Preparation And Characteristics Of Composite Nanofiltration Membrane From Quaternized Chitosan

Chitosan is a kind of natural macromoleculer compounds,which have excellent biocompatibility,non-toxic and biodegradable characteristics,also often be used as membrane material.The quaternized chitosan is a kind of derivative of chitosan, which get through taking other groups or a low molecular quaternary ammonium salt into the amide groups of chitosan.It's more effective due to its more soluble than chitosan.First,the quaternized chitosan was preparated from chitosan;then the quaternized chitosan/ sulphonated polyether sulphone composite nanofiltration membrane was prepared by coating method;finally,a new kind of composite nanofiltration membrane was prepared by interfacial polymerization(IP) reaction occurred between the quaternized chitosan and trimesoyl chioride(TMC) onto a polyether sulphone ultrafiltration membrane.(1) The preparation of the quaternized chitosanChitosan was modified into 2-hydroxypropyltrimethyl ammonium chloride chitosan(HACC) with glycidyl trimethylammonium chloride(GTMAC),it is water soluble.The infrared spectrum shows that the H of the chitosan's amino-group was substituted partially by -CH₂CH(OH)CH₂N(CH₃)₃Cl,and the ratio of substitution is about 84%.(2) HACC/sulphonated polyether sulphone(SPES) composite nanofiltration membrane was prepared by coating methodThe HACC/SPES composite nanofiltration membrane was prepared by coating the solution of HACC onto SPES.The influences of prepared conditions,such as the concentrations of HACC,coating time,heat treatment temperature and time,on the performance of HACC/SPES membrane were systematically investigated.The optimized prepared condition of HACC/SPES membrane was as below:the basement membrane was immersed 36hours by concentrations of HACC(6%),then heated for 20min at 85℃.The experimental results showed that under the operating pressure of 0.4MPa,the pure water flux through the HACC/SPES membrane was 25.8 L·m^-2·h^-1, while the rejection to PEG1000 was 90.2%.The rejection to the four salts NaCl, MgCl₂,Na₂SO₄,MgSO₄ less than 10%.This membrane can be used in separating organics from small molecule and salt mixture solution.The results of scanning electron microscope(SEM) and atomic force microscope(AFM) showed that a compact selective layer was formed on the basement membrane by coating the solution of HACC.Due to the chemical reaction between the sulfonic acid groups of SPES and the HACC,crosslinking reagent wasn't used during preparation of the membrane,and the preparation process was simplified.The transmissivity of the electrolyte through the membrane was improved as the membrane contained anions and cations.a This preparation method of membrane has not been reported.(3) HACC/SPES composite nanofiltration membrane was prepared by interfacial polymerization(IP) reactionHACC/SPES composite nanofiltration membrane was prepared basing on the basement membrane-PES,HACC and TMC as the two monomers of IP reaction, hexane and water were choosen as solvents for TMC and HACC respectively.Various factors' influences on the performance of HACC/PES membrane,such as the concentrations of HACC and TMC in relevant solutions,heat treatment,were tested The IP reaction products between HACC and TMC were tested by infrared spectroscopy technology,the result showed that acylation reaction had taken place by -NH in HACC molecule and acid chloride group.The conditions were obtained as:HACC-0.3%(wt);TMC-0.3%(wt);the basement membrane being immersed in HACC solution for 30min,the IP reacting taking place for 2min.The water flux of the HACC/SPES membrane was 4.2L·m^-2·h^-1, while the rejection to PEG1000,Ethyl Green and other dyes was more than 90.0%. The rejection to the NaCl was about 30%.It can be concluded that the organic in molecular weight 1000 and salts of low molecular weight as NaCl can be separated efficiently by the membrane.The result showed that the membrane is a positively charged membrane,and can be used for the concentration of the positively charged materials.The results of SEM and AFM showed that a compact selective layer was formed on the basement membrane during IP reaction.The two different preparation methods of composite nanofiltration membrane used in the experiment has not been reported.This is the innovation of the research. The research results of the two kinds of nanofiltration membrane have established the foundation for further research.