超疏水纳米纤维电纺复合膜的制备及其膜蒸馏过程机理研究

Nowadays, the industrial implementation of membrane distillation (MD) is not yet feasible because of the unsatisfying hydrophobicity, weak mechanical strength and low permeate flux of the employed membrane. In this research project, a novel hydrophilic/hydrophobic composite membrane was developed to try to solve this key problem. The novel composite membrane was fabricated through the Support Enhanced - Dual Electrode Electrospinning (SE-DEES) method by dispersing hydrophobic modified nano-particles in PVDF polymer solution to prepare the hydrophobic separation function layer and using hydrophilic polyester (PET) nonwoven fabric as the supported layer. The separation function layer and supported layer were separated in the composite membrane, so the prepared membrane obtained excellent mechanical properties. The electrospun nanofibers accumulated on PET nowoven fabric were helpful to improve membrane permeate flux because there was no blind pores in the hydrophobic separation function layer. The most important was that the membrane surface was a lotus-like micro- and nano-scale structure, which ensured the membrane surface superhydrophobicity. It can be expected to prepare a hydrophilic/hydrophobic composite membrane with super surface hydrophobicity, high mechanical strength and excellent permeability through the SE-DEES method. The MD reactor was set up by using the spun composite membrane as the separation medium to treat the wastewater containing high salinity and high concentration organic compounds. In this research project, the functional properties of the composite membrane were characterized in detail, the bionic lotus-like micro- and nano-scale structure in membrane surface was comprehensive investigated and the mechanism of interface interaction between membrane surface and fluid was also explained. The process of mass and heat transfer during MD process was analyzed and a numerical model considering temperature polarization and concentration polarization was developed. This research may be of great scientific and practical significance in development of novel composite membrane and application of MD technology in wastewater treatment.

项目针对目前膜材料疏水性差、膜通量与机械强度较低等限制膜蒸馏技术应用的瓶颈问题，依据国内外最新发展趋势，结合申请者及研究团队已有研究成果，开展超疏水纳米纤维电纺复合膜制备及其膜蒸馏过程机理研究。研制以亲水性聚酯材料为支撑的PVDF纳米纤维亲/疏水复合膜，实现支撑层与功能层的分离，提高膜机械强度与膜通量，调控并优化复合膜分离功能层多级结构、形成超疏水膜表面；开发基衬增强-正负极同场静电纺丝新工艺，纺制机械强度高、膜通量大、表面超疏水的纳米纤维复合膜；解析复合膜功能特性，阐释膜表面类荷叶微纳米结构形成机制与超疏水膜-水界面力学作用原理。依托复合膜材料功能特性与膜分离技术优势，以高盐高有机工业废水高效资源化处理为应用目标，构建以新型复合膜为核心的膜蒸馏反应器，深入探讨亲/疏水复合膜在膜蒸馏过程的传质与传热机理，为开发新型复合膜材料及其在高效膜蒸馏分离技术中的应用提供科学依据与技术支持。

项目针对目前膜材料疏水性差、膜通量与机械强度较低等限制膜蒸馏技术应用的瓶颈问题，开展超疏水纳米纤维电纺复合膜制备及其膜蒸馏过程研究。研制出亲水性聚酯材料为支撑的PVDF纳米纤维亲/疏水复合膜，实现了支撑层与功能层的分离，提高了膜机械强度与膜通量，调控并优化复合膜分离功能层多级结构、形成了超疏水膜表面。研究考察了不同纺丝液体系对膜形貌结构与性能的影响，优化了静电纺丝过程中的工艺参数；在深入探讨静电纺丝纳米纤维膜成膜原理及优化静电纺丝工艺参数与纺丝液配比的基础上，研究了不同支撑材料与纳米颗粒对静电纺丝纳米纤维膜性能的影响，制备出了PVDF-HFP/SiNPs纳米纤维超疏水膜；以醋酸纤维素（CA）为原料，1-甲基-2-吡咯烷酮/丙酮为混合溶剂，无纺布为支撑层，将经过水解反应的正硅酸乙酯（TEOS）溶胶液原位引入到CA溶液中，采用采用静电纺丝技术与溶胶-凝胶方法，制备了醋酸纤维素/二氧化硅复合纳米纤维膜，将其浸渍于全氟烷基硅烷（FAS）/正己烷分散液中可得到CA/SiNPs-FAS超疏水复合膜。PVDF-HFP/SiNPs、CA/SiNPs-FAS纳米纤维超疏水膜具有机械强度高、膜通量大、耐污染及抗润湿等功能特性，可以维持膜蒸馏过程的长周期稳定运行，具有较大的应用前景。膜蒸馏技术在浓水处理领域具有广泛的应用前景，但膜润湿与膜污染仍然是阻碍其工业化应用的主要问题之一；项目研究了在膜蒸馏过程中表面活性剂对不同微孔疏水膜的影响机制，进料液中阴离子表面活性剂十二烷基硫酸钠(SDS)会引起严重的膜润湿现象，超疏水、疏水疏油膜具有较强的抗润湿性，而传统的PVDF、PTFE疏水膜抗润湿能力较弱；而当钙离子大量存在于进料液时，其与SDS的聚集虽可降低膜润湿程度但其在膜表面的沉积会导致严重的膜污染。界面相互作用自由能的理论计算结果表明PVDF膜与SDS胶体之间的吸引力最大、PTFE膜其次、而双疏膜最小，研究结论从理论上阐释了疏水膜污染发生机制。项目取得的研究成果，可为开发新型复合膜材料及其在高效膜蒸馏分离技术中的应用提供科学依据与技术支持。