Preparation Of Sulfonate-type Copoly(Phthalazinone Biphenyl Ether Sulfone)Composite Nanofiltration Membrane

As a type of separation process driven by pressure without phase change,nanofiltration technology is mainly used for the separation of monovalent and multivalent ions and the interception of small organic molecules with molecular weight cut-off（MWCO）between 200-2000 Da.The core of nanofiltration technology is the nanofiltration membrane.The membrane material determines the performance of the nanofiltration membrane.As its excellent thermal,chemical stability and solubility,the copoly（phthalazinone biphenyl ether sulfone）（PPBES）is a potential material in nanofiltration membranes.However,the water flux of nanofiltration membrane prepared by PPBES still need to be advanced,so in this paper,sulfonic acid groups were introduced into PPBES,and the monovalent counter ions（Li,Na and K）with different radii were used to replace the sulfonic acid hydrogen,leading relatively loose separation layer,which can further increased the permeation flux of the membranes.Using copoly（phthalazinone biphenyl ether sulfone）（PPBES）as raw material,homogeneous sulfonation was used to obtain sulfonated copoly（phthalazinone biphenyl ether sulfone）（SPPBES）.The effect of reaction time and temperature on the degree of sulfonation of the polymer was systematically studied.The SPPBES was immersed in salt solutions to obtain the sulfonate type sulfonated copoly（phthalazinone biphenyl ether sulfone）（SPPBES-M）,and the structure and properties of the polymer were characterized.The ¹H-NMR spectrum and the infrared spectrum confirmed the synthesis of the sulfonated polymer and that the counter ion was introduced.The kinds of counter ions in SPPBES-M were detected through ICPMS,and titration confirmed that 100%hydrogen ions on sulfonate group were substituted by alkali metal ions.SPPBES has two thermal weight loss platforms.The initial thermal decomposition temperature of SPPBES-M is higher than 460℃,so that it has excellent thermal stability;It has good solubility.With SPPBES-M as the coating material and PPBES ultrafiltration membrane as the bottom membrane,the SPPBES-X-M/PPBES composite nanofiltration membrane was prepared by the coating method,and the influence of the sulfonation degree,SPPBES-M concentration,counter ion species,heat treatment conditions and operating conditions on the performance of composite nanofiltration membranes are studied.Taking SPPBES-X-K as an example,as different sulfonation of SPPBES-M increased,the permeation flux of the composite nanofiltration membrane gradually increased,and the salt rejection rate decreased.Taking SPPBES-100-K as an example,as the mass fraction of SPPBES-100-K in the dipping solution increased,the water flux of SPPBES-100-K/PPBES gradually decreased,and the salt rejection rate gradually increased.As the counter ions radius gradually increase in the sequence of Li,Na and K,the water flux of the composite nanofiltration membrane increased,and the salt rejection rate decreased.The water contact angle,characterizes the hydrophilic properties of the SPPBES-100-M/PPBES nanofiltration membrane,decreased to 50.6°,which means the hydrophilicity was enhanced.As the heat treatment temperature increased from 70℃to 100℃,the flux of SPPBES-100-K/PPBES composite nanofiltration membrane is reduced from 34.0L·m^-2·h^-1 to 21.4 L·m^-2·h^-1,and the salt rejection rate is increased from 69%to 75%;as the heat treatment time prolonged,the flux and salt rejection rate of the composite nanofiltration membrane show the same changing trend as the temperature rises.Changing the operating temperature of the SPPBES-X-K/PPBES composite nanofiltration membrane by first rises and then drops back to the initial temperature,the performance of the composite nanofiltration membrane does not change before and after the test;with the increase of operating pressure,the water flux shows an upward trend,and the salt rejection rate is basically unchanged;with the extension of the operating time,the water flux showed a certain change,and the salt rejection rate remained unchanged.The composite nanofiltration membrane has excellent chemical stability;After treated by acid and base,the water flux increased,and the salt rejection rate remained unchanged.