| Membrane separation is a new green and efficient separation technology.With the development of membrane technology,it is more and more widely used in industrial applications.As a component of ultrafiltration,Ultrafiltration membrane plays a key role in the separation process.At present,there are many researches on ultrafiltration membranes,but there are few reports on ultrafiltration membranes with low molecular weight cut off.Moreover,the low molecular weight ultrafiltration membranes on the market have low water flux,poor hydrophilicity and vulnerability to pollution.Therefore,it is necessary to explore the preparation of low molecular weight ultrafiltration membranes with better performance.In this experiment,polyethersulfone?PES?was used as membrane material,N,N-Dimethylacetamide?DMAC?as solvent,organic small molecule acid?Sorbic acid,Trimesic acid,Pyromellitic acid?as additives,pure water as gel bath.Prepare a series casting solutions with different proportions.By immersion precipitation phase transformation method to prepare PES base membranes.Field emission scanning electron microscopy?SEM?,contact angle measuring instrument,X-ray photoelectron spectroscopy?XPS?and ultrafiltration device were used to evaluate the performance and structure of the membrane.The effects of PES concentration and different additives on the structure and properties of the membrane were investigated.With the increase of PES concentration,the viscosity of the casting solution increased,the pore size of the membrane became smaller,and the pure water flux decreased.After adding the additives,the hydrophilicity of the membrane surface increases.With the increase of sorbic acid,trimesic acid?TMA?and pyromellitic acid?PMA?,the pore size and pure water flux of membrane surface increased in varying degrees.Compared to sorbic acid and TMA,the membrane with PMA has larger surface pore size and pure water flux.The effects of gel bath temperature and evaporation time on membrane properties and structure were investigated.Optimizing the membrane process conditions.The experimental results showed that with the increase of gel bath temperature,the number of finger-shaped pores in the cross-section decreased,the penetrability decreased,and the pure water flux decreased.With the prolongation of evaporation time,the pore size decreased,and the pure water flux decreased.Through experimental analysis,the optimal preparation parameters of PES base membranes were obtained:PES content was 15 wt%,TMA content was 2 wt%,and gel bath temperature was 25°C.Under the preparation conditions,Amplify the PES ultrafiltration membrane for the pilot test.The pure water flux was 430 L·m-2·h-1.The BSA rejection rate was 97.82%.Using coating cross-linking method,Different concentrations of polyvinyl alcohol?PVA?aqueous solution were coated on the membrane surface,and subjected to high temperature treatment to obtain a low molecular weight cut off PES ultrafiltration membrane.In order to investigate the effect of PVA concentration and heat treatment temperature on the modified membrane properties,the PES membranes were tested under different conditions.With the increase of PVA concentration,the membrane pure water flux first rises and then decreases,the molecular weight cut off decreases first and then increases;as the heat treatment temperature increases,the membrane water flux decreases and the molecular weight cutoff decreases.When the PVA concentration was 0.1wt%and heat-treated was 80?,the minimum molecular weight of interception can reach 1000 g/mol.It was confirmed by infrared spectroscopy that PVA reacted with TMA to form a crosslinked structure.In the actual treatment of domestic wastewater,with the increase of wastewater concentration,the interception performance of the membrane increased,and finally reached a certain stable value.The permeation flux of the modified membrane increased after cleaning,which preliminarily indicated that PES ultrafiltration membrane had a certain anti-fouling property. |
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