【作者】 徐丽；

【导师】 徐又一；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2007， 硕士

【摘要】 膜蒸馏是一种新型的膜分离过程，在海水与苦咸水淡化、超纯水的制备、化学物质的浓缩和回收等领域有着广泛的应用前景。近年来，膜蒸馏对所用膜材料的要求越来越高，不仅要具有较强的稳定性、耐氧化性、耐腐蚀性和疏水性，而且还必须具有较高的气通量。针对此问题，本论文以PVDF和PES两种膜材料为研究对象，研究了膜蒸馏用疏水分离膜的制备和改性方法，其主要内容有：相转化法制备PVDF均质微孔膜的结构控制、PVDF复合膜的制备及真空膜蒸馏工艺的研究、PES微孔膜的疏水改性及其在膜蒸馏中的应用。采用光透射动力学实验研究了PVDF相转化成膜的动力学过程，并采用扫描电镜、压汞仪、接触角仪等对膜结构和性能进行表征，考察了主要成膜参数（聚合物溶液浓度、添加剂使用和浓度、凝固浴组成和温度）对膜结构与膜蒸馏性能的影响。研究结果表明：随着聚合物浓度、添加剂CaCl₂含量和凝固浴中溶剂DMAc含量的增加，PVDF成膜体系更倾向于发生延迟分相，所形成膜的表面更为致密，亚层由指状孔结构过渡为海绵状结构；当铸膜液中非溶剂H₂O的含量和凝固浴温度增加时，体系发生瞬时液—液分相的速率加快，形成亚层为指状大孔的多孔膜；当铸膜液中PVDF浓度为10.0wt.％、CaCl₂为3.0wt.％、H₂O为2.0wt.％时，以室温下的纯水为凝固浴的条件下所制得膜的孔隙率达85.14％，气通量达0.50 cm³／cm²·s·cmHg。以聚酯无纺布为支撑材料，采用含非溶剂H₂O分别为0、1.0wt.％和2.0wt.％的铸膜液制备平板复合膜，并将其用于真空膜蒸馏过程，考察料液流速、进料温度、料液浓度以及真空度对膜蒸馏通量和脱盐率的影响。结果表明：料液温度或真空度增大，蒸馏通量增加，在进料温度为65℃的条件下，蒸馏通量可达到5.39L／m²·h；随着料液浓度的增大，膜蒸馏通量轻微下降；当进料流速增大时，温度极化减弱，而蒸馏通量增大，但增大幅度逐渐变缓。以全氟正己烷为等离子体源对PES微孔膜进行表面疏水改性，X光电子能谱（XPS）分析结果证实了全氟正己烷在膜表面的存在，膜表面氟含量最高达到49.3％。改性后的膜疏水性显著提高，水接触角从92.0°提高到123.0°。采用扫描电镜观察发现改性膜的表面被一薄层覆盖，但膜的本体结构无明显变化。将改性后的膜用于真空膜蒸馏淡化模拟海水的试验中，结果表明在进料温度为60℃的情况下，改性膜的脱盐率达99.99％，通量达4.53L／m²·h。更多还原

【Abstract】 As a novel and high efficiency process, membrane distillation （MD） is often employed in desalination of sea water, preparation of superpure water, concentration and recovery of chemicals, and so on. In recent years, the development of MD technique requires a higher performance for the membrane materials. First and foremost, the membrane for MD should be highly hydropbobic. Moreover, these materials should possess excellent chemical resistance, high gas permeability, good physical and thermal stability. In this work, poly（vinylidence fluoride） （PVDF） and polyethersulfone （PES） were used to prepare hydrophobic membranes for MD process. The preparation and modification of MD membranes were investigated. The main work are divided into three aspects: the structure control of PVDF membranes prepared by immersion precipitation method, the preparation and MD properties of PVDF composite membranes, the hydrophobic modification and MD properties of PES porous membrane.The dynamic process of PVDF membrane-forming system was studied via light transmission experiments. The structure and performances of the obtained PVDF membranes were characterized using scanning electronic microscope （SEM）, mercury porometer, contact angle instrument etc. The influences of the main factors including polymer concentration, additive concentration, coagulant composition and casting temperature on membrane structure and properties were investigated. It was found that, with the increase of polymer concentration, CaCl₂ concentration in casting solution and DMAc concentration in coagulation bath, the system tended to delayed de-mixing. The resultant membranes had a dense skin layer and a sponge-like sub-layer. When added amount of H₂O in the casting solution and casting temperature ascended, the system tended to instantaneous de-mixing and the obtained membranes had a porous skin and finger-like sub-layer. When PVDF concentration in the casting solution was 10 wt.%, CaCl₂ concentration was 3 wt.%, H₂O concentration was 2 wt.%, and the room temperature water was used as the coagulation, the porosity of the obtained membrane was 85.14 % and the nitrogen gas flux was 0.5 cm³/cm²·s·cmHg.The PVDF composite membranes were prepared and used in vacuum membrane distillation（VMD） for desalination, the effects of feed temperature, feed concentration, flow rate and vacuum pressure on distillation flux and dealination rate of membranes were investigated. It was found that the distillation flux went up with the feed temperature and pressure difference. The distillation flux of the membrane reached 5.39 L/m²·h when the feed temperature was 65℃. With the increase of feed concentration, the distillation flux slightly declined. The distillation flux increased with the flow rate, while it ascended slightly when the flow rate increased.The hydrophobic surface modification of PES microporous membranes was achieved via low temperature perfluohexane plasma treatment. X-ray photoelectronic spectroscopy （XPS） results confirmed the existence of perfluohexane segments on the membrane surfaces and the content of fluorin reached 49.3 %. Water contact angle of the membranes increased from 92.0° to 123.0°, suggesting the hydrophobicity of the membranes was improved significantly. Furthermore, SEM images showed that the surface of the modified membrane was covered by a lamella which contained fluorin, but the main structure was not changed. The modified membranes were applied in VMD for desalination. The experimental results showed that, under a low Re constant, the desalination ratio was 99.99 % and the distillation flux reached 4.53 L/m²h.更多还原