Development of integrally skinned polysulfone ultrafiltration membrane

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Date
2005
Authors
Mahanim Sarif, @ Mohd Ali
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Abstract
This thesis focuses on the development of integrally skinned polysulfone ultrafiltration membranes and the effect of casting parameters on the membrane performance to produce a consistent and reproducible membrane. Formation of the flat sheet membrane had been performed by alteration of polymer concentration, membrane nominal thickness, evaporation time and shear rate, which were identified as dominant casting parameters in controlling skin thickness and skin integrity. In view of the fact that membrane properties and reproducibility are sensitive to the fabrication conditions, the parameters to produce a membrane should be controlled in a more precise manner which could never be achieved using conventional or manual casting process. Thus, to reduce the error of manual casting, the membrane was consistently fabricated using the lab developed Membrane Auto Casting Machine which combines the advantageous features of casting technology which enhances the production of even, smooth, ultrathin, defect-free membrane and high reproducibility. This casting machine basically consists of four major parts and all these parameters could be adjusted according to the requirements of final product. Casting solution developed in this study consisted of polysulfone (PSF) as a polymer and 1-methyl-2-pyrrolidone (NMP) as a solvent. Polyvinylpyyrolidone (PVP) was used as an additive at the preliminary stage. Effect of PSF concentration was studied as the preliminary work to find out the best formulation that gives the best performance to the membrane developed. It was found that the used of PVP with higher molecular weight, will give a good permeability but poor rejection. Thus, polyethylene glycol (PEG) with lower molecular weight was chosen to replace PVP as a new additive to increase the membrane rejection. Therefore, the formula of PSF/NMP/PEG was used in the overall research. In this study, a systematic work was carried out to investigate the effect of casting parameters including membrane thickness, evaporation time and shear rate. The optimum membrane could be fabricated under shear rate of 277.78s-1 for membrane nominal thickness of 150 m and evaporation time in the range of 10s to 15s. It was determined that the pure water permeability (PWP), PEG flux and PEG rejection were 40.52 L/m2h, 36.97 L/m2h and 73.14% respectively at those conditions. The membranes were then characterized by molecular weight cut off (MWCO), pore size distribution (PSD) and scanning electron microscopy (SEM). Finally, in order to fully realize the potential of ultrafiltration membrane and to predict the membrane performance, the flux and rejection through the membrane was predicted based on linear model equation. Both flux and rejection data were well predicted by the model, which showed only a small difference between the experimental data and calculated data. As a conclusion, the final performances of the membrane are very much depending on the casting parameters.
Description
Master
Keywords
Chemical Engineering , Plysulfone ultrafiltration membrane
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