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VIPS参数优化制备高性能膜蒸馏膜及其高矿化度矿井水处理应用

High-performance md membrane fabrication via VIPS optimization for high-salinity mine water treatment

  • 摘要: 膜蒸馏技术凭借运行压力低、可高效利用低品位热源等独特优势,在高矿化度矿井水零排放处理工艺体系中占据重要地位,是构建经济高效处理流程的关键技术单元之一,但高能量抗污染的膜蒸馏膜的欠缺阻碍了其迈向工业化应用。使用蒸汽诱导相分离(VIPS)技术取代传统液致相分离技术制备疏水微孔聚偏氟乙烯(PVDF)膜,并将其应用在膜蒸馏高矿化度矿井水处理技术中。通过对VIPS过程温度、湿度、暴露时间等参数的协同调控,实现对膜结构与性能的优化。利用扫描电镜、孔隙率测试、孔径分析仪等表征手段,监测了不同参数条件对膜结构的影响,通过响应面法综合分析多因素之间的协同作用,使用高盐模拟水与宁东矿区真实高矿化度矿井水测试了优化VIPS膜在膜蒸馏过程中的实际性能表现。结果表明:温度升高会加速VIPS过程的相分离速度,减少膜表面结节结构的形成并帮助膜形成更大的孔径与孔隙率,但过高的温度会对孔隙率的提升起到抑制作用;湿度的增加有利于提升VIPS过程中非溶剂的入侵速率,帮助增大孔径与孔隙率,提升膜通量,但过高的湿度反而会使得孔隙封闭;暴露时间主要决定相分离的进程,暴露时间过短相分离不充分,暴露时间过长会使孔隙坍缩,适宜的暴露时间帮助形成均匀且高性能的膜。参数之间还存在不同程度的相互作用,温度与暴露时间的协同作用最为显著,其次是温度与湿度,而湿度与时间之间的作用较弱。最终使用温度40 ℃、湿度70%、暴露时间15 min为优化参数制备了VIPS膜,并且使用直接接触膜蒸馏装置评估了其处理性能。测试发现膜的平均通量分别达到14.75 L/(m2·h)和14.03 L/(m2·h),截留率均在99.9%以上,并且在测试期间始终保持稳定。测试前后膜表面电镜图片显示其并未出现明显的污染物附着情况,接触角测量数据测试前后也稳定在110°左右,说明膜具有较好的抗润湿和污染能力,展现出了良好的性能。

     

    Abstract: Membrane distillation MD technology occupies an important position in the zero-discharge treatment process system of high-mineralization mine water due to its unique advantages, such as low operating pressure and the efficient utilization of low-grade heat sources. It is one of the key technical units for constructing an economical and efficient treatment process. However, the lack of high-performance MD membranes has hindered its industrial application. The vapor-induced phase separation (VIPS) technique was used to replace the traditional liquid-induced phase separation technique to prepare hydrophobic microporous polyvinylidene fluoride (PVDF) membranes, which were then applied to the membrane distillation technology for treating high-mineralization mine water. By coordinately regulating parameters such as the temperature, humidity, and exposure time during the VIPS process, the optimization of the membrane structure and performance was achieved. Using characterization methods such as scanning electron microscopy, porosity testing, and pore size analyzer, the effects of different parameter conditions on the membrane structure were monitored. The synergistic effects among multiple factors were comprehensively analyzed by the response surface method. High-salt simulated water and the actual high-mineralization mine water from the Ningdong Mining Area were used to test the actual performance of the optimized VIPS membrane during the membrane distillation process. The results indicate that: Elevating temperature accelerates the phase separation rate during VIPS, reduces the formation of nodular structures on the membrane surface, and facilitates the development of larger pore sizes and higher porosity. However, excessively high temperature constrains the enhancement of porosity. Increased humidity promotes the intrusion rate of non-solvents in VIPS, which contributes to enlarged pore sizes, elevated porosity, and improved membrane flux; conversely, excessively high humidity results in pore closure. Exposure time primarily governs the progression of phase separation: insufficient phase separation occurs with overly short exposure time, whereas pore collapse is induced by overly long exposure time. An appropriate exposure time helps to form a uniform and high-performance membrane. There are also interactions of different degrees among the parameters. The synergistic effect between temperature and exposure time is the most significant, followed by that between temperature and humidity, while the interaction between humidity and time is weak. Finally, the VIPS membrane was prepared using the optimized parameters of a temperature of 40 ℃, a humidity of 70%, and an exposure time of 15 min, and its treatment performance was evaluated using a direct contact membrane distillation device. The test results showed that the average fluxes of the membrane reached 14.75 L/(m2·h) and 14.03 L/(m2·h), respectively, and the rejection rate was above 99.9%, remaining stable throughout the test period. The scanning electron microscopy images of the membrane surface before and after the test showed no obvious attachment of pollutants, and the contact angle measurement data remained stable at around 110° before and after the test, indicating that the membrane has good anti-wetting and anti-fouling capabilities and exhibits excellent performance.

     

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