CAS OpenIR
高通量/抗结垢纳米纤维膜的制备及其膜蒸馏脱盐性能研究
苏春雷
Thesis Advisor李玉平, 曹宏斌
2020-07-01
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline环境工程
Keyword膜蒸馏,抗结垢,纳米纤维膜,中空纤维膜,膜污染
Abstract

近年来,社会和经济的发展一方面加剧了对能源和水资源的需求,另一方面也加剧了对环境的污染。膜蒸馏可以利用低品位的余热和废热对高浓盐水进行处理得到高品质淡水,在减少水体环境污染的同时,还有助于缓解水资源匮乏和能源危机。膜蒸馏技术工业化应用的还需要解决的关键问题是提高膜通量以及解决膜润湿和膜污染(尤其是针对无机盐的结垢)的问题。本研究基于静电纺丝技术,从材料创新的角度出发,制备了具有高通量,抗润湿、结垢污染的纳米纤维膜,主要研究内容和成果如下:(1)结合纳米纤维膜的高孔隙率和中空纤维的高填充密度的优点设计了一种新型的基于纳米纤维组装的中空纤维膜(N-HFM)。同时通过利用非旋转电极作为接收端,以及调控纺丝过程参数开发了可以适用于连续化和规模化制备N-HFM的新技术。通过对纺丝过程条件的系统性研究发现,要实现制备结构和形貌理想的N-HFM,需要严格调控纺丝过程正、负电压和纺丝液的大小。得益于高孔隙率,本研究制备的膜的通量远高于其他传统方法制备的中空纤维膜和平板膜。(2)针对纳米纤维膜普遍存在的纤维堆积松散,孔径分布不均匀,机械强度性能差的不足,开发了一种增强纳米纤维机械强度和调控孔径分布的快捷方法:稀溶剂焊接法。主要原理是利用聚合物非溶剂组分稀释溶剂组分使其对聚合物在室温下不可溶,而在加热后局部微溶来对纤维进行焊接和分布重排。研究了焊接液组成,焊接温度和时间对焊接效果的影响,对比了焊接前后膜的形貌,孔径分布,孔隙率,机械强度,热分解曲线,结晶度和晶型等性质的的变化,证明该方式是一种快捷的提高膜的机械强度和孔径均匀性的后处理方法。膜蒸馏测试发现经过焊接处理后的膜的通量下降不大,但是膜稳定性大大提高。(3)以水溶性的PEO作为不溶性的PTFE的载体,利用乳液静电纺丝和烧结制备了纯PTFE材质的N-HFM膜。研究得出纺丝液PEO和PTFE最优质量比为8/92。对比了不同烧结温度对膜形貌、化学性质、疏水性、孔径分布和机械强度的影响。由于高的孔隙率和通孔结构,所制备的PTFE中空纤维膜的MD通量分别为商业和文献报道的PTFE中空纤维膜通量的4.6~8.8和3.6~11.6倍。另外所制备的PTFE中空纤维膜在长时间的不同温度、料液流速和盐浓度的MD实验中也表现了非常稳定的性能,证明该膜具有较大的实际应用前景。(4)针对膜蒸馏处理高浓盐水时存在的膜结垢问题,开发了一种基于电纺丝/喷雾技术和蒸汽焊接方法(ES2)制备高通量和抗结垢污染的r-SH膜。ES2工艺通过同步层层沉积纳米纤维和微球,形成独特的纳米纤维缠绑微球结构,通过焊接后纳米纤维和微球之间形成紧密的粘结,增强了膜的强度和疏水稳健性。盐水浓缩实验显示r-SH超疏水膜相对于疏水膜具有显著的缓解无机盐结垢污染的能力。基于超疏水膜面被束缚的气层提出了具有Cassie-Baxter状态(低滚动角)的超疏水膜用于缓解膜结构的三种作用机理:减少液-固接触面积,提高膜面形成异相结晶的难度,减少溶液中矿物离子和膜面相互作用时间。(5)针对疏水膜在处理含有低表面能物质的高浓盐水时同时存在的膜润湿和膜结垢问题,通过在具有再凹陷结构的纳米纤膜基膜上真空过滤涂覆氟化聚倍半硅氧烷(F-POSS)和聚二甲基硅氧烷(PDMS)混合溶液的方法制得一种同时具备低滚动角和全疏性表面的膜。该膜在膜蒸馏处理含有低表面能物质的高浓盐水过程中展现了温度的抗润湿和抗结垢性能。;In recent years, the development of social and economic not only have intensified the demands for energy and water resources, but also have intensified the environmental pollution. Membrane distillation can use low-grade residual heat and waste heat to treat highly concentrated brine and obtain high-quality fresh water, which can not only reduce environmental pollution, but also help to alleviate the shortage of water and energy resources crisis. The key problems to be solved in the industrial application of membrane distillation are to improve the membrane flux and to solve the membrane wetting and membrane fouling (especially the scaling). Based on electrospinning technology and from the perspective of material innovation, this study prepared nano-fibrous membrane with high flux, resistance to wetting and scaling pollution. The main research contents and achievements are as follows:(1) A novel nanofibers-based hollow fiber membrane (N-HFM) designed by combining the advantages of high porosity of nanofiber membrane and high filling density of hollow fiber membrane. A new technique for continuous and large-scale preparation of N-HFM was developed by using a non-rotating electrode as the collector. Through the systematic study of spinning process conditions, it is found that the the positive and negative voltage and the feed rate of electropinning solution are important parameters to prepare N-HFM with ideal structure morphology. Due to the high porosity, the flux of the membrane prepared in this study is much higher than that of hollow fiber membrane and plate membrane prepared by other traditional methods.