Chromatographic Design Of Crown Ether Grafted Polysulfone Membrane And Lithium Isotope Separation Effect

Natural lithium consists of two isotopes(6Li 7.5%and 7Li 92.5%),which play an important role in the development of nuclear fusion.Enriched 6Li functions as a tritium breeder,as well as huge energy so as to impel tritium to continue proliferation in the fusion reactor.On the other hand,7Li is commonly used as a pH controller and coolant of the nuclear fusion reactor.Therefore,lithium isotope separation is of great important for the development and application of green nuclear energy.The aim of the present study is to prepare crown ether grafted chloromethylated polysulfone membranes and design membrane chromatography so as to efficiently separate lithium isotopes by elution chromatography method.According to the basic principle of membrane chromatography technology,4-aminobenzo-15-crown-5(AB15C5)as the membrane ligand and chloromethylated polysulfone as bulk polymer were used to prepare PSf-g-AB15C5 polymer via nucleophilic substitution,which was employed to fabricate PSf-g-AB15C5 porous membrane by nonsolvent induced phase inversion(NIPS)method.The porous membranes as media were filled to fabricate a chromatography column with 75 mm in height and 24 mm in diameter in 20 layers for lithium isotopic adsorptive separation.The result showed that 3.1 of the maximum theoretical plate number of the membrane chromatography column and 5.402 cm of the maximum half-peak width were obtained under the conditions of the amount of lithium salt(LiI)0.3 mg and the flow rate 0.3 mL/min.Further,the abundance of 7Li was increased by 0.06%.Moreover,the heavier isotope(7Li)was enriched in the front end of lithium adsorption bands in the chromatograpHic columns,while the 6Li was enriched in the back-end of bands.The single separation factor of the lithium isotope obtained from the membrane column was up to 1.01429.The three-stage membrane chromatography system was designed and carried out to enhance the performance of the three-stage membrane chromatography columns.The abundance of 7Li and 6Li was increased by 0.13%and 0.12%with the increase of elution stages,respectively.Particularly,to further increase the amount of Lil to 10 mg,the abundance of 7Li and 6Li obtained from five-stage elution membrane chromatography was increased by 0.19%and 0.17%,respectively.Finally,the membrane chromatography column with different membrane layers was conducted to investigate the effect of membrane layer on the performance of the column.The single separation factor of the lithium isotope obtained from the membrane column was up to 1.02098.The result showed the amount of lithium salt adsorption increased from 0.43 mg/g to 0.78 mg/g with an decrease of eluent temperature from 25 ℃ to 5 ℃.It was also found that the Freundlich isotherm model was more suitable to the adsorption process of lithium ions on PSf-g-AB15C5.The adsorption of lithium ions into PSf-g-AB15C5 microporous membrane was found to follow pseudo-seconder-order kinetic model well.It indicated that lithium ions were adsorbed by PSf-g-AB15C5 microporous membrane through the chemisorption.The maximum adsorption capacity was up to 13.11 mg/g.