An Investigation On The Preparation Technology Of Polyethersolfone-Polyamide Composite Charged Nanofiltration Membrane

Membrane is called as a selecting barrier between two phases. It is existing at nature, especially in organisms, and is the base of life. Membrane course is a new technology which was turned up at the head of 20 century and developed fast after 1960s.It is applied in many fields.Nanofiltration (NF) is a new separation technology, it has the selective permeation for different valent ions and can retain the organics with small molecule weight. The research in this field has attracted much attention because of its important significance for the development of economy.In this paper, a new method is proposed to fabricate NF membrane. The purpose is to coat a thin polypiperazing-amide (PPA) layer onto the polyethersulfone (PES) membrane by interfacial polymerization, which has the morphology and functionality of NF.An ideal PES UF membrane to be used as the support of composite membrane was prepared by using L-S phase inversion method in this paper. The effect of several factors upon the performance of PES ultrafiltration membrane was systematically studied by carrying out the orthogonal experiments. Additionally, the model equation was established by regressing analysis. The results show that the pure water flux of polyethersulfone ultrafitration membrane is 246.9 L.m~-2 . h~-1 (Under the operating pressure of 0.1MPa) and that the membrane retention to polyvinyl alcohol solution with concentration 500ppm is more than 95%.The capability of NF membrane is lie in the interfacial polymerization (IP) reaction later. A series of pre-experiments was done for comparing different factors which determine the characterization of membrane.Compared to negative NF, positive NF has more development space. PEI and trimesoyl chloride were chosen as monomers of IP reaction and water and n-hexane were used as solvents for them. The uniform design was applied to the fabrication of the NF composite membrane and the experimental data was processed by SPSS software. The following optimized conditions were obtained: PEI concentration 1.75%(wt); SDS concentration 0.1%(wt); Reacting time 2min and acid accepters(AA) concentration 0.3%(wt). The retention of this membrane to CaCl2and MgCl2 is about 70% and the retention to NaCl and KC1 is about 30%. Moreover, the retention of this membrane to dyes with small molecule weight is more than 90%.Subsequently 2,5-diaminobenzene sulphonic acid (DABSA) was chosen as one monomer of IP reaction. The uniform design was applied to the fabrication of the NF composite membrane and the experimental data was processed by SPSS software. The following optimized conditions were obtained: DABSA concentration 0.75%(wt); SDS concentration 0.15 %(wt); acid accepters(AA) concentration 0.15%(wt)and Reacting time 3min. The retention of this membrane to CaCl2and MgCl2 is about 80% and the retention to NaCl and KC1 is about 40%. Moreover, the retention of this membrane to dyes with small molecule weight is more than 90%.At last, NF composite membrane is compared to the CA NF which is provided by the NF researcher in China. The retention of the former NF membrane to electrolyte solution is lower than that of the latter. The retention of the former to dyes with small molecule weight is higher than the latter. And the flux of the former to solution is higher than the latter.