The water flux of the modified TFC membrane increased about 45% the efficiency raised about 40% and the selectivity slightly increased compared to the TFC membrane synthesized on a pristine PAN substrate.

正渗透复合薄膜 亲水性底膜 底膜改性 界面聚合反应

TFC membrane for forward osmosis hydrophilic support substrate modification interfacial polymerization

中文

联合培养

南方科技大学

刘格. 通过调节界面聚合反应制备正渗透复合薄膜[D]. 深圳. 哈尔滨工业大学,2019.