Preparation And Characterization Of Charged Nanofiltration Membrane

Nanofiltration(NF) is a kind of pressure-driven membrane separation technology, which is between reverse osmosis (RO) and ultrafiltration(UF). It has the selective permeation for different valent ions and can be used to separate the organic molecules from water. The research in this field has attracted much attention because of itsimportant significance for the development of economy.In this paper a method was proposed to fabricate NF composite membrane, which used interfacial polymerization techniques to deposit a thin selective layer onto a porous support (PSF ultrafiltration membrane). Through the experiments we obtained the optimized conditions for making the support membrane as follows: PSF concentration in casting solution 13%(wt); PVP concentration in casting solution 10%(wt);Acetone concentration in casting solution 0.6%(wt) and Evaporating time 30s.On the condition above a PSF support membrane was fabricated which has the satisfactory water flux and retention to PVA 80000 at the pressure of 0.2Mpa,that is ,274.9 L m-2 h-1 bar-1 and 95% respectively.The mixture of 2,5-diaminobenzene sulphonic acid (DABSA) and 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 DABSA, respectively. In this paper 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 1.5%(wt); Reacting time 3min;DABSA concentration 0.25%(wt);SDS concentration 0.15 %(wt) and acid accepters(AA) concentration 0.15%(wt).The NF 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 CaCl2 is more than 90% and the retention to NaCl is less than 50%. Moreover, the retention of this membrane to polyethyleneglycol (PEG) 1000 is more than 95%.It was shown that both volume flux and rejection increase with increasing theapplied pressure, and decrease with the increase of the electrolyte solution concentration.Based on the experimental results, the structural parameters of the NF composite membrane (the pore radius and the ratio of the membrane porosity to the membrane thickness) were discussed on the basis of the fixed-charge model and the pore model. The average pore size of the composite selective layer of the NF membrane was determined by using the surface area and pore size analyzers as about 2nm.In order to examine the stability of DABSA concentration with time, the absorbency test of DABSA solution was performed. Moreover, the analysis method of PEG concentration with various molecular weight was carried out by using a ultraviolet spectrophotometer for testing the effect of chromogenic reaction time and the amount of chromogenic reagent. The optimal testing condition is as follows: The amount of Iodine and BaCl2 is 1.0ml and 1.2ml, respectively. And the chromogenic reaction time is between 1200 seconds and 1400 seconds.