【作者】 杨兰；

【导师】 马润宇；

【作者基本信息】 北京化工大学 ， 化学工程， 2001， 硕士

【摘要】 膜蒸馏是一新型的膜分离技术。它利用高分子膜的微孔性、疏水性来实现水的纯化及溶液的浓缩等目的。膜蒸馏技术具有省能、高效、操作简单等优点。但目前还存在一些尚待解决的问题影响着它的工业应用。制得质优价廉的膜便是关键的问题之一。 本文通过一定的实验和理论工作，对膜蒸馏用聚偏氟乙烯疏水微孔膜的制备进行了初步研究。对制膜液中聚合物及添加剂的浓度、第二添加剂及其用量以及凝胶浴的温度和组成对膜结构形态的影响进行了详细的讨论。利用电子显微镜对膜结构进行了观察。实验结果显示出，以15％的聚偏氟乙烯(PVDF)为原料、75％的N，N二甲基乙酰胺(DMAC)为溶剂、3％的氯化锂(LiCL)和7％的聚乙二醇(PEG)为添加剂的制膜液，所制得的膜具有较大的孔隙率和孔径。通过对以醇／水溶液为凝胶浴以及用相转化湿法制备聚偏氟乙烯疏水微孔膜的影响因素的分析，最终选定凝胶浴条件为30℃左右的水。这是因为以水作凝胶剂不但凝胶速度最大，同时还适合于大规模工业生产应用。另外，将制膜液与无纺布恰当匹配，可改善膜面的效果，增强膜性能，并减少膜缺陷的产生。 本文用直接接触式膜蒸馏和气隙式膜蒸馏对不同材料的膜进行了渗透性能评价及渗透性能影响因素的研究。实验结果表明，在相同的操作条件下，可将膜的渗透性能参数和温度极化系数这两者综合考虑，作为膜渗透性能评价的依据。另外膜的渗透性能参数及温度极化系数还受操作条件等因素的影响，因此控制好适宜的操作温度、流体流率以及料液中溶质的浓度等操作条件也是非常重要的。为了防止膜被润湿以至被污染，料液在进入膜蒸馏系统前应先进行预处理。在溶液浓缩应用中，需采取适当措施来减轻因料液浓度加大导致其粘度增加而出现的膜通量衰减的现象。更多还原

【Abstract】 Membrane distillation(MD) is a relatively new membrane separation process. Essentially the process employs hydrophobic porous membrane which is permeable to vapor but not to the liquid phase to realize water purification and solution concentration. The advantages of MD are energy efficient, cost efficient and operation easy. At present, the wide commercial use of MD has not yet been achieved mainly due to the preparation of fine and cheap MD membrane.In this paper, the preparation of hydrophobic microporous polyvinylidene fluorid (PVDF) membrane for MD has been studied theoretically and experimentally. The effects of the concentrations of PVDF and addictive in the casting solution, the second addictive and its content, the composition and temperature of the coagulation bath on the morphology of the membrane were discussed in detail. The morphology of the membrane was examined by scanning electron microscope. The result showed that the casting solution composed of 15%PVDF, 75%N,N-dimethyl acetamide, 3%lithium chloride and 7%polyethylene glycol could perform the membrane with high porosity and pore size. Through analyzing the factors that affects gelatin rate and membrane structure of PVDF formed through phase inversion using aqueous alcohol solution as the gelatin medium, the 30℃ water was chosen to be the gelatin medium because of its fastest gelatin rate and being suitable to the large scale industrial production. In addition, the matching of membrane casting solution with non-woven cloth could improve the final membraneproperties and avoid the membrane detects.In this paper, the permeability of several kinds of microporous membrane, which were made of different materials, have also been testing by direct contact MD and air-gap MD. It was found by the experiment that the evaluation of membrane’s permeability could base on the function of both the permeability coefficient and the temperature coefficient. Furthermore, the operation condition has great affection on the membrane’s permeability. It is important to control the temperature, flow rate and the concentration of the solution. The analysis implied that the membrane fouling and wetting control could be achieved through the prefiltration of feed and measure should be taken to reduce the flux decay resulted from the viscosity increase during the concentration of solution.更多还原