Study On The Preparation Of Polyethersulfone Membrane By RTIPS Method And Its Filtration Performance For Different Process Water In Waterworks

At present,membrane separation technology is widely used in water treatment,medicine,biology,petroleum,environment,chemical industry,energy,metallurgy,textile,food,aerospace,electronics and other fields,bringing huge economic and social benefits to people,and has broad development and application prospects.In this study,polyethersulfone(PES)was used as the raw material for membrane preparation,N,N-dimethylacetamide(DMAc)as a polar solvent,polyethylene glycol(PEG)with different molecular weights(200,400 and 600)and diethylene glycol(DEG)as the non solvent to make PES flat membrane.Polyethersulfone flat membrane was maked by RTIPS,hollow fiber membrane and porous hollow fiber membrane were maked by coupling RTIPS with NIPS.The focus is on the regulation of the structure and performance of flat membranes and hollow fiber membranes by the membrane production process.The influence of membrane formation methods on the structure and performance of polyethersulfone flat membranes,single-pored hollow fiber membranes and porous hollow fiber membranes are emphatically explored.The prepared polyethersulfone membranes were investigated by using scanning electron microscopy(SEM),energy spectrum analysis(EDS),pure water flux,BSA interception,pure water contact angles,mechanical properties and application properties.This paper mainly studies from the following three aspects:Firstly,polyethersulfone(PES)was used as the raw material for membrane preparation,N,N-dimethylacetamide(DMAc)as a polar solvent,polyethylene glycol(PEG)with different molecular weights(200,400 and 600)and diethylene glycol(DEG)as the non solvent to prepare PES flat membrane.Four membrane-forming systems,PES/DMAc/DEG,PES/DMAc/PEG200,PES/DMAc/PEG400 and PES/DMAc/PEG600,were studied.The effects of PEG molecular weight and the mass ratio of nonsolvent to solvent on the phase separation temperature(cloud point)were analyzed.The effects of the film forming principle(RTIPS principle and NIPS principle)on the performance and structure of the polyethersulfone flat membrane under different gel bath temperatures was discussed.The experimental results show that the molecular weight of polyethersulfone has no influence on the change of the phase separation temperature of the casting liquid system.When the molecular weight of PEG increases,the cloud point of the casting solution increases.When the non-solvent/solvent mass ratio increases,the cloud point of the casting liquid decreases.When the gel bath temperature is lower than the cloud point,the film formation mechanism is the NIPS method,a dense skin layer is formed on the surface of the film,and there is a finger-like pore structure on the section of the film.When the gel bath temperature is higher than the cloud point of the casting solution,the film formation mechanism is controlled by the RTIPS process,uniform micropores are formed on the surface of the film,and bi-continuous structure is formed on the cross section of the film.The membrane prepared by the RTIPS method exhibits a higher pure water permeation flux than the membrane prepared by the NIPS method,and has better mechanical properties.MPEG200-4 and MDEG2 formulations,when the gel bath temperature is 80?,the permeability and mechanical properties of the membrane are the best.And the application results show that when grass sand raw water,flocculation tank effluent,sand filter effluent and ozone activated carbon effluent are used as membrane inlet water,the membrane effluent turbidity is stable,0.23±0.01 NTU,and the UV254 in the membrane inlet has a good removal effect.Secondly,PES hollow fiber membrane was prepared by using the PES flat membrane process parameters.Using the RTIPS-NIPS coupling method,the process parameters of the previously existing RTIPS method for preparing flat membranes were used to further optimize the spinning parameters of the polyethersulfone hollow fiber membrane,so as to obtain a polyethersulfone hollow fiber membrane with superior performance.Properties of hollow fiber were investigated by SEM,EDS,hollow fiber membrane's flux,rejection rate,cutting molecular weight and application performance.The experimental results show that the minimum flux of MPEG hollow fiber membrane is 222 L/(m~2·h),but the maximum BSA rejection rate is 80.36%.The maximum flux of MDEG hollow fiber membrane is 292 L/(m~2·h),while the rejection rate of BSA is 38.69%.The fluxes of the two sets of hollow fiber membranes prepared are close to those of the PES hollow fiber membranes produced commercially,and the interception effect is better.The application results show that the membrane effluent turbidity is stable at 0.20±0.01 NTU,and it has a good removal effect on the UV254 and TOC in the membrane influent.Finally,polyethersulfone(PES)as the membrane material,N,N-dimethylacetamide(DMAc)as a polar solvent,polyethylene glycol 200(PEG200)as the non-solvent.The structure and application properties of PES porous hollow fiber membrane were studied by using RTIPS-NIPS coupling method.The experimental results show that the flux of the prepared porous hollow fiber membrane is significantly greater than the single-pored hollow fiber membrane.There are micropores on the outer surface of the membrane,and the cross section is finger hole and sponge structure coexist.The application results show that the membrane effluent turbidity is stable at 0.21±0.01 NTU and UV254 in the influent was removed effectively.The long-term flux stability of the membrane shows that with the extension of the test time,the flux of the membrane wire will decrease significantly.When running for 40 hours,the flux decay rate of the membrane is only 60.98%.