Preparation Of Crown Ether-functionalized Nanofiltration Membrane And Study On Its Lithium-magnesium Separation Performance

The rapid development of the world leads to the steady and rapid growth of the demand for lithium resources in many industries,resulting in a large demand for lithium resources gap.The global lithium resources mainly exist in salt lake brines with high magnesium lithium mass ratio.Therefore,it is of great significance to separate lithium magnesium from salt lake brines for the extraction of lithium resources.Based on the high selectivity of crown ether to lithium and the high efficiency of nanofiltration membrane to lithium magnesium,crown ether functionalized nanofiltration membrane was first prepared for the separation of lithium magnesium.The main research contents and results are as follows:(1)Diaminodibenzo-14-crown-4(DAB14C4)was prepared.First,dibenzo-14-canopy-4(DB14C4)was prepared by template method,then dinitrodibenzo-14-canopy-4(DNB14C4)was prepared by nitration reaction,and finally,diaminodibenzo-14-canopy-4(DAB14C4)was prepared by palladium carbon reduction.The intermediates and products were characterized by IR and NMR.The results showed that DAB14C4was successfully prepared.(2)Crown ether functionalized nanofiltration membranes were prepared by interfacial polymerization.Using infrared spectroscopy(FTIR)and XPS to characterize surface chemical structure of the crown ether functionalized nanofiltration membrane,using Zeta potentiometer to characterize the charge of the crown ether functionalized nanofiltration membrane surface,thus explores the formation process of the crown ether functionalized nanofiltration membrane.The performance of crown ether functionalized nanofiltration membranes were characterized by permeance and salt rejection,and the preparation of crown ether functionalized nanofiltration membranes was optimized.DAB14C4 solvent,0.1%DAB14C4,0.5%triethylamine,0.5%TMC,2min reaction time and 50?hot water treatment temperature were selected to prepare crown ether functionalized nanofiltration membrane.The permeance of crown ether functionalized nanofiltration membrane was 13L·m^-2·h^-1·bar^-1,and the rejection of Na₂SO₄was 65%.(3)The separation performance of lithium magnesium in crown ether functionalized nanofiltration membrane were investigated.Experiments on the separation of lithium and magnesium on the crown ether functionalized nanofiltration membrane show that the mass ratio of magnesium to lithium has a greater impact on the separation of lithium and magnesium on the crown ether functionalized nanofiltration membrane.The operating pressure,solution p H,and operating temperature have a relatively small impact on the separation of lithium and magnesium on the crown ether functionalized nanofiltration membrane.The separation factor S_Mg,Liof crown ether functionalized nanofiltration membrane is 3.6,permeance is 13 L·m^-2·h^-1·bar^-1.Compared with nanofiltration membranes reported in the literature and commercial nanofiltration membranes,crown ether functionalized nanofiltration membrane has excellent membrane performance due to higher separation factor of magnesium and lithium and higher permeance.