Preparation of ionic polyimide polymer membrane and separation performance of magnesium and lithium
In order to meet the increasing demand for lithium resources,diaminodibenzo-14-crown-4(DAB14C4),2-(3,5-diaminophenyl)-benzimidazole(DABI)and 4,4-hexafluoroisopropyl phthalic anhydride(6FDA)were used.A novel polyimide polymer was prepared by polycondensation,quaternization and ion exchange reaction.Polymer porous membranes were prepared by NIPS method,and ion diffusion experiments were carried out.The results showed that crown ether-imidazole-based ionic polyimide polymer(PI-C-IL-NTf2)was successfully synthesized.The crown ether immobilization amount of PI-C-IL-NTf2 was 0.97 mmol/g,the imidazole immobilization amount was 0.51 mmol/g,NTf2-anion substitution degree was 72％,molecular weight was 30 000,and glass transition temperature was 170.1 ℃.The prepared polymer porous membrane structure was dense in the upper layer,and the support layer was a through-hole structure that penetrates evenly;the average pore size was(8.95±0.4)nm,the porosity was(74.8±0.7)％,the mechanical strength was 5.2 MPa,the pure water contact angle was 71.2°,and the pure water permeability was 285 L/(m2·h·MPa).The permeation rates of porous membrane for Li and Mg2+were 0.258 μm/s and 0.0455 μm/s respectively,and the Li/Mg separation factor was 9.49.
crown etherbenzimidazolepolyimideselective separation of magnesium and lithium
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