【作者】 张晨；

【导师】 王志；

【作者基本信息】 天津大学 ， 化学工程， 2009， 硕士

【摘要】 水通量是反渗透膜最重要的性能参数之一。水通量越高,意味着处理同量液体的能耗越低。本文采用界面聚合法,以聚砜超滤膜为支撑层,将间苯二胺(MPD)和均苯三甲酰氯(TMC)分别作为水相和有机相单体制备了聚酰胺反渗透复合膜,并在225psi和25℃下测定了复合膜处理2000ppm NaCl水溶液时的水通量和截留率。本文主要从优化制膜工艺条件的角度研究了提高复合膜水通量的方法,并讨论了复合膜分离性能和活性分离层结构之间的关系。首先制备了水相含有不同浓度DMSO的复合膜,并使用SEM观察了复合膜的表面和断面形貌。结果表明,随着水相DMSO的浓度增加,复合膜的水通量增加,截留率降低。当水相DMSO浓度为2wt%时,复合膜同时有着较佳的水通量和截留率,分别为47.7 L.m-2.h-1和98.7%。制备了水相含有不同浓度阴离子表面活性剂十二烷基硫酸钠(SDS)的复合膜,采用SEM和AFM观察了复合膜的表面和断面形貌。结果表明,当水相中SDS浓度低于0.2wt%时,复合膜的水通量随SDS浓度的增加呈线性下降,而当SDS浓度达到0.2wt%后,复合膜的水通量趋于稳定。通过测定SDS在水相溶液中的临界胶束浓度,以及研究MPD在有机相中的扩散发现,水相中SDS胶束的形成使MPD在水相有机相界面处的浓度增加,进而使反应区内MPD浓度增加,导致活性分离层更加致密,故使复合膜水通量降低。考察了界面聚合反应时间对复合膜分离性能以及活性分离层结构的影响,发现随着反应时间的延长,复合膜的水通量先降低后趋于稳定,而截留率先升高后逐渐达到定值。结合复合膜断面的SEM图片,解释了反应时间影响活性分离层厚度和复合膜分离性能的机理。通过AFM对比了不同反应时间下复合膜表面的粗糙度,发现反应时间越短,膜表面的粗糙度越低。最后,本文对聚酰胺-聚苯胺纳米复合反渗透膜的制备进行了初步探索。经过对制膜工艺条件的优化,反渗透复合膜的水通量得到了很大的提高,复合膜综合性能最佳时的水通量和截留率分别为97.8 L.m-2.h-1和97.0%。更多还原

【Abstract】 Water flux is one of the most important performance indicators of reverse osmosis membrane. Higher water flux indicates lower energy cost when the membrane is treating the same volume of feed solution. In this paper, polyamide thin film composite (TFC) reverse osmosis (RO) membrane was prepared by interfacically polymerizing m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on top of a polysulfone substrate to form an ultrathin active layer. The separation performance of the membrane, i.e. water flux and salt rejection, were evaluated under operating pressure of 225 psi using 2000 ppm sodium chloride solution. The membrane preparation conditions were optimized to improve the water flux of the composite membrane. Relationships between membrane performance and active layer structure were also studied.Firstly, composite membranes were prepared by adding different amount of dimethyl sulfoxide (DMSO) in the polyamine solution. Surface and cross section of the top active layer were studied by SEM. Membrane testing results showed that water flux increased while salt rejection decreased with increasing DMSO concentration. Good water flux and salt rejection (47.7 L.m-2.h-1 and 98.7%) were obtained when concentration of DMSO in the polyamine solution was 2wt%.In addition, composite membranes were prepared by adding different amount of anionic surfactant sodium dodecyl sulfate (SDS) in the polyamine solution. Membrane surface structure was studied by SEM and AFM. Testing results showed that water flux decreased in a linear fashion before SDS concentration reached 0.2wt%, and leveled off afterwards. By determining critical micelle concentration (CMC) of SDS in the polyamine solution and studying diffusion of MPD in the organic phase, it was found that the formation of SDS micelles led to higher concentration of MPD in the water-hexane interface as well as the reaction zone, which resulted in formation of denser active layer and decreased water flux.Impacts of reaction time on separation performance as well as active layer structure of the composite membranes were also studied. It was found that with increasing reaction time, water flux decreased and then leveled off while salt rejection increased before staying constant. How increasing reaction time led to changes in ultrathin film thickness as well as composite membrane separation performance was explained by comparing SEM images of membrane cross sections. By studying SEM and AFM images of composite membrane surface, it was found that membrane surface become rougher with increasing reaction time.Finally, preparation of polyamide-polyaniline thin film nanocomposite reverse osmosis membrane was explored in this paper.Very high water flux as well as acceptable salt rejection (97.8 L.m-2.h-1 and 97.0%) were obtained after optimizing membrane preparation conditions described above.更多还原