聚醚砜膜蒸馏膜制备及真空旋转膜蒸馏海水淡化过程研究
文献类型：学位论文
| 作者 | 闫会 |
| 学位类别 | 硕士 |
| 答辩日期 | 2012-06-04 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 万印华 ; 沈飞 |
| 关键词 | 聚醚砜 膜蒸馏 非溶剂致相转化 干化处理 旋转膜组件 海水淡化 |
| 其他题名 | Preparation of polyethersulfone membranes for membrane distillation and seawater desalination by a vacuum rotating membrane distillation |
| 学位专业 | 化学工程 |
| 中文摘要 | 膜蒸馏是一种热驱动型新型膜分离过程。它以疏水多孔膜为分离介质，在膜孔不被润湿的前提下，被处理料液中挥发性组分在膜两侧蒸汽压差的驱动下以蒸汽形式透过膜孔，因而该过程对非挥发性组分具有理论上100 %的截留率。因此，膜蒸馏技术在海水及苦咸水淡化、化工料液浓缩等领域具有广阔的应用潜力。但发展至今，膜蒸馏技术仍未实现工业化应用，膜及膜组件性能不佳和膜材料可选范围有限是其中的主要原因。针对上述问题，本论文主要开展了以下三方面的研究工作： (1)研究了两种不同的干化方式对所制PES膜结构及膜蒸馏性能的影响，包括自然干化和醇类液体置换干化；并采用原子力显微镜(AFM)和扫描电子显微镜(SEM)表征了PES膜的结构形貌，测定比较了其接触角、孔隙率、气体渗透性、水穿透压力(LEPw)及真空膜蒸馏(VMD)性能。结果表明，所制PES膜呈不对称双层结构，包括一定厚度的多孔海绵状皮层和指状大孔亚层，其中指状大孔贯穿于膜底部；经过干化处理，可将NIPS法制备的湿态PES膜转成可用于膜蒸馏过程的干态PES膜，该干态PES膜具有一定的LEPw值(＞0.15MPa)和较高的孔隙率(90%左右)，常压下不被所处理的料液润湿，VMD运行测试中没有发生液体穿透现象，符合膜蒸馏膜的基本特征；不同的干化方式对PES膜断面结构影响较小，但对膜表面及皮层结构有较大影响，其中以异丙醇置换干化的效果相对最佳。本论文制备的PES膜展现出了优异的膜蒸馏性能，处理70 ℃下3.5 wt.%的NaCl水溶液时，VMD通量和脱盐率分别可达74.2 kg/m2?h和99.99 %；在70 h的VMD连续脱盐过程中，所制PES膜的性能也始终保持稳定；处理80 ℃下5 g/L的乳糖溶液时，VMD通量可达111.7 kg/m2?h，脱糖率接近100 %，表明具有良好的膜蒸馏研究价值与应用前景。 (2)针对铸膜液组成对PES膜结构和VMD脱盐性能的影响进行了研究，重点考察了PES浓度、添加剂种类和浓度以及溶剂种类的影响。结果表明，相比于其他结构的膜，当PES膜具有较高孔隙率同时膜表面呈细小纳米级微孔结构而膜断面为双层结构时，能够提供更高的VMD性能，而通过铸膜液组成的合理配置，能够调控其结构尤其是断面结构中多孔海绵层厚度和指状大孔形貌。 (3)结合太阳能集热、动态旋转膜分离与膜蒸馏海水淡化三者的优点开发了太阳能真空旋转膜蒸馏集成技术并兼顾了系统的热量回收。设计加工了一套装填膜有效面积0.28 m2的太阳能真空旋转膜蒸馏海水淡化装备系统，现场考察了海水温度、膜板转速和膜下游侧真空度对系统性能的影响，同时还对真空旋转膜蒸馏过程中膜面边界层内的传热与传质进行了研究。结果表明，本文研制的真空旋转膜蒸馏海水淡化装置能够提供高达0.90～0.98的温差极化系数(TPC)和33 kg/m2?h的淡水通量(80 ℃、450 r/min、真空度95 kPa)，且计算通量与实测结果较为一致，为膜蒸馏过程提供了一种新的技术选择。计算与实测结果也同时表明，在高海水温度和高膜转速的情况下该装置运行过程将受膜面传质控制，这为下一步优化装置结构和高性能膜品种的选择提供了研究基础。 |
| 英文摘要 | Membrane distillation (MD) is a thermally driven membrane separation process where a non-wetted hydrophobic porous membrane acts as a separation medium. In MD process, volatile components in feed transport through membrane pores driven by a vapor partial pressure difference across the membrane used, while, nonvolatile components are theoretically 100% rejected. Therefore, MD technique possesses the capability of broad application potential in seawater and brackish water desalination, concentration of solutions in chemical industries. But up to now, a commercial application of MD technique is still not realized, mainly due to its poor membrane or membrane module performance, and the limited option of membrane material for MD process. For trying to overcome the above problems, in this thesis, the following two research works have been carried out: (1) preparation and characterization of polyethersulfone (PES) membranes for MD process, (2) development of a novel intergrated MD technique and its equipment for seawater desalination, named as solar-driven vacuum rotatating membrane distillationprocess. (1)The effects of a drying process on the morphology and performance of the PES membrane were then investigated at first. Two different kinds of drying processes were performed respectively, including nature drying and alchohols liquid replacement drying. After drying, the PES membranes were characterized through atomic force microscope (AFM) and scanning electron microscope (SEM) observations, contact angle (CA) measurements, porosity determinations, gas permeation rateand liquid entry pressure (LEPw) tests. The dried PES membranes were also tested in VMD process. Results showed that, an asymmetric structure with dual-layer was found in the dried PES membranes, including a porous spongy-like skin layer with a moderate thickness, and a finger-like macrovoid layer where the finger-like macrovoid penetrated the membrane cross-section. After being dried, the PES membranes have a LEPw value generally higher than 0.15 MPa, as well as a higher porosity around 90%, which