Study On Preparation And Properties Of The Composite Membrane Based On PTFE Flat Membrane

So far,some achievements has been made at the the research of composite nanofiltration membrane.The composite nanofiltration membrane is usually composed of the nanofiltration functional layer and the substrate,and its performance is also determined by the two parts.Therefore,on the basis of the existing research,it is of practical significance to explore more excellent membrane materials for the higher needs in industry.In this paper,the hydrophilic modified polytetrafluoroethylene?PTFE?flat membrane was used as the substrate,triethylenetetramine?TETA?was used as the water-phase monomer and trimesoyl chloride?TMC?was used as the organic-phase monomer.TETA-TMC composite nanofiltration membrane was prepared through interfacial polymerization between TETA and TMC on the hydrophilic PTFE substrate.The effects of the preparation conditions including TMC concentration,TETA concentration,interfacial polymerization time,heat treatment temperature and heat treatment time on the separation performance of TETA-TMC composite nanofiltration membrane were investigated systematically.The chemical compositions of TETA-TMC composite nanofiltration membrane were characterized by Fourier transform infrared-attenuated total reflection?ATR-FTIR?.Field emission scanning electron microscopy?FE-SEM?was used to observe the surface microstructure of TETA-TMC composite nanofiltration membrane.Zeta potential analyzer was used to measure the charge on the surface of TETA-TMC composite nanofiltration membrane.The hydrophilicity of TETA-TMC composite nanofiltration membrane was obtained by contact angle measurement.The molecular weight cut-off?MWCO?of TETA-TMC composite nanofiltration membrane,the pure water fluxes of TETA-TMC composite nanofiltration membrane and the removal performances of four types of salts?MgCl₂,MgSO₄,Na₂SO₄,NaCl?for TETA-TMC composite nanofiltration membrane were tested by cross-flow filtration.The conclusions were as follows:?1?With the increase of TMC concentration or the prolongation of interfacial polymerization reaction time,the permeation fluxes of TETA-TMC composite nanofiltration membrane decrease firstly and then stabilize,while the rejection values increases firstly and then tend to be constant.With the increase of the TETA concentration,heat treatment temperature or the heat treatment time,the permeation fluxes of TETA-TMC composite nanofiltration membrane decrease firstly and then increase,while the rejection values increase firstly and then decreases.The research shows the optimal preparation conditions of TETA-TMC composite nanofiltration membrane were obtained as follows:the concentration of TETA,the concentration of TMC,polymerization reaction time,heat treatment temperature and heat treatment time were1.3wt%,0.8wt%,120s,70? and 15min,respectively?the concentration of aqueous phase additives including SDS and TEA were 0.05wt%,and 1.5wt%,respectively?.Under these conditions,the permeation flux of 1g/L MgSO₄ solution?feed temperature was set at 25??under the pressure of 0.4Mpa is 5.996 L·m^-2·h^-1 and the rejection value is 98.7%.?2?According to the results of ATR-FTIR measurement,polyamide have been successfully formed through the interfacial polymerization of TETA and TMC on the surface of the hydrophilic PTFE substrate;A thin and dense polyamide functional layer can be seen on the surface of PTFE substrate by FE-SEM.Zeta potential of TETA-TMC composite nanofiltration membrane was measured and its value is zero when pH is⁵.1.It indicates that TETA-TMC composite nanofiltration membrane shows a positive charge when pH is lower than 5.1;Water contact angle of TETA-TMC composite nanofiltration membrane is 54.66°,indicating it has good hydrophilicity;The molecular weight cut-off of TETA-TMC composite nanofiltration membrane was 490Da.Under the pressure of 0.4MPa,the pure water flux of TETA-TMC composite nanofiltration membrane was 7.521L·m^-2·h^-1and the rejection values follow the order of MgSO₄?MgCl₂>Na₂SO₄>NaCl.