Design And Preparation Of Crown Ether-supported Microspheres For Lithium Separation

Crown ethers are a class of polyether compounds containing repeating -CH2-O-CH2-structures. They having strong coordination ability and highly selective to metal ions. Crown ethers have been used for lithium extraction in practical process due to their selectivity. Whereas, the coordination ability of varied crown ethers for lithium ions can be influenced by various factors, such as its cavity size, substituent groups, type and amount of donor atoms, etc. It is very necessary to study the interaction between crown ethers and Lithium irons because of the tedious and lengthy exploration of experiments. At present the main theoretical studies have focused on the 15-crown-5,18-crown-6 and 12-crown-4, etc., but the experiments concentrated on benzo crown ether series. In this study, model crown ethers with different cavity, donor atoms, and electron donating/withdrawing substituent groups were designed properly and used carefully to access the chemical structures and thermodynamic parameters of Li-crown ethers complexes by density functional theory (DFT) at B3LYP/6-311+G(d,p) level. It turned out that benzo-15-crown-5 has the better metal coordination ability than other benzo-crown ethers. The different electron withdrawing and electron donating functional groups on the benzene ring can influence the electron density then change the charge of donor atoms. The coordination ability of aza benzo-15-crown-5 is closed to the oxa benzo-15-crown-5, but the coordination ability of thia benzo-15-crown-5 is bad. So the coordination ability of crown ethers can be improve by change the ring size, the electron donating functional groups etc. It is expected that these results are of great significance for lithium separation in the practical application of crown ethers.It reduce the toxicity and drain of crown ethers overtly to immobilize the crown ethers to the surface of certain materials. In order to meet the requirements of industrial lithium isotope separation, these materials must be durable with enough high isotope separation properties. In this paper some activated crown ether was synthesized, such as amino benzo-15-crown-5, acetyl benzo-15-crown-5, amino benzo-18-crown-6 etc. Then we synthesis the GMA-PVDF micro sphere through pre-irradiation grafting. The amino benzo-15-crown-5 was immobilized to the GMA-PVDF micro sphere through the reaction between amino and epoxy groups. The crown ethers mass-content in the crown ether resin PG-B15 is 1mmol/g. All products were verified by FT-IR, NMR, TG, SEM and XPS. It turned out that the equilibrium time is 20 hours for the lithium adsorption of PG-B5 in aqueous solution. The capacity is 4.5 mgLi/g. And the separation coefficient is 1.022. The anion and solvent in separation is important. The Lithium thiocyanate and lithium iodide show high adsorption capacity and separation coefficient. The Lithium adsorption capacity and separation coefficient is high in THF and low in ethanol and acetone.