| Compared with other membrane separation technologies,nanofiltration membrane has the advantages of low energy consumption,good rejection rate and permeation flux.At present,in order to kill the organic pollutants in the separation system,a certain concentration of active chlorine solution is usually added in the pretreatment process,which can effectively alleviate the biological pollution of the membrane.However,chloride ions can break and degrade the structure of polyamide,reducing the service life of the composite nanofiltration membrane.Therefore,it is necessary to improve the chlorine resistance of the nanofiltration membrane.This article uses hydrophilic polytetrafluoroethylene（PTFE）as the base membrane,piperazine（PIP）as the water phase monomer,trimesoyl chloride（TMC）as the oil phase monomer,glutaraldehyde（GA）,m-aminoacetyl as the modified monomer.First,PIP reacts with TMC to form a polyamide active layer,then glutaraldehyde is used for cross-linking reaction,Finally,the crosslinked polyamide active layer is grafted with m-aminoacetanilide to prepare the chlorine-resistant composite nanofiltration membrane.The separation performance was tested by the cross-flow filtration device,and the main process factors such as the concentration of glutaraldehyde,the crosslinking time of glutaraldehyde,the concentration of m-aminoacetanilide monomer,the grafting time of m-aminoacetanilide monomer,the heat treatment temperature,and the heat treatment time were studied respectively.The separation performance of the filter membrane and the separation performance after chlorination treatment are the best conditions for preparing the chlorine-resistant composite nanofiltration membrane;FTIR,scanning electron microscope（FE-SEM）,solid Zeta potential tester,water contact angle measuring instrument and other instruments were used to study the surface chemical structure,surface micro-morphology,nuclear charge and hydrophilicity of the chlorine-resistant composite nanofiltration membrane.The cross-flow filtration device was used to test the molecular weight cut-off,pure water flux,separation performance of four different salt solutions,and dye separation performance of the chlorine-resistant composite nanofiltration membrane.The chlorine-resistant composite nanofiltration membrane was chlorinated by standing soaking in Na Cl O solution.The separation performance of the composite nanofiltration membrane was tested before and after the chlorination treatment,and its chlorine resistance was analyzed.Get the following conclusions:（1）In the process of preparing the chlorine-resistant composite nanofiltration membrane,as the concentration of glutaraldehyde increases,the reaction time is prolonged.The rejection rate of the chlorine-resistant composite nanofiltration membrane for Mg SO4 before and after the chlorination treatment first increases and then decreases,and the flux gradually reduce.With the increase of the concentration of m-aminoacetanilide,the rejection rate of Mg SO4before and after the chlorination treatment of the chlorine-resistant composite nanofiltration membrane first increased and then decreased,and the flux first decreased and then increased.With the extension of the reaction time of m-aminoacetanilide,the retention rate of Mg SO4 before and after the chlorination treatment of the chlorine-resistant composite nanofiltration membrane first increased and then decreased,and the flux first increased and then decreased.With the increase of the heat treatment temperature and the extension of the heat treatment time,the rejection rate of Mg SO4before and after the chlorination treatment of the chlorine-resistant composite nanofiltration membrane first increased and then decreased,and the flux first decreased and then increased.Synthesize the influence of various preparation conditions on membrane separation performance and chlorine resistance.The optimal preparation conditions for the chlorine-resistant composite nanofiltration membrane were determined as follows:GA concentration is 0.1 wt%,reaction time is 1.5 h,m-aminoacetanilide concentration is 1.5 wt%,reaction time is 1 h,heat treatment temperature is 50℃,The heat treatment time is 10 min;（2）FTIR analysis showed that:glutaraldehyde and meta-aminoacetanilide reacted with the polyamide active layer;SEM showed that fine particles appeared on the surface of the chlorine-resistant composite nanofiltration membrane,showing a rougher state;through solid Zeta analysis The instrument shows that the potential of the chlorine-resistant composite nanofiltration membrane is-10.26 m V（±2.64 m V）,and the negative chargeability is lower than that of the PIP/TMC composite nanofiltration membrane;the water contact angle shows that the chlorine-resistant composite nanofiltration membrane is 12.6 °,which has a certain hydrophilic.（3）As the operating pressure rises to 0.6 Mpa,the pure water flux of the chlorine-resistant composite nanofiltration membrane rises to 29.09 L/m2·h;the molecular weight cut-off of the chlorine-resistant composite nanofiltration membrane is 610 Da;The order of the rejection rate of salt is:Mg SO4>Na2SO4>Mg Cl2>Na Cl;the order of the rejection rate of the three dyes is:methyl blue（97.6%）>Congo red（96.5%）>crystal violet（91.5%）;（4）The chlorine-resistant composite nanofiltration membrane has better chlorine resistance than other monomer composite nanofiltration membranes.It is immersed in a Na Cl O solution（p H=4）with a concentration of 1000 mg/L for 10 h,The retention rate of the chlorine-resistant composite nanofiltration membrane for Mg SO4is kept above 90%,and the rejection rate of Mg SO4 by the PIP/TMC composite nanofiltration membrane was reduced from 94.60%to78.85%.When other monomer composite membranes were immersed in 500 mg/L Na Cl O solution（p H=4）for 2 h,the rejection rate of MPD/TMC composite nanofiltration membranes decreased from 96.10%to 32.08%after chlorination,and the water flux decreased from 6.79L/m2·h dropped rapidly to 0.72 L/m2·h;the rejection rate of the PEI/TMC composite nanofiltration membrane dropped from 93.75%to 12.00%,and the water flux rose rapidly from11.25 L/m2·h to 63.18 L/m2·h.In summary,the chlorine-resistant composite nanofiltration membrane has certain chlorine resistance. |
