【作者】 侯同刚；

【导师】 陈欢林；

【作者基本信息】 浙江大学 ， 生物化工， 2008， 博士

【摘要】 本文首先从PVA(聚乙烯醇)/PVDF(聚偏氟乙烯)复合膜的底膜PVDF入手,针对渗透汽化过程的特点对底膜结构进行改进。研究了相转化法制膜过程中各种制膜条件对膜结构的影响,包括聚合物分子量、浓度、致孔剂种类和含量、表面活性剂以及纺丝条件等方面,发现提高铸膜液的粘度可以克服弱内凝胶浴导致的纺膜不稳定的现象,但高粘度下由于铸膜液流动性差,得到的膜微观结构不均一;PEG作为添加剂含量较高时,膜截面并不是无规大孔结构,而是规则的、指状孔充分发展的单皮层膜,这种结构的形成受到溶剂与非溶剂传质速度以及皮层的形成速度影响。但所得膜的机械强度较差;溶剂对膜最终结构的影响非常大,选择易于形成大孔的NMP或DMSO等溶剂有利于得到贯穿的指状孔结构。以NMP作为溶剂的铸膜液,即使采用弱内凝胶浴,在纺制过程中仍然可以保持稳定,而NMP溶液的粘度反而低于同浓度下的DAMc溶液。可见,影响纺丝稳定性的关键并不是铸膜液的粘度,而在于皮层的形成速度,形成速度越快,纺丝越不稳定。另外,实验发现膜截面的指状孔可以在海绵状孔下部发生,这说明成膜过程中,弱内凝胶浴会扩散进入铸膜液,平板膜中膜底部常见的海绵状孔结构是由于溶剂不断溶出所造成。在上述研究的基础上,成功纺制了单外皮层、指状孔充分发展的PVDF中空纤维膜。常规的涂敷法所制的中空纤维复合膜稳定性比较差,因此本文对PVA/PVDF复合膜的稳定性进行了研究,以探明影响中空纤维复合膜稳定性的因素。初步考察了常用中空纤维式膜材料的热收缩特点以及碱处理对膜造成的影响。中空纤维膜在较高温度下通常会发生不同程度的热收缩,这是由于其制膜工艺的特殊性使得高分子链非晶区产生了一定程度取向的缘故。对平板式底膜而言,由于有无纺布支持,其长度基本不受实验条件的影响。通过中空纤维式复合膜与平板式复合膜的对比,以及分离层材料的热收缩研究发现,中空纤维式底膜的热收缩是稳定性差的重要原因,另外,实验发现过量的碱处理会对底膜的结构产生破坏。在此基础上,制得了稳定性较高的中空纤维复合膜,并研究了进料温度,进料浓度等操作条件对中空纤维式渗透汽化复合膜分离性能的影响。为改善膜的分离性能,本文尝试将无机粒子与PVA材料进行共混,制得有机-无机杂化膜。首先合成了聚丙烯酰胺/蒙脱土纳米复合物,经XRD及透射电镜表征,MMT的片层结构已经完全剥离,并分散在PAM的基体中。将PAM/MMT纳米复合物与PVA溶液共混,所得共混膜在耐溶胀性能方面得到了改善,并讨论了MMT的片层结构对共混膜渗透汽化性能的影响。其次,本文合成了疏水性微粒,制备了silicalite纳米粒子,X射线衍射表明合成的粒子为silicalite-1型,粒径约0.98um。研究了该疏水性粒子与PVA共混后,对共混膜渗透汽化性能的影响。实验发现,疏水性微粒的添加并没有减弱膜对水的选择性,相反,膜的分离因子随着微粒的添加量的增加而增大。本文最后对异丙醇水混合物在PVA膜中的传质情况进行了研究,根据溶剂扩散理论和Flory-Huggins理论,建立了333K下异丙醇水在PVA膜中的传质模型。模型计算值与实验值吻合良好。更多还原

【Abstract】 As an emerging technology, membrane technology is increasingly expanding and the number of people dealing with membranes is growing rapidly because of its intrinsic properties of energy saving and clean. Membrane technology is believed to be one of the innovative and high technologies at 21 century.Since the successful commercialization of pervaporation for ethanol dehydration launched by GFT in 1980s, the development of this process is restricted by the the low flux. Membranes and modules with high flux is desirable, and more over, lower cost is also one of the goal of this process. In order to solve the problem mentioned above, pervaporation dehydration with hollow fiber membrane and module were studied in this paper.Firstly, the fabrication of hollow fiber membrane was studied. Factors that could influence the membrane structure were investigated, including polymer molecule weight, polymer concentration, additives and surfactants etc. It was found that fabrication was unstable and nascent membrane was un-circular when using "weak coagulation". Dope solution with high viscosity can improve the stability, while the microstructure of the resulting membrane was uneven. After investigate the influence of the solvents, we found that the instability of the fabrication was caused by the fast formation of the skin layer. When PEG concentration in the dope solution is high (>8wt%), the resulting membrane has regular fingerlike structure due to the different exchange speed of the solvent and non-solvent, while the mechanical strength of such membrane is poor. The finger like structure can originate from beneath the sponge like structure, which improve that during the fabrication, the "weak coagulation"has diffused into the nascent membrane. The PVDF hollow fiber membrane single skin layer and finger like structure in the cross section was fabricated successfully, and the pervaporation performance was improved by using such membranes.The structure stability of hollow fiber composite membrane made by routine method is poor, and the factors that affected it are investigated. The main factor that leads to the breakage of composite membrane structure is thermal shrinkage of the support membrane. The thermal shrinkage of hollow fiber membrane is due to the special manufacturing process, which leads to the orinentation of the polymer chains. While flat sheet membranes have no thermal shrinkage due to the support of non-woven fabric. And more over, pretreatment of alkali will also damage the membrane structure, which should be pay more attention. Effect of temperature, feed concentration, hollow fiber module length and packing density on the composite membrane performance were studied.Inorganic nano-particals were filled to the PVA solution to improve the membrane performance. PAM/MMT nano-composite was synthesized by in situ polymerization and characterized by XRD and TEM. The effect of MMT on the hybrid membrane was investigated. The hydrophobic silicalite nano-particals were synthesized, and the influence was also discussed.Based on solution-diffusion model and Flory-Huggins theory, the transport model of isopropanol-water system in PVA membrane was established at 333 K. The calculated values of the model were in good agreement with experimental values.更多还原