(2) In order to solve the problems of loose stacking of nanofibes, uneven pore size distribution and poor mechanical strength, a fast method was developed to enhance the mechanical strength and control pore size distribution of nanofibers: dilute solvent welding. The main principle of this method is to dilute the solvent of a certain polymer by using the non-solvent component to make the solvent component insoluble at room temperature. Effects of the composition of welding solution, welding temperature and welding time were investigated by comparing morphology, pore size distribution, porosity, mechanical strength, thermal decomposition curve and crystallinity of membranes before and after the welding. It was proved that the dilute solvent welding is a quick method to increase membrane mechanical strength and pore size distribution. It was found that the flux of the welded membrane decreased little, but the stability of the membrane was improved greatly.(3) N-HFM membrane of pure PTFE was prepared via emulsion electrospinning and sintering using water-soluble polyethylene oxide (PEO) as the carrier of insoluble PTFE. The optimal mass ratio between PEO and PTFE was 8/92. The effects of different sintering temperatures on the morphology, chemical properties, hydrophobicity, pore size distribution and mechanical strength of the films were investigated. Due to the high porosity and through-hole structure, the MD fluxes of the prepared PTFE hollow fiber membrane were 4.6~8.8 and 3.6~11.6 times of the commercial and reported PTFE hollow fiber membrane fluxes, respectively. In addition, the prepared PTFE hollow fiber membrane also showed very stable performance in MD experiments with different temperature, material and liquid flow rate and salt concentration over a long period of time, which proved that the membrane has a great practical application prospect.(4)Aiming at the problem of membrane scaling in the treatment of highly concentrated brine by membrane distillation, a high-flux and anti-scaling r-sh membrane was prepared based on electrospinning/spray technology and vapor welding method (ES2). With the simultaneous and layer-by-layer layer deposition of nanofibers and microspheres, a unique nanofibers-binded-microspheres structure was formed. After welding the nanofibers and microspheres were welded together to enhance the membrane strength and the robustness of hydrophobicity. The results of brine concentration experiments show that r-sh superhydrophobic film has a significant ability to alleviate the scale pollution caused by inorganic salts compared with the hydrophobic film. Based on the bounded gas layer on the superhydrophobic membrane surface, three action mechanisms of the superhydrophobic film with cassie-baxter state (low sliding angle) were proposed: reducing the liquid-solid contact area, improving the difficulty of forming heterogeneous crystals on the film surface, and reducing the interaction time between mineral ions and the film surface in solution.(5) To solve the problems of membrane wetting and membrane fouling in the treatment of high concentrated brine containing low-surface-energy contaminants with the hydrophobic membrane, a membrane with low sliding angle and omniphobic surface was fabricated via vacuum-coating wtih the mixture of poly siloxane fluoride (F - POSS) and polydimethylsiloxane (PDMS) based on the re-reentrant structure of nanofibrous membranes. The fabricated membrane exhibited the anti-wetting and anti-scaling properties of in treating of highly concentrated brine coating low-surface-energy contaminants via MD process.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49697
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
苏春雷. 高通量/抗结垢纳米纤维膜的制备及其膜蒸馏脱盐性能研究[D]. 中国科学院大学,2020.
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