The Effects Of Operating Parameters On Separation Performance Of Nanofiltration Membrane

Nanofiltration(NF) membranes are new kinds of membranes that have properties between those of ultrafiltration(UF) and reverse osmosis(RO). The application of nanofiltration becomes increasingly popular. γ-Al₂O₃ membrane is one of ceramic nanofiltration membranes. Its average pore size is of 2³nm. Up to now, the applications and researches of ceramic nanofiltration membranes have been still at experimental research stage, and many research efforts are needed. In this work, the effects of operation parameters on Mg²⁺ rejection and flux of permeate were tested with a lab rig that was set up by myself. In addition, a new transfer model was developed on the basis of non-balance thermodynamics model. The researches were carried out with the orthogonal experiment of 4factors. The effect factors influencing separation performance of the membrane were operating pressure, temperature of experiment, concentration of feed solution, and velocity of flow. Each factor varied at four different condition levels. The experimental results show that operating pressure and temperature of experiment are two very prominent factors influencing flux of permeate. Increasing operating pressure or temperature of experiment, flux of permeate would increase. Concentration of feed solution also has influence on flux of permeate. The higher the concentration of feed solution is, the lower the flux of permeate. In the experiments, velocity of flow is the least prominent factor. Its change has little influence on flux of permeate. The prominent factor influencing rejection is operating pressure. The effects of other factors are not so significant. The rejection increases with increasing operation pressure. On the other hand, the higher the feed concentration is, the lower the rejection. And making temperature and cross-flow velocity higher, respectively, would result in increasing rejection although rejection increases fluctuantly. In terms of general theories of membrane separation and non-balance thermodynamics model, a new transfer model was developed and proved by 16 groups of data of orthogonal experiment. At first, the model constants were determined from a group of data. Secondly, according to these constants and transfer equation of the new model, the flux of permeate in the rest of 15 experiments could be calculated. Comparing with the experimental flux of membrane, it is shown that the values calculated are very accurate. The maximum relative error is of –17.7% and the mean-root-square error is of 5.8%. In addition, the effects of membrane fouling and pH on separation performance of γ-Al2O3 membrane were discussed.