Study On Preparation And Property Of Polyethersulfone Nanofiltration Membrane

In this paper,the polyethersulfone nanofiltration membrane was prepared by the immersion phase transformation with polyethersulfone as membrane making material,N,N'-dimethylacetamide as solvent and polyvinylpyrrolidone as porogen.The optimum separation performance of polyethersulfone nanofiltration membrane was chose through the separation of sodium selenate.The PES membrane was encapsulated as a membrane module of 1812 type.Then the separation performances of the self-made PES membrane and a commercial polysulfone NF membrane(1812-57N)were compared for separation of sodium selenite,selenium-methionine and their mixed aqueous solutions.For the two membranes,water contact angle,surface Zeta potential and rejection of MgSO4 were measured.The experiment focused on the effect of operation pressure on flux and rejection of the two types of membranes.The experimental result showed that the polyethersulfone nano filtration membrane with the best separation performance for sodium selenate could be prepared when the membrane thickness was 150 ?m,the porogen was PVP K30,and the solvent evaporation time was 5 s.The water contact angle value of the polyethersulfone membrane was smaller than that of the commercial nanofiltration membrane,indicating that the polyethersulfone membrane had better hydrophilicity.The Zeta potential value of the polyethersulfone membrane was smaller than that of the commercial nanofiltration membrane,indicating that the surface charge density of the polyethersulfone membrane was higher than that of the commercial nano filtration membrane.Under the optimal operating pressure,the polyethersulfone nanofiltration membrane had a high rejection effect on sodium selenate solution,which was higher than the rejection of sodium selenate by commercial nanofiltration membrane.At the same time,two types of nanofiltration membranes had almost no effect on selenium methionine.Polyethersulfone nanofiltration membrane can effectively reject sodium selenate and retain selenomethionine.At the same operating pressure,the flux of polyethersulfone membrane was more than twice that of commercial nanofiltration membrane.For the mixed solution,the rejection of sodium selenate by the polyethersulfone membrane was higher than that of the commercial nanofiltration membrane,while the rejection of selenomethionine was lower than that of the commercial nanofiltration membrane.Therefore,the polyethersulfone nano filtration membrane prepared in this experiment was more suitable for removing sodium selenate in aqueous solution and retaining selenomethionine.In this paper,UV-grafting modification was also studied on the basis of the prepared polyethersulfone nanofiltration membrane.In the experiment,N,N'-methylenebisacrylamide was used as a grafting monomer and Ce(?) was used as an initiator.UV-grafting modification was carried out under the irradiation of ultraviolet light.This experiment focused on the effect of monomer concentration on the modification effect.The five simulated dye solutions were separated by the modified nanofiltration membrane.The separation performance was compared with the performance of the nanofiltration membrane which was made by the others.An equation containing spectral color,charge and cutoff molecular weight was built to calculate the theoretical rejection of the different modified membranes.The experimental result showed that the UV-grafting reaction using Ce(?)as initiator and N,N'-methylenebisacrylamide as the monomer occured mainly on the surface of polyethersulfone nanofiltration membrane.The surface of the modified nanofiltration membrane was more smooth than the unmodified nanofiltration membrane.The water contact angle value of the modified nanofiltration membrane was smaller than that of the unmodified nano filtration membrane,which indicated that the modification increased the hydrophilicity of the nanofiltration membrane.In the nanofiltration membrane modification process,with the increase of monomer concentration,the Zeta potential first decreased and then increased.This indicated that with the increase of monomer concentration,the surface charge density of the modified nanofiltration membrane increased firstly and then decreased.When the monomer concentration was 6 mmol/L,the initiator concentration was 0.04 mol/L,and the modified time was 7 min,the modified nanofiltration membrane had the best separation performance for the five simulated dye solution.Except for methylene blue,the changing trend of rejection versus BIS concentration between the theoretical and experimental values was same.For rhodamine B,acid fuchsin and acid chrome blue K,the theoretical rejection was similar to the experimental rejection.