Study On The Preparation And Desalination Performances Of Polyamide Pervaporation Composite Membrane

Highly concentrated brine is usually referred to as the concentrated solution produced by reverse osmosis of industrial wastewater or brackish water and seawater,which is a potential alternative water source.However,the current mainstream reverse osmosis technology is not suitable for desalination of high concentration brine,because of the need for high osmotic pressure and low desalination efficiency.Since pervaporation technology is not restricted by osmotic pressure,it can purify highly concentrated brine and reduce the discharge of concentrated brine,but it has the disadvantage of low osmotic flux.In this study,TFC membrane was prepared by regulating the permeability of the supporting layer and improving the hydrophilicity of the dense layer,so as to improve the flux performance of the pervaporation desalination membrane.The PA/PES composite membranes were prepared by interfacial polymerization,which can prepare ultra-thin dense layers.However,the water permeability of the dense layer prepared by the reaction monomers PEI and TMC is low,which is not conducive to the increase of flux.In order to solve this problem,the hydrophilic polymer polyvinyl alcohol is introduced into the aqueous solution to regulate the interphase polymerization reaction rate,so that part of the polyvinyl alcohol is involved in the polymerization reaction,reducing the degree of crosslinking of the dense layer and increasing the hydrophilicity and permeability of the membrane.Finally,under the condition of 70 and 3.5wt.%Na Cl feed,the water flux of pervaporation of PA/PES composite membrane was 54.72±2.4 kg·m^-2·h^-1,and the salt rejection was 99.97%.In order to further increase the flux,the influence of mass transfer resistance caused by the supporting layer was analyzed.The pore size of PDA/PTFE support layer was 31.51 nm and the porosity was 17.76%by adjusting the modified solvent and time.The permeability of this support layer is much higher than that of PES support layer prepared by NIPS method.PA dense layer with controllable thickness was prepared by spraying assisted interfacial polymerization.Finally,under the condition of70 and 3.5 wt.%Na Cl feed,the pervaporation water flux of PA/PDA/PTFE composite membrane was 168.9±3.9 kg·m^-2·h^-1,and the salt rejection was 99.99%.At 20 wt.%feed concentration,the water flux was still as high as 94.9±4.9 kg·m^-2·h^-1.In addition,the interlaminar peeling strength of the supporting layer and the dense layer of the composite film is up to 8.5±0.5 N/cm,indicating that the composite film has good overall structural stability,which is due to the good interface adhesion of the PDA intermediate layer.