New Preparation Process Of Charged Mosaic Membrane And Its Performance Characterization

Charged mosaic membrane (CMM) contains both anion and cation exchange groups, which provide a continuous pathway for electrolyte to permeate. Therefore, CMM can be permeable to salts but meanwhile not to low-molecular-weight non-electrolytes. During the former period, we have prepared well-performed CMM. New interfacial polymerization (IP) monomer was used to try to achieve the match between anion and cation exchange groups based on the former research and to improve the membrane separation performance and reduce the experiment cost. On the other hand, the cheaper n-hexane was adopted for organic solvent. In the paper, IPwas used to polymerized a very thin selective layer on polyethersulfone (PES) ultrafiltration supporting membrane , which had the structure and character of CMM.In order to prepare CMM, supporting membrane had been prepared. The material and core have a effect on composite membrane. So the influential factors upon the performance of PES ultrafiltration membrane was systematically studied through carrying out the orthogonal experiments. we obtained the optimized condition for making the support membrane as follow: PES concentration in casting solution 14%(wt); PEG400 concentration in casting solution 10%(wt),PVP concentration in casting solution 6%(wt); and evaporating time 5s.The result show that the pure water flux of PES ultrafitration membrane is 230.6 L·m^-2·L and the membrane retention to PVA88000 solution with concerntration 500 mg/L is more than 90%(Under the operating pressure of 0.1Mpa). Then, this will establish certain foundation for later study of the preparationof the composite membrane.The mixture of 2, 5-diaminobenzene sulfonic acid (DIA) and polyetherimide (PEI)was chosen as one monomer of IP reaction, and trimesoyl chloride (TMC) as another monomer. For the IP process investigated, n-hexane and water was used as solvents for TMC and DIA respectively. In this paper the uniform design was applied to the fabrication of the CMM composite membrane and the experimental data was processed by SPSS software. The following optimized conditions were obtained: PEI concentration 0.8%(wt);DIA concentration 0.75%(wt);SDS concentration 0.1 %(wt) ;IP reacting time 2 min. The CMM composite membrane was prepared on the condition above and permeation experiments of this membrane were performed using electrolyte and non-electrolyte solution. The retention of this membrane to PEG1000 is more than 90% and the retention to inorganic salts is less than 30%,and the separation factor for PEG1000/NaCl is 4.8. It was shown that both volume flux and rejection increase with increasing the operation pressure, and decrease with the increase of the solution concentration.Based on the experimental results, the structural parameters of the CMM composite membrane (the pore radius and the ratio of the membrane porosity to the membrane thickness) were discussed on the basis of the pore model. The average pore size of the composite selective layer of the CMM membrane is 2.44 nm, and the ratio of the membrane porosity to the membrane thickness is 2.04×10⁵ m^-1.