次氯酸钠清洗对超滤膜的长期损伤行为

Long-term Damage Behavior of Sodium Hypochlorite Cleaning on Ultrafiltration Membrane

次氯酸钠对超滤膜污染具有较好的清除效果,但同时也会造成膜损伤。系统探究了超滤过程中NaClO清洗对膜结构和过滤性能长期损伤的演化规律,并揭示膜损伤导致PVDF膜性能衰退机制。结果表明,模拟次氯酸钠损伤PVDF超滤膜0~6.6 a进程中,随着清洗强度增加,超滤膜截留率从87.2%下降至44.5%,膜固有阻力呈现先上升后下降的趋势,抗污染性能随之下降;扫描电镜(SEM)和膜机械性能分析显示,损伤膜表面孔洞变大,使之更容易发生断丝现象,膜的机械性能变差。结合接触角、红外光谱以及X射线光电子能谱表征可知,膜损伤过程中膜性能衰退的本质是添加剂聚乙烯吡咯烷酮(PVP)以及聚合物化学性质改变。前期亲水添加剂PVP易被解离析出,因此接触角上升;后期PVDF聚合物发生脱氟化氢效应,C—F键断裂后生成C=C,进一步反应生成羰基,进而降低膜的抗污染能力。

Sodium hypochlorite has a good removal effect on ultrafiltration membrane fouling,but it can also cause membrane damage.In this paper,we explored the evolution of long-term damage to membrane structure and filtration performance caused by NaClO cleaning during ultrafiltration,and revealed the mechanism of PVDF membrane performance degradation caused by membrane damage.The results showed that in the process of simulating sodium hypochlorite damage to PVDF ultrafiltration membrane for 0 to 6.6 years,as the cleaning intensity increased,the rejection rate of the ultrafiltration membrane decreased from 87.2%to 44.5%,the inherent resistance of the membrane first increased and then decreased,and the anti-fouling performance of the membrane decreased SEM and membrane mechanical property analysis showed that the surface pores of the damaged membrane became larger,making it more prone to breakage and deteriorating its mechanical properties.Combined with the contact angle,infrared spectroscopy and X-ray photoelectron spectroscopy,it was found that the essence of the performance degradation during the membrane damage process was the chemical properties of the additive polyvinylpyrrolidone(PVP)and the polymer.In the early stage,the hydrophilic additive PVP was easy to be dissociated and precipitated,so the contact angle increased.In the later stage,the PVDF polymer undergoed defluorination effect,and C=C was formed after the C—F bond was broken,and the carbonyl group was further reacted,which reduced the anti-fouling ability of the membrane.