PTFE平板膜微孔结构调控及膜蒸馏性能研究

发布时间：2018-06-24 21:52

本文选题：聚四氟乙烯 + 平板膜　；参考：《浙江理工大学》2015年硕士论文

【摘要】：膜蒸馏（MD）是膜技术与蒸馏过程有机结合的一种新型膜分离技术，其以膜两侧的蒸汽压差为传质驱动力，气体分子扩散透过膜孔，液体和难挥发性物质被阻隔在料液测从而实现分离目的。MD具备分离纯度高、运行条件温和等优点。然而，其产水通量低、MD膜材料抗污性差等缺点限制其应用。聚四氟乙烯（PTFE）平板膜具有强疏水、物化性能稳定、抗污性强、孔径小、孔隙丰富等优点，是MD膜的理想材料。鉴于此，本文采用“挤出-拉伸-热定型”方法制备PTFE平板膜，并将其用于气扫式膜蒸馏（SGMD）进行脱盐实验，研究平板膜制备参数对膜结构、膜性能及SGMD脱盐性能的影响，设计正交试验，优化SGMD过程中的操作参数。通过连续性实验研究膜污染及通量恢复性能。结果表明：（1）“挤出-拉伸-热定型”方法可制备PTFE平板膜，其具有独特的“原纤-结点”网状微孔结构。在制备过程中，纵向拉伸倍数增加，PTFE原纤伸长，平均孔径、孔隙率增大；横向拉伸倍数增加，节点发生劈裂，原纤倾斜，平均孔径降低，，孔隙率增大；热定型温度升高，热定型时间延长，原纤、节点收缩熔融，孔径先增大后减小，孔隙率减小。此外，PTFE平板膜热定型后结晶减小，导致其表面能降低，疏水性增强。（2）SGMD脱盐过程中，PTFE平板膜平均孔径增加，传质效率增加，产生通量提高；料液温度升高，膜两侧蒸汽压差增大，传质驱动力增强，产水通量增大；料液流速加快，温差极化、浓度极化现象削弱，产水通量提高；料液浓度增加，水的活性下降和浓差极化引起产水通量降低。脱盐率均保持在99.9%以上。（3）SGMD连续运行200小时实验过程中，膜表面会发生污染，导致产水通量有所下降。周期性清洗恢复实验表明，试剂清洗可以缓解膜污染，恢复产水通量，实验用1M酸性清洗膜的产水通量恢复率达到95%以上。
[Abstract]:Membrane distillation (MD) is a new membrane separation technology which combines membrane technology with distillation process. The vapor pressure difference on both sides of the membrane is the driving force of mass transfer, and the gas molecules diffuse through the membrane pore. Liquid and difficult volatile substances are separated in the material liquid to achieve the purpose of separation. MD has the advantages of high purity, mild operating conditions and so on. However, its low water flux and poor fouling resistance of MD membrane materials restrict its application. Polytetrafluoroethylene (PTFE) flat membrane has the advantages of strong hydrophobicity, stable physical and chemical properties, strong anti-fouling property, small pore size and abundant porosity, etc. It is an ideal material for MD membrane. In this paper, PTFE flat membrane was prepared by extrusion, tensile and heat setting method, and was used in desalination experiment of air-swept membrane distillation (SGMD). The effects of plate preparation parameters on membrane structure, membrane properties and SGMD desalination performance were studied. Design orthogonal test to optimize the operation parameters of SGMD process. The membrane fouling and flux recovery performance were studied by continuous experiments. The results show that: (1) PTFE flat films can be prepared by "extrusion-extension-heat setting" method, which has a unique "fibrillary-node" reticular micropore structure. During the preparation process, the longitudinal tensile ratio increased, the average pore size and porosity increased, the transverse tensile ratio increased, the node split, the original fiber tilted, the average pore size decreased, the porosity increased, and the heat setting temperature increased. The heat setting time is prolonged, the original fiber, the node shrinks and melts, the pore diameter increases first and then decreases, and the porosity decreases. In addition, the crystallization of PTFE plate membrane decreases after heat setting, which leads to the decrease of surface energy and the enhancement of hydrophobicity. (2) during the desalting process of SGMD, the average pore size, mass transfer efficiency and production flux of PTFE plate membrane increase, and the temperature of feed solution increases. The vapor pressure difference on both sides of the membrane increases, the mass transfer driving force increases, the water flux increases, the flow rate of the feed increases, the temperature polarization, the concentration polarization weakens, the water flux increases, the concentration of the feed increases. The decrease of water activity and concentration polarization resulted in the decrease of water flux. The desalinization rate is above 99.9%. (3) during 200 hours of continuous operation of SGMD, the membrane surface will be polluted and the water flux will decrease. The experiment of periodic cleaning and recovery showed that reagent cleaning could reduce the membrane fouling and restore the water flux. The recovery rate of water production flux reached more than 95% when the membrane was cleaned with 1m acid.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ028.8

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