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聚丙烯酸钠正渗透汲取液的研究及高性能正渗透膜的制备
Alternative TitleStudy on Sodium Polyacrylate as Draw Solution for Forward Osmosis and High Performance FO Membrane Fabrication
杨晶
Subtype工程硕士
Thesis Advisor张懿 ; 李玉平 ; 曹宏斌
2014-05
Degree Grantor中国科学院研究生院
Degree Discipline环境工程
Keyword正渗透   聚丙烯酸钠   聚丙烯腈   静电纺丝   中空纤维
Abstract正渗透是一种新型膜分离技术,其驱动力来源于原料液和汲取液之间本身就存在的渗透压差,相比于传统的膜分离技术,如:反渗透、纳滤等,具有产水率高、膜污染可逆和能耗低等优点,具有广阔的应用前景,近年来逐步受到研究者的关注。正渗透有两个关键问题,高渗透压且易再生的汲取液和高性能正渗透膜。本论文以聚丙烯酸钠溶液为汲取液,研究了其正渗透性能和再生性能,并制备了两种高性能的正渗透膜,主要研究内容和结果如下: 一、研究了聚丙烯酸钠溶液作为汲取液的渗透压特性,重点考察了水通量和溶质反向渗透量的影响因素及机制,探讨了聚丙烯酸钠汲取液的正渗透性能。结果表明,聚丙烯酸钠浓度和渗透压的关系符合维里方程关系,第二维里系数对渗透压有较大贡献,浓度为0.2 g/mL的渗透压达到了1.3 Osmol/kg以上。0.2 g/mL聚丙烯酸钠汲取液的水通量为14.5 L/(m2?h),略高于相同渗透压的氯化钠溶液的水通量14.1 L/(m2?h);聚丙烯酸钠汲取液的反向溶质渗透率为1.6 g/(m2?h),低于常规氯化钠汲取液的16.5 g/(m2?h);升温能迅速提高水通量,溶质反向渗透量能维持较低水平,聚丙烯酸钠汲取液适合比常规小分子汲取液更高的操作温度。聚丙烯酸钠汲取液较高的水通量和较低的反向溶质渗透率表明正渗透性能良好。截留分子量200~300的纳滤膜能实现聚丙烯酸钠溶液的浓缩再生,截留率为93%以上。 二、利用静电纺丝技术制备了高孔隙率和低弯曲度的碳纳米管/聚丙烯腈基底,在基底表面以间苯二胺水溶液和均苯三甲酰氯/正己烷溶液界面聚合形成聚酰胺薄膜,表征了复合膜的形貌结构和力学性能,测定了膜的正渗透性能。结果表明,添加碳纳米管后,膜的机械性能明显提高,碳纳米管/聚丙烯腈基膜的抗拉强度达59.38 MPa,高出聚丙烯腈基底抗拉强度1倍以上。碳纳米管/聚丙烯腈基聚酰胺复合膜亲水性好(接触角为36.6o),正渗透水通量高达147.2 L/(m2?h),反向盐通量仅42.5 g/(m2?h),正渗透性能远优于目前报道的正渗透复合膜(水通量10~50 L/(m2?h),反向盐通量10~125 g/(m2?h))。复合膜的纯水渗透系数为13.77 L/(m2?h?atm),远高于常规聚酰胺复合膜,结构参数仅为54.4 μm,优于常规聚酰胺复合膜和商业CTA膜,显示较好的膜结构性能。 三、利用静电纺丝机制备了有序超细中空纤维膜,研究了制备条件对纤维形貌、平均直径、中空结构、有序度及力学性能的影响,以期将最佳条件下制备的纤维膜用于正渗透脱盐。结果表明,当纺丝电压为15 KV,接收距离为14 cm,外液流速为0.8 mL/h时,能制备出表面形貌较好,机械性能较强的连续纤维;外液流速为0.8 mL/h时,能制备出中空结构较好的纤维;采用滚轴式接收装置收集纤维,随滚轴转速的提高,纤维有序度有一定的提高。超细中空纤维比表面积大,使得装填密度高于传统中空纤维膜,相同体积的膜组件可产生更高的水通量。
Other AbstractForward osmosis (FO) is a novel membrane separation technology using the osmotic pressure difference naturally existed between draw solution and feed solution as the driving force. FO takes advantages of high water production rate, reversible membrane fouling and low energy consumption over traditional membrane technologies such as reverse osmosis, nanofiltration, and possesses broad prospects and gains increasing attentions recently as a result. There are two key challenges for FO: (1) draw solution of high osmotic pressure and easy recovery, (2) high performance membrane. In this work, we developed a FO system using sodium polyacrylate as the draw solution, and synthesized two types of high performance FO membranes; details were as follows: 1. Osmosis property of sodium polyacrylate (PAA-Na) as draw solution was investigated, and the forward osmosis performance using this draw solution was discussed with focus on influence factors and effective mechanism for water flux and reverse solute flux. The results show that the fitting curve of osmotic pressure and PAA-Na concentration matches “Virial Equation”, and the second Virial coefficient promotes the osmotic pressure dramatically at a certain concentration range; the osmotic pressure of 0.2 g/mL PAA-Na is over 1.3 Osmol/kg, showing the great advantage of PAA-Na as draw solution. The permeate flux in the forward osmosis process with 0.2 g/mL PAA-Na as draw solution reaches 14.5 L/(m2?h), which is slightly higher than that of NaCl draw solution with the same osmotic pressure [14.1 L/(m2?h)]. The reverse solute flux with 0.2 