Abstract:

Membrane distillation (MD) has the advantages of low operating pressure, operating temperature and operating cost, so it has broad application prospects in water treatment. But the wetting and fouling during the MD process will reduce the efficiency of it, which hiders its steps of industrialization. There are many factors that may lead to wetting and fouling, the existence of surfactant is one of them. Surfactant can lower the surface tension of the solution significantly, and might change the property of the feed solution as well. This research add sodium dodecyl sulfate (SDS) into the salty water as feed solution to study the effects of surfactant on direct contact membrane distillation (DCMD) process. The wetting and fouling phenomenon was studied as a function of the SDS concentration, the valence of the added electrolyte, and the different membranes. And results showed that the increase of SDS concentration would make the wetting more severe. It can also be concluded that the omniphobic membrane was the first while the PVDF membrane was the last in an order of the resistance to wetting. When changing NaCl into CaCl₂, the aggregations of Ca²⁺ and SDS weaken the wetting phenomenon but their deposits on membrane lead a fouling. The interaction energies between the colloid and the membrane surface were calculated. And the data manifested that the attraction of PVDF membrane was the largest while the omniphobic membrane was the smallest, which was consistent with the experimental results.

Key words: membrane, distillation, surfactant, membrane fouling, membrane wetting

摘要：

膜蒸馏具有较低的操作压力、操作温度以及运行成本等优点，因此在水处理方面有广泛的应用前景。但是膜蒸馏过程中的膜润湿和膜污染现象仍然是阻碍其工业化应用的主要问题。表面活性剂作为一种能显著降低溶液表面张力、改变进料液性质的物质，对膜蒸馏造成的影响值得被研究。基于此，研究了在直接接触式膜蒸馏（DCMD）过程中表面活性剂对不同商业微孔疏水膜造成的影响，选用了一种常见的阴离子表面活性剂十二烷基硫酸钠(SDS)进行实验。结果表明，进料液中SDS浓度的上升会引起更为严重的膜润湿现象，并且所使用的三种商业膜中，双疏膜抗润湿性最强，而PVDF膜最弱。而当Ca²⁺大量存在于进料液中时，Ca²⁺与SDS的聚集降低了膜润湿的程度但其在膜表面的沉积造成了严重的膜污染。界面相互作用自由能的计算结果表明Ca²⁺/SDS与PVDF膜之间的吸引力最大、PTFE膜其次、双疏膜最小，这一结果与膜蒸馏过程中通量变化情况相符。

关键词: 膜, 蒸馏, 表面活性剂, 膜润湿, 膜污染