Design And Preparation Of The Acid-resistant Nanofiltration Membrane With Triazine Ring Structure

Nanofiltration technology with low operating prssure and excellent capabilities to separate divalent metallic ions from monovalent ions has been widely used in water treatment.So far,most of the commercially avaliable nanofiltration membranes are polyamide(PA)composite membrane made from interfacial polymerization of polyfunctional acyl chloride and polyfunctional amines.However,amide linkages in PA are susceptible to nucleophilic attack and PA membrane cannot tolerate continuous exposure to low pH conditons.Consequently,PA membrane are excluded in many industrial applications.Cyanuric chloride(CC)is a reactive compond and polymers synthesized from nucleophilic substitution reaction of CC and various nucleophiles always have better chemical resistance and thermal resistance.Acid resistant membrane was expectable when CC was used as organic monomer to interfacial polymerized with nucleophilic monomers.Nevertheless,the reactivity of CC is step-wise decreased with the progress of nucleophilic substitution reaction and it is difficult to obtain well-defined polymer membranes through conventional interfacial polymerization of CC and nucleophiles.Strategies including synthesizing composite membrane with s-triazine amine structure and choosing nucleophiles with weak electronegativity were adopted in this doctoral dissertation to reach the goal of farbricating acid resistant membranes based on CC compound.High performance acid resistant poly(amide-s-triazine-amine)compoiste membrane and poly(s-triazine)arylether composite membrane made from cyanuric chloride and aromatic nucleophiles through direct interfacial polymerization were sucessfully obtained.Furthermore,rigid contorted monomer was introduced as aqueous monomer in interfacial polymerization with CC to fabricate an acid resistant poly(s-triazine)arylether composite membrane with higher solvent permeability.Main content of this dissertation includes the following three aspects:(1)Study on the acid resistant poly(amide-s-triazine-amine)compoiste membrane.As the reactivity of CC is step-wise decreased with the progress of nucleophilic substitution reaction,the precursor of poly(s-triazine-amine),1,3,5-(tri-piperazine)-triazine(TPT),was first synthesized through a functional-group protecting nucleophilic substitution reaction;then the precursor was used as aqueous monomer in the interfacial polymerization reaction with trimesoyl chloride(TMC)to fabricate NF membrane on the polysulfone(PSf)ultrafiltration(UF)membrane(TPT-TMC/PSf).The characterization results showed that TPT-TMC/PSf membrane has a well defined,compact and negatively charged skin layer with the isoelectric point around pH 3.5;TPT-TMC/PSf membrane exhibits good rejection to divalent salt solutions(Na2SO4(98.6%)>MgSO4(97.0%)>NaCl(40.5%))and the membrane water permeability was about 8.68 Lm-2bar-1.After exposure to 0.05 M H2SO4 for 720 h,TPT-TMC/PSf membrane still has a MgSO4 rejection above 94.2%and no evident chemical and morphological changes were observed in the skin layer of the membrane after the long term acid treatment.Comparing to the classical poly(piperazine)amide NF membrane,the incorporation of the s-triazine-amine structure into the polymer backbone can effectively enhance the acid stability of the poly(amide-s-triazine-amine)composite membrane.(2)Study on the acid resistant HQ-CC/PAN polyarylether composite membrane.As the reactivity of CC is step wise decreased with the progress of nucleophilic substitution reaction,and in order to avoid the extra cost increasd by the precursor preparation,hydroquinone(HQ)with weak electronegativity was adopted as the counter nucleophilic monomer in the in-situ interfacial polymerization reaction with CC based on the mechanism that the nuceophilic substituent with weak electronegativity deactive CC less.The characterization results showed that an original acid resistant poly(s-triazine)arylether composite membrane was successfully obtained through in-situ interfacial polymerization of CC and HQ on the porous polyacrylonitrile(PAN)UF membrane(HQ-CC/PAN).This well-defined composite membrane is a highly negatively charged NF membrane(pH?4.0)with rather smooth and thin morphology.The rigid structure of the monomers endow HQ-CC/PAN poly(s-triazine)arylether membrane with excellent separation performance.The rejection to Sunset Yellow solution was up to 96.0%with a water permeability of 12.0 Lm-2h-1bar-1.The presence of the chemical inert ether bond,benzene ring and s-triazine ring in the membrane backbone endow excellet acid stability to the composite membrane.After being immersed in the acidic solution for 28 days,the rejection to Sunset Yellow solution was still keep above 94.1%and no significant changes were observed in the chemical structure and morphology of the composite membrane.(3)Study on the high permeance acid resistant TTSBI-CC/PAN poly(s-triazine)arylether composite membrane.Based on the film-forming feasiblity between CC and polyphenol and in order to further increase the solvent permeance of acid resistant NF membrane,rigid contorted monomer 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane(TTSBI)was employed to interfacial polymerized with CC on the porous polyacrylonitrile(PAN)UF membrane.The spior-centre within TTSBI has an angle of 90°,and when reacts with CC the TTSBI units are held in non-coplanar orientation,enchancing the free volume of the polymer.The characterization results showed that TTSBI-CC/PAN poly(s-triazine)arylether composite membrane was successfully obtained through in-situ interfacial polymerization of CC and TTSBI on the porous polyacrylonitrile(PAN)UF membrane.This well-defined composite membrane is a highly negatively charged NF membrane with rather smooth and thin morphology.The crosslinking degree of TTSBI-CC/PAN membrane was higher than that of HQ-CC/PAN membrane and the selectivity to Sunset Yellow solution was up to 99.0%with a high water permeability of 21.0 Lm-2h-1bar-1.The high water permeability of the composite membrane is attribute to the presence of the rigid contorted monomer.After being immersed in the acidic solution for 28 days,the selectivity to Sunset Yellow solution was still retain as high as 96.5%and no significant changes were observed in the chemical structure and morphology of the poly(s-triazine)arylether composite membrane.In conclusion,this doctoral dissertation aimed at fabricating acid resistant NF membrane based on CC compound through interfacial polymerization process and NF membranes with various chemical structure was sucessfully designed and prepared through adopting different strategies.Original NF membranes possess both high performance and good acid resistance and can be used in the separation process of acid substances.The work in this dissertation provide new thoughts for the development of novel acid resistant membranes.