Preparation Of Polyamide Nanofiltration Membrane Containing Nano-silver And Its Application In Separating Enzymatic Hydrolysate Of Chitosan

As a new type of separation technology,membrane separation technology has been developed rapidly and used widely in water treatment,gas separation,concentration extraction and other fields.However,the membrane surface is easy to be adsorbed by microorganisms thus causing microbial contamination,thereby reducing the membrane separation performance and service life.In order to solve the problem of membrane microbial contamination and improve the antibacterial ability of nanofiltration membrane,nano silver was loaded on the membrane surface,the composite nanofiltration membrane was prepared by interfacial polymerization method,and the prepared nanofiltration membrane was used to separate enzymatic hydrolysate of chitosan.The results of the study are as follows:1.Preparation of SPES polyamide nanofiltration membrane containing nano-silver.Sulfonated polyethersulfone(SPES)was prepared by sulfonating polyethersulfone(PES)with sulfuric acid as sulfonating agent,and SPES ultrafiltration membrane was prepared with SPES as material.The SPES-Ag ultrafiltration membrane was prepared by loading the nano-silver on the SPES ultrafiltration membrane throμgh sulfonic acid group and Ag+ coordination and Vc reduction ability.Then Trimesoyl chloride(TMC)and m-Phenylenediamine(PDA)were used as the oil phase monomer and the aqueous phase monomer respectively,the SPES-Ag/PA nanofiltration membrane was prepared by the interface polymerization method using SPES-Ag ultrafiltration membrane as the base membrane.When the sulfonation degree of SPES was 0.268,the water flux of SPES ultrafiltration membrane was 477.2 L.m-2.h-1,and the retention of BSA was 95.1%.The antibacterial activity of SPES-Ag ultrafiltration membrane was 97.7%,98.3% and 95.7%,against Escherichia coli,Pseudomonas and Staphylococcus aureus respectively.The antimicrobial activity of the SPES-Ag/PA nanofiltration membrane was 86.7%,90.3% and 87.7%,respectively,but the antibacterial activity became longer(from 30 days to 150 days),and the retention of MgCl2,MgSO4 reached 80%.2.Preparation of PES/SPES/SPEEK polyamide nanofiltration membranecontaining nano-silver Firstly PES/SPES ultrafiltration membranes with different PES/SPES ratios were prepared,then PES/SPES/SPEEK ultrafiltration membranes were preparedby adding different mass fraction of sulfonated poly(ether-ether-ketone)(SPEEK).PES/SPES/SPEEK was used as the base membrane to load the nano silver,and PES/SPES/SPEEK-Ag/PA nanofiltration membrane was prepared by interfacial polymerization.When PES/SPES was 50/50,the water contact angle of PES/SPES membrane was reduced by 25.4% and water flux increased by 46.6% compared with PES membrane.The addition of SPEEK can improve the hydrophilicity,mechanical and surface structure properties of the membrane.When the addition amount of SPEEK is 4%,the tensile strain of the membrane is increased by 161.7% and the maximum stress can reach 9.11 Mpa.Nanosilver which loaded on PES/SPES/SPEEK-Ag ultrafiltration membrane surface,is more uniform.The antibacterial activity of PES/SPES/SPEEK-Ag ultrafiltration membrane was 96.6%,96.3%,95.6%,against Escherichia coli,Pseudomonas and Staphylococcus aureus respectively.The antimicrobial activity of the PES/SPES/SPEEK-Ag/PA nanofiltration membrane was 87.7%,84.0%,80.0%.respectively.PA layer formed a network-like cross-linked structure and smaller pore size,improving the PES/SPES/SPEEK-Ag polyamide nanofiltration membrane retention performance,the retention of MgCl2,MgSO4 reached 86%.The nano-silver embedding effect is better,delayed the release rate of nano-silver,nanofiltration membrane antimicrobial durability increased to 170 days.3.Separation and purification of chitosan hydrolysis solution by PES/SPES/ SPEEK-Ag/PA nanofiltration membrane.Chitooligosaccharide mixture with a polymerization degree of 2~7 was obtained by controling the enzymolysis conditions as chitosan was digested by chitosanase.The PES/SPES/SPEEK-Ag/PA nanofiltration membrane was used to separate the chitosan hydrolyzate.The PES/SPES/SPEEK-Ag/PA nanofiltration membrane can pass through 1~3 sugar,has a good concentration effect for 5~6 sμgar,the yield of 4~6 sμgar is 23.54%.The nanofiltration showed a good anti-pollution ability,flux recovery rate of 90.4% by conventional cleaning.