g/mL PAA-Na as the draw solution is only 1.6 g/(m2?h), which is much lower than the case using NaCl as the draw solution [16.5 g/(m2?h)]. The water flux increases significantly with the increase of temperature while the reverse solute flux remains at a low level, indicating that the suitable operation temperature with PAA-Na as the draw solution should be higher than that with conventional small molecule as the draw solution. The results indicate that PAA-Na is a good potential draw solution due to its great water flux as well as its low reverse solute flux. PAA-Na can be well concentrated by using nanofiltration with molecular weight cutoff of 200~300, and the retention rate is over 93%. 2. Novel thin film composite (TFC) membrane with carbon nanotubes (CNTs)/polyacrylonitrile hybrid nanofibers as the membrane support was developed. The hybrid nanofibrous support with high porosity and low tortuosity was fabricated via electrospinning of uniformly mixed oxidized CNTs and PAN solution, and the developed TFC membrane was fabricated by using interfacial polymerization of polyamide on top of the support. The morphology, structure and mechanical properties of TFC membrane were characterized and the membrane’s forward osmosis performance was evaluated. The results show that the mechanical properties are significantly improved with addition of MWCNTs, and the tensile strength of MWCNTs/PAN nanofibrous support reaches 59.38 MPa, which is twice higher than that of pure PAN nanofibrous support (27.84 MPa). The developed FO membrane with PAN-nanofiber as the support exhibits hydrophilic characteristics (contact angle 36.6°), and a high FO performance with water flux of 147.2 L/(m2?h) and reverse salt flux of only 42.5 g/(m2?h), which is much better than literature reported TFC-FO membranes with a typical water flux of 10~50 L/(m2?h) and a reverse salt flux of 10~125 g/(m2?h). The developed membrane also has a higher pure water permeability of 13.77 L/(m2?h?atm) and a better structure (structural parameter is 54.4 μm) than traditional TFC membranes and commercial CTA membranes. 3. Aligned fine hollow nanofibers were fabricated via electrospinning, and the effects of technological parameters on morphology, mean diameter, hollow structure, arrangement and mechanical properties were studied. The well fabricated hollow nanofiber membrane is expected to apply in forward osmosis desalination. The results show that the aligned fine hollow fibers with uniform diameter and good mechanical properties can be prepared at the optimum conditions as follows, electrospinning voltage of 15 KV, collecting distance of 14 cm, shell flow rate of 0.8 mL/h. The wire drum collector with high rotation speed makes the hollow fibers highly aligned. The fine hollow fibers may have higher packing density over conventional hollow fibers due to its larger specific surface area and smaller fiber diameter, suggesting larger water flux in forward osmosis at the same module volume.
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15572
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
杨晶. 聚丙烯酸钠正渗透汲取液的研究及高性能正渗透膜的制备[D]. 中国科学院研究生院,2014.
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