Preparation Of PVDF/PSA Acid-resistant Composite Nanofiltration Membrane By Interfacial Polymerization And Study On Its Properties

Nanofiltration(NF)technology is a new type of pressure-driven membrane process developed to meet the needs of industrial softened water and reduce costs.Compared with the early asymmetrical NF membranes,composite NF membranes have the advantages of strong pressure and tightness,good selective separation performance,and good permeability,so they are widely used.At present,industrial waste liquids contain strong acids,while traditional separation membranes have poor acid resistance.Besides,some polymer materials with good acid stability are seldom used because of poor membrane formation and separation performance.Therefore,in this work,polyvinylidene fluoride(PVDF)ultrafiltration membrane with good mechanical properties,excellent chemical resistance and thermal stability was used as the supporting layer,on which a polysulfonamide(PSA)functional layer was constructed on the surface by interfacial polymerization,to obtain a composite NF membrane with good separation performance and excellent acid resistance.(1)The PVDF-g-AA/PSA composite NF membrane was prepared by a two-step method.The optimal preparation conditions of PVDF/PSA composite nanofiltration membrane are determined by membrane permeability and contact angle.The permeability and water contact angle of PVDF/PEI30 composite nanofiltration membrane are 19.8 L?m^-2?h^-1?bar^-1 and 62.5?,respectively.The permeability and water contact angle of the PVDF/CYS45 composite NF membrane are 25.2 L?m^-2?h^-1?bar^-1and 61.8?,respectively.Both of them have higher rejection rates for typical divalent inorganic salts(Mg SO₄,Na₂SO₄),among which the rejection rates of PVDF/PEI30 and PVDF/CYS45 membranes are 83.4%,85.6%and 90.1%,92.2%respectively.At the same time,the two types of modified membranes can achieve a rejection rate close to100%for the dye reactive red 2,showing good desalination and de-dyeing performance.Through static acid immersion and dynamic acid separation experiments,the contact angle of the modified membranes changed little before and after the treatment.In addition,the retention rate of the PVDF/PEI30 membrane for Mg SO₄ and Na₂SO₄ is above 70%,while the rejection rate of PVDF/CYS45 composite membrane is still as high as 80%or more.Furthermore,the rejection rate of the two composite NF membranes for Reactive Red 2 is close to 100%,showing excellent acid stability.(2)One-step preparation of PVDF/PSA ultra-thin acid-resistant composite NF membrane.Under the optimal preparation conditions of the composite NF membrane,the permeability of PVDF-g-AP/BDC is as high as 40.1 L?m^-2?h^-1?bar^-1,showing excellent permeability;the rejection rates for typical bivalent inorganic salt,Mg SO₄and Na₂SO₄,reach 90.1%and 91.1%,respectively,and the retention rate for the dye reactive red 2 is close to 100%,showing good desalting and de-dyeing performance.After static immersion and dynamic acid separation tests,the retention and separation performance of inorganic salts(Na₂SO₄,Mg SO₄)and dyes(reactive red 2)is almost unaffected by acid treatment,and the retention rate for both inorganic salts can be maintained at 84%Above,the dye removal rate is still close to 100%.Chemical structure and surface morphology tests such as infrared spectroscopy,scanning electron microscopy and atomic force microscopy confirm that the sulfonamide bonds on the membrane surface of the PVDF-g-AP/BDC composite NF membrane have not been significantly degraded,showing excellent acid stability.