The Effect Of The Additives In The Aqueous Phase On Structure And Performance Of The Polyamide Thin-film Composite Membrane

Nanofiltration is a new type of membrane separation technology between ultrafiltration and reverse osmosis developed in the late 1980 s.It has high desalination rate for bivalent ion and the organic with the relative molecular weight between 200-1000 Da. Nanofiltration membranes have been widely applied to medicine and health,food, water treatment and environmental protection fields and so on,due to its unique separation and lower operating pressure. However, the low flux and membrane fouling problem make the nanofiltration membranes are constrained in the practical applization.Aromatic polyamide composite nanofiltration membranes prepared through interfacial polymerization between m-phenylenediamine(MPD) and trimesoyl chloride(TMC) has higher desalination rate. However,the membrane has low flux,because of the ultra-thin poly skin layer structureb has a higher degree of crosslinking. In this paper, Polyamide thin-film composite membrane was prepared through interfacial polymerization between m-phenylenediamine(MPD) and trimesoyl chloride(TMC) on the polysulfone(PSF)support membrane.The method of improved composite nanofiltration membrane performance was researched mainly from the point of introduced additives in the aqueous phase and optimized interfacial polymerization conditions.The effect of surfactants,the composite catalyst and hydrophilic additives as well as the reaction conditions on the ultra-thin poly skin layer structure and performance of the nanofiltration membrane were systematically investigated. Separation performance and stability of the composite nanofiltration membrane were evaluated. This paper aimed at preparing of Aromatic polyamide composite nanofiltration membranes with high flux and certain desalination rateunder low pressure. The main The main conclusions are as follow:(1)Sodium dodecyl sulfate(SLS) were selected as surfactant.The effect of SLS on the ultra-thin poly skin layer structure and performance of the nanofiltration membrane were systematically investigated. Results show that the degree of the ultra-thin skin layer crosslinking increased,the surface roughness increased, the hydrophilicity contact angle decreased, and the water flux decreased,as well as the rejection increased, as the concentration of SLS increased from 0 wt % to 1 wt %. When the concentration of SLS is 0.2 wt%, the composite nanofiltration membrane exhibited the water flux of 7 L·m-2·h-1 and rejection of 93.4% to 2000 mg/L Mg SO4 solution under 0.6 MPa.(2)The effect of the composite catalyst(triethylamine(TEA) and camphorsulfonic acid(CSA)), as well as the reaction conditions on the ultra-thin poly skin layer structure and performance of the nanofiltration membrane were systematically investigated. Results show that the ultra-thin skin layer density increased, the surface roughness and the hydrophilicity contact angle decreased, and the water flux increased dramatically, while the changes to the rejection and the selecting sequence for salt of nanofiltration membrane have been very minor, as the TEA concentration in the composite catalyst increased from 0.5 wt % to 3 wt % and the molar ratio of TEA and CSA fixed at 1/2. When the concentration of TEA is 2 wt%, the soaking time in aqueous phase is 3 min,reaction time is 40 s, curing temperature is 80°C, curing time is 3 min,the composite nanofiltration membrane exhibited good performance that the rejection of 2000 mg/L Mg SO4 solution was 93.2%, and the water flux was 16 L/m2 h. Polyamide thin-film composite separation performance was stable at 0.2 ~ 1.0 MPa.(3) 4-(2-hydroxyethyl) morpholine were selected as hydrophilic additives.The effect of the 4-(2-hydroxyethyl) morpholine and the reaction conditions on the ultra-thin poly skin layer structure and performance of the nanofiltration membrane were systematically investigated. Results show that the ultra-thin skin layer density and thickness decreased, the surface roughness and the hydrophilicity contact angle decreased, and the water flux increased dramatically,as well as the rejection decreased, while the changes to the selecting sequence for salt of nanofiltration membrane have been very minor, as the 4-(2-hydroxyethyl) morpholine concentration in the aqueous phase solution increased from 0 wt % to 5 wt %. When the concentration of 4-(2-hydroxyethyl) morpholine is 2.5 wt%, the soaking time in aqueous phase is 3 min,reaction time is 30 s, curing temperature is 80°C, curing time is 3 min,the composite nanofiltration membrane exhibited good performance that the rejection of 2000 mg/L Mg SO4 solution was 82.7%, and the water flux was 24 L/m2 h. Polyamide thin-film composite separation performance was stable at 0.2 ~ 1.0 MPa.