解读纳滤:一种具有纳米尺度效应的分子分离操作

纳滤膜是20世纪80年代末期发展起来的一种广泛用于液体分离的新型分离膜。早期研究中,先后提出的基于筛分效应的细孔模型,基于静电效应的电荷模型,以及同时考虑上述两种效应的静电位阻模型和道南位阻模型等为人们更好地理解纳滤膜分离机理和指导纳滤膜过程应用发挥了十分重要的作用。然而由于这些具有“疏松型反渗透膜”特点的纳滤膜没有相应的膜性能预测评价软件,使得针对具体应用过程的纳滤膜的大规模标准化应用受到了一定的制约。为此,结合上述模型,根据一些特定实验拟合确定混合盐体系同号离子间的竞争作用和异号离子间的调节作用,提出了一个适于混合盐体系的纳滤膜分离性能评价模型,促进了纳滤膜技术在水处理过程的大规模推广。最近,根据纳滤膜对离子选择性分离性能及其伴随的动电性质的细致而深入的实验研究,发现仅考虑筛分效应和静电效应并不能完全合理地解释纳滤膜的分离性能,且在动电性质的解析上也存在一定缺陷,进而对纳滤膜纳米级孔径引起的特殊效应和溶液体系中复杂相互作用引起的荷电性质变化有了更为深刻的认识和理解,提出并定量分析了离子透过纳滤膜时存在的介电排斥效应。

Nanofiltration Understanding: A Separation Process of Molecular-Level with Nano-Scale Effect

Nanofiltration(NF) membrane has been developed from the late 1980s and widely applied in the separation of liquid mixtures.Several models for NF process have been proposed,such as the pore model based on the sieving effect,the charge models based on the electrostatic effect,and the electrostatic steric-hindrance model and the Donnan steric pore model based on the both effects,which play an important role in understanding the separation mechanism and promoting the application of NF.However,the performances of these NF membranes with features of "loose RO membranes" cannot be predicted by commercial RO simulation software,which is a severe restriction on straightforward implementation of large-scale NF applications.In regard to these problems,a model was proposed for the separation performance of mixed salts solution across NF membranes to promote the application of NF during the water treatment in the light of the competitive effect among co-ions and regulation effect among counter-ions.Both two effects can be determined by some specific experiments.Recently,based on the in-depth experimental studies on rejection performance and the attendant electrokinetic properties,some researchers have found that the performance of NF membranes cannot be predicted completely by merely considering the sieving and electrostatic effect,but some drawbacks still exist in the analysis of electrokinetic properties.The further studies have contributed to a deeper understanding on the particular effect caused by the nano-scale pore size and charge features caused by the complicated interaction in solution.Moreover,the dielectric effect in the transport process of ions through NF membranes has been addressed and quantitatively analyzed.