【作者】 李海军；

【导师】 张捍民；

【作者基本信息】 大连理工大学 ， 环境工程， 2013， 硕士

【摘要】 正渗透(FO)膜分离技术是一种模拟自然界中的渗透现象的膜分离技术,以正渗透膜两侧溶液的渗透压差为驱动力,驱动纯水从原料液(低渗透压)扩散到汲取液(高渗透压)。正渗透过程无需外加压力,因此正渗透膜分离技术具有低污染、低能耗的特点。作为正渗透膜分离技术的核心,正渗透膜具有与反渗透膜类似的结构,即由活性层和多孔支撑层构成。研究人员发现,浓差极化尤其内浓差极化(internal concentration polarization,简称ICP)和膜污染限制了正渗透技术在实际研究与应用中的性能。因此,本论文针对正渗透膜分离技术在应用过程中出现的ICP和膜污染现象,以亲水性物质聚乙烯醇(polyvinyl alcohol,简称PVA)、氧化石墨烯(graphene oxide,简称GO)及常用的正渗透膜材料——间苯二胺(m-phenylenediamine,简称MPD)、均苯三甲酰氯(trimesoyl chloride,简称TMC)为制膜材料,制备无支撑层且抗污染的正渗透膜,并对其性能进行研究。首先,本文以PVA和GO为制膜材料,采用溶液浇铸法制备聚乙烯醇/氧化石墨烯膜。扫描电镜(SEM)结果表明其结构中无明显多孔支撑层结构。聚乙烯醇/氧化石墨烯膜表现出一定的正渗透性能,膜纯水通量为3.7升每平方米每小时(3.7LMH),盐反向通量为39.8克每平方米每小时(39.8gMH),但是其盐截留性能有待提升；第二,引入间苯二胺(m-phenylenediamine,简称MPD)和均苯三甲酰氯(trimesoyl chloride,简称TMC)等制膜材料,制备出无支撑正渗透膜。所制备正渗透膜水通量为3.5LMH,盐反向通量为9.8gMH,具有较好的正渗透性能；SEM和通量测试表明所制备的正渗透膜呈无支撑层的对称结构,并且以去离子水为原料液时,无支撑正渗透膜的水通量要比HTI (Hydration Technology Innovations)膜稳定,表明无支撑正渗透膜可以免受ICP的影响；无支撑正渗透膜的厚度仅为38μm,拉伸强度可达50MPa,满足正渗透过程膜强度要求,并且无支撑正渗透膜的亲水接触角在7°以内,表现出很强的亲水性；最后,在渗透膜生物反应器(OMBR)系统中运行时,无支撑正渗透膜的水通量比HTI膜更稳定,通过测定膜面上胞外聚合物(extracellular polymeric substance,简称EPS)含量发现,无支撑正渗透膜上的EPS含量远低于HTI膜上EPS含量,并且无支撑正渗透膜上的EPS通过自来水简单清洗即可去除,而且无支撑正渗透膜在清洗后的通量恢复也优于HTI膜,因此无支撑正渗透膜具有较好的抗污染性。更多还原

【Abstract】 Forward osmosis (FO) was an osmotically driven membrane process that simulated the osmosis phenomenon in nature, making use of the osmotic pressure difference across a semi-permeable membrane as driving force to drive water transport from (low osmotic pressure) side to draw solution (high osmotic pressure) side. Due to nearly no hydraulic pressure required, FO delivered many potential advantages such as less energy input and lower fouling tendency. As the most important factor in FO separation technology, FO membrane acquired the similar structure with reverse osmosis (RO) membrane which composed of an active layer and a porous support layer. Researchers found that concentration polarization (CP), especially internal concentration polarization (ICP), and membrane fouling restricted FO membrane performance in actual research and application. Taking above into account, we focused on the preparation of FO membranes in this study to overcome the effect of ICP and membrane fouling using hydrophilic substance, e.g. polyvinyl alcohol (PVA) and graphene oxide (GO), and common membrane materials in FO membranes, e.g. m-phenylenediamine (MPD) and trimesoyl chloride (TMC), by solution casting method.First of all, PVA/GO membranes were synthesized by solution casting method using PVA and GO. The SEM showed that PVA/GO membranes possessed no porous layers. The obtained results indicated that water flux of PVA/GO membranes was3.7LMH with salt reverse flux of39.8gMH, and also implied that rejection of PVA/GO membranes should be further increased.Secondly, MPD and TMC were selected as membrane materials to prepare free-standing membranes. The free-standing membranes possessed better performance with water flux and salt reverse flux of3.5LMH and9.8gMH, respectively. The results of SEM and water flux manifested that the FO membranes were synthesized with symmetric structures in which no distinct porous layer was distinguished. When tested with deionized (DI) water as feed solution (FS), the changes of water flux of free-standing membranes were more stable than HTI membranes, indicating that free-standing membranes could overcome the adverse effects of ICP on water flux. Moreover, the free-standing membranes were as thick as38μm with mechanical strength of50MPa which was qualified for strength requirements in FO process. Further the free-standing membranes exhibited substantial hydrophilic property with the contact angle as low as7degree. Finally, water flux of free-standing membranes was also more stable than HTI membranes when running in the osmotic membrane bioreactor (OMBR) system. The adsorbed extracellular polymeric substance (EPS) mass on free-standing membranes was much lower than that on HTI membranes. Additionally, the EPS on free-standing membranes could be easily eliminated by simple washing with running tap water because water flux recovery of free-standing membranes after cleaning was also higher than HTI membranes. Thus it could be deduced that anti-fouling property of free-standing membranes was much better than HTI membranes更多还原