Preparation And Properties Of Reverse Osmosis And Nanofiltration Membrane Based On Novel Monomer

Nowadays,polyamide(PA)thin film composite(TFC)membrane prepared by interfacial polymerization has been the mainstream of reverse osmosis(RO)and nanofiltration(NF)membrane.Commercial PA membranes are fabricated by trimesoyl chloride(TMC)as an organic phase monomer.Though PA membranes prepared by TMC exhibit outstanding separation property,they still suffer from some drawbacks,such as the "trade-off" effect between water flux and salt rejection,membrane fouling and chlorination.In this thesis,we synthesized a series of organic phase monomers based on the drawbacks of PA membranes,and used them to prepare membranes with specific function according to the structure characteristic of these monomers.On the other hand,we developed a new method of surface modification for improving the antifouling property of PA membranes.1.PA TFC membranes for seawater desalination were prepared using isophthaloyl dichloride(IPC)and 3,3',5,5'-biphenyl tetraacyl chloride(BTEC)as organic phase comonomers to react with m-phenylenediamine(MPD).With the IPC weight percentage increasing from 0%to 70%,the water flux of the TFC membrane increased from 30 L/(m2h)to 43.7 L/(m2h)and the salt rejection increased from 99.3%to 99.7%under seawater desalination conditions.The characterization results indicate that the introduction of IPC not only increases the polyamide segment length between two crosslinking points which results in the enlargement of network of PA chain,but also enhances the reaction degree of acyl chloride groups on BTEC.The prepared membranes possesses high water flux and salt rejection.2.A novel diacyl chloride monomer with-PO(OCH3)2 group,dimethyl(3,5-bis(chlorocarbonyl)phenyl)phosphonate(I),was successfully synthesized by a Phosphorus-Carbon coupling reaction.PA TFC membranes functionalized by-PO(OCH3)2 were prepared using I and BTEC as organic phase comonomers to react with MPD.Through adjusting the adding content of I,the water flux of homemade membrane could reach 79 L/(m2h),which is 2.25 times higher than that of membrane prepared without I.Meanwhile,the salt rejection was above 99%.The testing results of membrane cotact angle and suface energy indicate that introducing-PO(OCH3)2 group results in the enhancement of membrane hydrophilicity.Then,the antifouling property of prepared membrane was measured.After 1500 minutes fouling,the irreversible fouling degree of homemade membrane was only half of that of commercial BW30FR,which demonstrates that the homemade membrane owns excellent antifouling property.3.A acyl chloride monomer with a-PO(Cl)2 group,5-(dichlorophosphoryl)isophthaloyl dichloride(5-DCPO-IPDC),was successfully synthesized.NF membranes were prepared using 5-DCPO-IPDC and BTEC as organic phase comonomers to react with MPD.When the concentration ratio of 5-DCPO-IPDC to the monomers in organic phase was 60%,the Na2SO4 and NaCl rejection of homemade membrane were 99.0%and 48.8%,and the pure water flux was 86 L/(m2h).Compared with the commercial NF270,the water flux of our membrane was1.45 times to that of NF270 under similar salt rejection.The testing results of XPS and zeta potentials illustrate amounts of phosphoric acid groups exist onto membrane surface which can enhance the amount of negative charges on active layer.Result from molecular weight cut off(MWCO)indicates the effect pore size of membranes produced with 5-DCPO-IPDC is larger and the active layer is looser compared with pristine membranes.This is because the tetrahedron structure of 5-DCPO-IPDC can prevent the close stack of polyamide chain.Larger pore size is benefit for the improvement of water flux,and more negative charges are in favor of guaranteeing salt rejection.An outstanding NF membrane is obtained under this synergistic effect.4.Sulfochlorinated polysulfone(SC-PSf)was synthesized through sulfochlorination of polysulfone(PSf).Then,the sulfonyl chloride groups on SC-PSf were partially hydrolyzed to sulfonic groups to produce sulfonated SC-PSf(SC-S-PSf).A chlorine-resistant RO membrane was fabricated by coating solution of SC-S-PSf on PSf substrate and then was crosslinked by piperazine(PIP).Tetrabutylammonium chloride(TBAC)as an addition was used to refrain from the defect on separation layer.Through optimizing preparation conditions,the NaCl rejection and water flux of homemade membrane could reach 96.9%and 1 7.8 L/(m2h).After immersing into 2000 ppm NaOCI for 10 days,the salt rejection of functional PSf membrane only decreased by 1%.In contrast,the salt rejection of PA membrane decreased by 8%under the same condition.The chlorine resistance of functional PSf membrane is excellent.5.A modified PA membrane of phosphonic acid group was fabricated by two simple steps.Firstly,a secondly interfacial reaction was implemented between ethylenediamine and the residual acryl chloride on the pristine PA layer,generating a surface enriched by primary amine.Secondly,utilizing the Mannich reaction between phosphorous acid,amine and formaldehyde produced a membrane surface modified by phosphonic acid groups.Separately optimizing the reaction conditions of the above two steps,the water flux of membranes enhanced from 52 L/(m2h)to 88 L/(m2h),and the salt rejection changes slightly.The contact angle decreased from 55° to 26°.Undergoing a dynamic fouling experiment for 800mins,the irreversible fouling degree of modified membrane was 7.1%,while that of commercial BW30 was 13.5%,demonstrating the modified membrane with outstanding antifouling property.