attribute their potential wetting resistance over the solution treated. Subsequently, there was no liquid penetration phenomenon happened in the VMD tests of the Nacl solutions and the lactose solutions with concentrations from 3.5 wt. % to 35 wt. % and from 5 g/L to 30 g/L, respectively. All of the above characteristics indicated that, the prepared PES membranes satisfied the basic features of a membrane which can be using in MD process. Different drying processes had little influence on the membranes cross–section, but had a distinct influence on their skin layer. Among the different drying process, the best one was the liquid replacement drying where isopropanol was used. The PES membranes prepared in this thesis showed an excellent VMD performance. When a NaCl solution with concentration of 3.5 wt. % was treated at 70℃ under vacuum degree of 100 kPa, a high membrane flux of 70 kg/m2?h was achieved with a NaCl rejection of 99.99 %. In addition, the PES membrane presented a very stable desalination performance during a 70 h continuous VMD test.When a 5g/L lactose solution was treated at 80 ℃ under vacuum degree 100 kPa, a very high VMD flux up to 111.7 kg/m2?h and a lactose rejection close to 100% were obtained. The results above mentioned demonstrated that the PES membranes had a good application potential for MD process. (2)The membrane casting solution composition was also investigated, especially PES concentration, solvent nature, additive and its concentration. Besides, more attentions were paid to the different membrane structures resulting in a large difference in their membrane performances. It was found that, if membranes had similar higher porosity, compared to other structures, the membrane having a dual-layer structure in membrane cross-section with nano-scale pores in membrane surface generally showed a better VMD performace. Especially, the so-called dual-layer structure consisted of a porous spongy-like skin layer with a moderate thickness and a finger-like macrovoid layer where the finger-like macrovoid penetrated the membrane cross-section. (3)An integrated system for seawater desalination, named as solar energy driven vacuum rotating membrane distillation system (SEVRMD), was aslo developed. The SEVRMD system, taking into account the design of latent heat recovery, was expected to have the advantages attributed to the combination of solar energy collection, dynamic rotating membrane separation and membrane distillation desalination. The SEVRMD system with an effective membrane area of 0.28 m2 had been tested for the seawater desalination at the scene. The effects of feed temperature, membrane rotating speed and downstream vacuum degree on system performances were studied, as well as the heat and mass transfer within the upstream boundary layer. Results showed that, the system could provide high TPC values from 0.90 to 0.98, and a high flux of 33 kg/m2?h at seawater temperature of 80 ℃ under vacuum degree of 95 kPa. Membrane fluxes in the system were also caculated based on a series of empirial equations, and the calculated results could fit the measured values well, which provided a new technique option for seawater desalination. From the caculated and measured values, it was also found that, the mass transfer would be the dominant factor in this system at high feed temperature and high membrane rotating speed, which gave us the optimization directions of the membrane module configuration and the selection of membranes with high performance. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1792]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 闫会. 聚醚砜膜蒸馏膜制备及真空旋转膜蒸馏海水淡化过程研究[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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