Preparation And Separation Performance Of Three Reverse Osmosis Composite Membranes By Low Temperature Plasma Treatment/Polymerization

Reverse osmosis,as an efficient and energy-saving separation technology,has become the mainstream technology for desalinizing seawater and brackish water in the market.Reverse osmosis membrane is the core device of reverse osmosis technology.Preparation of high-performance reverse osmosis composite membrane is particularly important for the development of reverse osmosis technology.At present,common aromatic polyamide reverse osmosis composite membranes generally have the defects of small selection range of polymerized monomers,complex film forming process,easy pollution and easy oxidation.Low temperature plasma is widely used in polymer surface polymerization and other fields as an efficient and environmentally friendly technology.Compared with other film forming technologies,plasma polymerization does not strictly require monomers to have unsaturated units or two or more characteristic functional groups,thus widening the selection range of polymerized monomers.The polymer film produced has a high density network structure,good adhesion to the substrate,good film strength and stability,simple film forming process and no pollution.It provides a new research direction for the preparation of high performance reverse osmosis composite films.According to its inspiration,polysulfone(PS)ultrafiltration membrane was used as the base membrane in this study,and the following three new membrane preparation methods were adopted to prepare reverse osmosis composite membranes with high salt rejection rate and high water flux:(1)reverse osmosis composite membranes were prepared by radio frequency plasma polymerization;(2)preparing a reverse osmosis composite membrane by adopting DBD plasma polymerization;(3)Using DBD plasma and traditional interfacial polymerization to prepare reverse osmosis composite membrane.Firstly,allylamine(AAM)and 3-butenenitrile(3-BN)were used as polymerization monomers respectively,and radio frequency plasma polymerization technology was used to generate ultra-thin polymer skins on the surface of polysulfone ultrafiltration membranes.In this experiment,the contact time,discharge current and discharge time of the polymerized monomer and the basement membrane were selected as influencing factors,and the salt rejection rate and water flux were used as characterization indexes of the separation performance of the composite membrane.Through regression analysis of uniform experimental results by SPSS software,the corresponding regression equation and factor interaction response surface diagram were obtained.The relationship between various influencing factors and separation performance of composite membrane was studied,and the best experimental conditions were obtained.The best experimental conditions of allylamine RF plasma polymerization reverse osmosis composite membrane are contact time 2h,discharge current 6A and discharge time 7min;The best experimental conditions for 3-BN RF plasma polymerization reverse osmosis composite membrane are contact time of 1h,discharge current of 4A and discharge time of 7min.Although the separation performance of the composite membrane is higher than that before polymerization,the rejection rate of the composite membrane to salt is still not significant due to factors such as non-continuous monomer supply and unstable discharge,and further research is needed.Secondly,AAM and 3-BN are used as polymerized monomers respectively,and DBD plasma polymerization technology is adopted to deposit polymerized monomers on the surface of the base film to form an ultra-thin skin layer.In this experiment,discharge voltage,discharge duration and monomer temperature are taken as influencing factors,and salt rejection rate and water flux are taken as evaluation indexes for separation performance of composite membrane.Because there are few related reports at home and abroad,this experiment firstly adopts several groups of single factor tests to roughly determine the range of each influencing factor,then designs corresponding orthogonal tests to further study the relationship between each influencing factor and the separation performance of the composite membrane,and determines the best process conditions through analysis.The optimal process conditions for preparing reverse osmosis composite membrane by plasma polymerization of AAM DBD are discharge voltage of 28 V,discharge time of 100 s and monomer temperature of 30?;The optimal process conditions for preparing reverse osmosis composite membrane by plasma polymerization of 3-BN DBD are discharge voltage of 28 V,discharge time of 100 s and monomer temperature of 25?.Due to the non-uniformity of DBD discharge and the instability of monomer flow,there are defects in the skin layer of the composite membrane,and the salt rejection rate is low.The experimental process needs to be improved to prepare a reverse osmosis composite membrane with higher performance.Finally,the polysulfone membrane was pretreated by DBD plasma,and then the polyamide composite membrane was prepared by interfacial polymerization with m-phenylenediamine(MPD)and trimethylbenzene chloride(TMC)as water phase and oil phase monomers respectively.After the reaction,the composite film was treated by DBD plasma again.In this experiment,discharge duration,discharge voltage,concentration of water phase monomer,concentration ratio of water and oil phase,air drying time of oil phase,air drying ratio of water and oil phase,reaction time of water and oil phase,heat treatment duration and heat treatment temperature were selected as the influencing factors.After the completion of the experiment,the results of the combined factor experiment were substituted into the single factor uniform experiment table,and the selected significant factor combination was analyzed by SPSS software.Through the regression results,the relationship between the factors and the separation performance of the composite membrane was further explored.