Lithium Isotope Separation Performance Of Monoazabenzo-15-crown-5 Grafted Polysulfone Membrane

Lithium resources are very rich in the earth.Natural lithium consists of two stable isotopes 6Li and 7Li with approximately 7.5%and 92.5%,respectively.In nuclear fusion,6Li is used to be bombarded by neutrons to generate tritium and helium,as well as huge energy so as to impel tritium to continue proliferation in the fusion reactor.Moreover,7Li could be used as coolant of nuclear fusion reactor heap heart,the heat-carrying agent of heat conduction and thorium reactor molten salt media.Therefore,lithium isotope separation is of great importance during the development and application of nuclear energy.It is related to the implementation of national energy security and sustainable development strategy.A novel polysulfone(PSf)-graft-monoaza benzo-15-crown-5-ethers(BN15C5)(PSF-g-BN15C5)membrane was prepared from polysulfone and monoaza benzo-15-crown-5-ethers(BN15C5)via nucleophilic substitution reaction.The lithium isotope separation performance of membrane was investigated in this study.Chloromethylated polysulfone(CMPSF)with 0.4 degree of substitution and monoaza benzo-15-crown-5-ethers(BN15C5)were prepared.BN15C5 grafted polysulfone(PSF-g-BN15C5)polymer material was synthetised through the unimolecular nucleophilic substitution reaction(SN1)between the chloromethyl groups of CMPSF and the amino groups of BN15C5.The chemical composition and structure of the CMPSF,BN15C5 and PSF-g-BN15C5 polymer were characterized by nuclear magnetic resonance spectrometer(1H-NMR),fourier transform infrared(FT-IR),X-ray photoelectron spectroscopy(XPS)and thermogravimetric analysis(TGA).The results showed that the BN15C5 molecules were successfully grafted to polysulfone backbone.The PSF-g-BN15C5 polymer with 0.654meq.g-1 was obtained under the conditions:the mass ratio of BN15C5 and CMPSF 1.25:1,the polymer concentration 19.77%±0.5%,the reaction time 7.12 ± 0.1 h,the reaction temperature 71.64±0.6℃.The microstructures of PSF-g-BN15C5 polymer were prepared by phase inversion method.The effects of casting liquid content,coagulation bath type,casting solution temperature and additive dosage on the structure and properties of microporous membrane were investigated.With the increase of the temperature of the casting solution,the liquid content of the casting film increases,the change of the coagulation bath and the use of the additive.The microporous membrane finger hole is gradually eliminated and the complete sponge hole appears.The flux decreases with the increase of the liquid content of the cast film and the non-solvent diffusion rate increases with the increase of the temperature of the coagulation bath,and the pure water flux increases.PSF-g-BN15C5 microporous membrane was prepared by PSF-g-BN15C5 polymer solution as casting solution and phase inversion method.The single stage separation factor increased from 1.009 ± 0.001 to 1.049 ± 0.002 with the increase of the immobilization amount of crown ether from 0.23 to 0.58 meq.g-1 on PSF-g-BN15C5 microporous membrane in the solid-liquid extraction system of H2O-LiI/PSF-g-BN15C5.Furthermore,6Li was enriched in membrane phase and 7Li was enriched in the the solution phase.