Preparation And Properties Of Non-woven Supported Forward Osmosis Membrane

As a membrane separation technology,Forward osmosis(FO)technology has the characteristics of low membrane fouling,low energy consumption and so on.It has broad prospects for development in the fields of food processing,seawater desalination,and salt difference power generation.The FO membrane is the core of the FO technology.The performance of the FO membrane directly affects the efficiency of the FO process.Wet non-woven fabrics(NWF)have high porosity,adjustable aperture,etc.They are widely used in battery separators,reverse osmosis and other fields.In this paper,the thin-film composite(TFC)FO membrane were prepared by interfacial polymerization with a thin-film polyamide layer on the polyethylene terephthalate(PET)NWF substrates.The effect of different PET NWF on the performance of TFC FO membrane was investigated.The working principle of TFC FO membrane was studied during the simulated seawater desalination.And the membrane surface fouling process and the ability of anti-fouling of the TFC FO membrane during the test were studied.It was found that when the preparation conditions are the same,as the thickness of the support layer decreases,the water flux and salt flux of the TFC FO membrane gradually increase,the salt rejection of the membrane decreases slightly,and the water flux of the TFC FO-3 membrane with a thin PET NWF support layer reaches 138.93 L/(m~2·h).When the average pore size of the PET NWF support layer gradually decreased,the water flux and salt flux of the TFC FO membrane gradually decreased,the water flux of the TFC FO-4membrane was 20.59 L/(m~2·h),and the salt rejection rate was as high as 99.46%.Under the same conditions,the water flux of commercial FO film was 15.314L/(m~2·h),and the salt rejection rate was 99.975%.Comparing the properties of the commercial FO membrane and the TFC FO membrane,it can be seen that the PET NWF supported forward osmosis membrane has superior overall performance.When TFC FO membrane is used to simulate seawater desalination,decreasing the thickness of the support layer or increasing the average pore size of the support layer is beneficial to the improvement of the water flux of the TFC FO membrane.The rejection of different salt ions by TFC FO membranes was higher than 90%.By SEM analysis of the surface morphology of the membrane,it can be seen that the surface of the TFC FO membrane exhibited different degrees of inorganic contamination during the experiment.In the dynamic membrane fouling test,the water flux of the TFC FO membrane was decreased in different degrees.After the physical cleaning,the water flux recovery efficiency of the TFC FO-6 membrane is higher than that of the TFC FO-4 and FO-5 membranes,indicating that the TFC FO-6 membrane has a lower tendency of membrane fouling than TFC FO-4 and FO-5 membranes.The CLSM characterization showed that with the increase of the experimental time,the polysaccharide contaminants on the surface of the membrane gradually increased and the sediment formed a dense polysaccharide contamination layer.The surface characteristics of membranes such as hydrophilicity,roughness and surface topography,and solute back-mixing during forward osmosis were analyzed.The results of membrane fouling experiments showed that solute back-mixing and hydrophilicity of the membrane surface were not influencing the trend of membrane fouling.The TFC FO membrane with high surface roughness has a higher tendency of membrane fouling,and the rough surface promotes the deposition of pollutants and forms a more intense membrane fouling.The difference in the surface morphology of the PA layer of the TFC FO membrane also affects the trend of TFC FO membrane fouling.The TFC FO film with a relatively dense PA layer and a high surface roughness has a higher fouling tendency.Four typical membrane fouling models were used to analyze the membrane fouling process of TFC FO membrane during the process of dynamic membrane fouling.The mathematical expression of typical membrane fouling model was used to fit the water flux decline of TFC FO membrane.Comparing the fitting coefficient of the TFC FO membrane with the membrane fouling model and the fouling coefficient corresponding to the membrane fouling model,it can be seen that the standard blocking model fitted the TFC FO-4 membrane well.The fouling of the cake filtration of the TFC FO-5 membrane mainly occurred,while the four membrane fouling processes of the TFC FO-6 membrane coexisted in the process of membrane fouling,and irreversible pollution was relatively rare.By analyzing the surface morphology and characteristics of TFC FO membranes,it is believed that the main membrane fouling types of TFC FO-4,FO-5 and FO-6 membranes during the dynamic membrane fouling process are different because the TFC FO membranes have different surface topographies and surface characteristics such as surface roughness.The experimental results show that the surface structure and properties of the support layer have a direct and obvious effect on the TFC FO membrane fouling.When optimizing the performance of TFC FO membrane,it is necessary not only to fully consider the influence of the support layer structure on the concentration polarization in the FO process,but also to investigate the influence of the support layer characteristics on the surface morphology and the pollution trend of the TFC FO membrane.