Preparation, Characterization And Properties Of Polyamide Composite Membranes Modified With Palygorskite

Drinking water security is an important prerequisite for promoting sustainable economic and social development and ensuring people's health.With the continuous improvementof urban residents'living standards,the main contradiction in the water supply industry began to change from insufficient water supply to drinking water quality.The traditional drinking water treatment process is often used to remove colloids,organics,bacteria and microorganisms in water,but it can not effectively limit the content of ions,disinfection byproducts and other pollutants in water.These pollutants generally have the characteristics of low dose,complex and small molecular weight.Nanofiltration has great advantages and potential in drinking water purification because of its unique separation performance and low production energy consumption.At present,how to increase the water flux of nanofiltration membrane and reduce the membrane surface pollution has become a research hotspot and difficulty.From the perspective of membrane material design and guided by the practical problems of NF membrane in the process of drinking water purification,polyamide composite nanofiltration membrane with good performance suitable for advanced drinking water treatment process is prepared in this thesis.The main research contents are as follows:Polyamide nanofiltration membrane was prepared by interfacial polycondensation(IP)with polysulfone(PSF)ultrafiltration membrane as substrate and piperazine(PIP)and homobenzoyl chloride(TMC)system.Through the detailed study on the preparation factors of nanofiltration membrane,the optimal preparation process is as follows:the addition amount of PIP is 0.3 wt%,the addition amount of TMC is 0.15 wt%,the aqueous phase immersion time is90 s,the IP reaction time is 40 s,and the post-treatment is 80?/5 min.The removal rate of Na₂SO₄ was 97.1%and the water flux was 55 L·m^-2·h^-1(room temperature 25?).The prepared nanofiltration membrane was characterized.It was found that the surface of the composite membrane showed an obvious nodular structure;The membrane surface is negatively charged,and the surface water contact angle is 46.7°.Nanofiltration membrane has good selective permeability.The sequence of salt cutting is Na₂SO₄>Mg SO₄>Na Cl,and the stability of nanofiltration membrane is good.Polyamide composite nanofiltration membrane modified by palygorskite(Pal)was prepared by blending.The surface modification of nanofiltration membrane(PA-NF membrane)prepared by the optimized process shows that pal particles can significantly affect the performance of nanofiltration membrane,and the best membrane performance is obtained when the addition amount of Pal particles is 0.01 wt%.Under the optimum preparation conditions,the water flux of the modified nanofiltration membrane was increased by 34%compared with that of the unmodified nanofiltration membrane,and the rejection rate did not decrease significantly.Through the characterization experiment,it is found that the surface of TFN-P_x film(modified film)is more rough than PA-NF film.When the addition amount of Pal nanoparticles is in the range of 0.005 wt%?0.01 wt%,the sphericalprotrusion and roughness of TFN-P_x film surface increase.The addition amount of Palnanoparticles was further increased to 0.03 wt%.Due to the agglomeration of Pal particles and the boundary void effect with the polymer,obvious pores were observed on the PA layer.The water contact angle and zeta potential of TFN-P_x membrane are lowerthan those of nanofiltration membrane,which proves that pal particles can significantly improve the hydrophilicity of the membrane;The surface of TFN-P_x film has strong negative charge,which provides a variety of possibilities for the application of the film.The exclusion order of the modified membrane to salt solution is consistent with that of PA-NF membrane,and the stability of the membrane is good,which proves that pal particles are firmly"embedded"in the separation layer.The anti fouling ability of the modified membrane was improved compared with that before modification,indicating that Pal particles can increase the anti fouling ability of the membrane.TFN-P_0.01 membrane(Pal addition of 0.01 wt%)has good purification performancefor drinking water.When the feed liquid is tap water,the inlet water temperature increases from25?to 55?,The water flux of TFN-P_0.01 membrane increased by 56%.TFN-P_0.01 The stability of membrane filtration for a long time is good.TFN-P_0.01 membranehas good removal efficiency of organic matter,UV₂₅₄ in effluent is less than 0.001cm^-1,and the average removal rate of COD_Mn is 70.3%;The removal rates of TDS,and hardness of drinking water were 62.4%and72.69%respectively;TFN-P_0.01 membrane can effectively remove divalent ions from water and retain monovalent ions,reflecting better selective separation performance;The p H value of drinking water decreased slightlyafter membrane filtration,and the water body was still alkaline.