| In recent years,nanofiltration(NF) membranes were paid attention by the researchers in separation membrane field,because of their low operation pressure,nanometer porous structure and unique separation functions for aqueous solutions containing solvents with hundreds of molecular weights and multivalent ions.In this work,PES,PI and PES/PI alloy NF membranes were prepared by immersion precipitation phase inversion technique using acetone,propanols and PVP as additives, respectively.The effect of composition of the casting solutions and process conditions on the performances of NF membranes was investigated.It was found that,with the increase of polymer concentration,the rejection to PEG1000 increased,but both the porosity and flux of the membranes decreased.Adding additives can weaken the thermodynamic stability of the casting solution,and induce the process of phase separation to be easy.The maximum content of micromolecular nonsolvent additives in the casting solution was obtained by the cloudy point testing,it was found that the ability of leading to turbidity of the micromolecular nonsolvent additives decreased as follows:iso-propanol＞n-propanol＞acetone.According the results of the separation experiments for PEG1000,it was found that the flux of the membranes decreased and the rejection increased by adding acetone in casting solution.However,the result was opposite when the propanols were taken as additives.When the approaching ratio of propanols was over 0.8,there were different trends for the effect of n-propanol and iso-propanol on the flux of the membranes:the flux of the membranes prepared with adding n-propanol decreased but the flux kept increasing when adding iso-propanol.When PVP was added into the casting solution,the case became complicated.Adding PVP in the casting solution not only weakened the stability of casting solution,but also changed the rule of effects of propanols on the separation performance:the flux of the membranes with n-propanol as additives kept increasing when the approaching ratio of propanols was over 0.8.On the contrary,the flux with iso-propaaol decreased.By studying the difference of solubility parameters between two components in the casting system,it was found that there was relation between the effect of additives on membrane performance and the interaction between components in the casting system.The influence of evaporation time and coagulation temperature on the performance of NF membrane is also examined.The results showed that both increases of evaporation time and decreases of coagulation temperature made the flux decreased and the rejection increased.The influence of ambient temperature on the separation performance was firstly investigated in this dissertation.The results showed that increasing ambient temperature enhanced the rejection greatly.The effect of ambient temperature couldn't be ignored.On the basis of the above results,the alloy NF membranes were prepared by changing the mass ratio of PES to PI.It was found that with the increase of PES content,the flux of alloy NF membrane firstly increased and then decreased,but the trend of the rejection was opposite. The separation performance of the membranes with 7%of PES content was better.The alloy NF membrane was used for the experiment of separating and purifying benzylpenicillin sodium.It showed that the self-made alloy NF membrane had a good separating performance for benzylpenicillin sodium.The average rejection was over 40%.The flux of the membrane increased with the increases of operating pressure and the rejection decreased.When the concentration of the feed was 20g·L-1,the dimmer of benzylpenicillin sodium formed on the surface of the membrane due to concentration polarization,which made the rejection increased rapidly under 0.8MPa.When the concentration of the feed increased,the flux decreased but the rejection increased.Compared with other NF membranes reported in some articles,the performance of the alloy NF membranes prepared by blending was excellent.The results of this dissertation provide theoretical foundation for optimization of NF membrane preparation process.It is proved that the control of average pore size of NF membrane achieving by changing the compatibility of polymers is feasible.
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