真空膜蒸馏中的膜污染研究

Study on membrane fouling in vacuum membrane distillation

用场发射扫描电子显微镜（FESEM）结合能谱分析（EDS）表征真空膜蒸馏过程中的聚偏氟乙烯（PVDF）中空纤维膜的污染情况。膜污染物是含Na、Cl、Si、Mn、Fe、Cu和Zn等元素的混合物,各元素分布密度从膜外侧向内侧为递减趋势。据此确定的清洗方案为：在45℃、pH 2~3的稀盐酸溶液中浸泡2h,然后在45℃、5000ppm的次氯酸钠水溶液中清洗2h,最后在45℃下进行烘干来恢复PVDF中空纤维膜的稳定性能,并反复多次清洗和多次进行VMD稳定实验。结果表明：按此清洗方案以间隔20h清洗一次的频率进行膜蒸馏系统的维护,可以使膜蒸馏系统长期稳定运行。

The morphology and fouling of the PVDF hollow fibre membrane used for vacuum membrane distillation（VMD）were studied by FESEM and EDS.The element analysis of membrane foulant using FESEM-EDS indicated that Na,Cl,Si,Mn,Fe,Cu and Zn consisted of the inorganic elements,and the density distribution of these elements decreased from outside to inside of hollow fiber membrane.Based on the membrane fouling analysis,a cleaning process was employed for fouling control.It involved cleaning hollow fibers in HCl of pH 2~3at 45℃for 2h,NaOCl of 5000mg/L,pH 11 at 45℃for 2h,and drying in vacuum oven at 45℃.The experiments,which looped the procedure of every 20 hdesalination followed by an above mentioned cleaning program revealed that desalination with VMD process powered by hydrophobic PVDF hollow fiber membrane can be stably operated for a relatively long period.