Separation of ethylene glycol and alkali metal salts on carbon nanotubes and mosaic membranes

A method for separation of ethylene glycol (EG) and alkali metal salts in aqueous solutions is developed using solid-phase extraction on carbon nanotubes (CNT) and dialysis with a domestic mosaic membrane AK-45. Both methods enable effective separation of the components of EG + NaCl (KCl) aqueous solution which is necessary for gas chromatographic determination of EG in the mixtures. Hydrophobic-hydrophilic interactions in the EG – water – CNT system provide efficient sorption of EG and almost zero sorption of potassium chloride by CNT. Coefficients of EG and KCl separation on Dealtom carbon nanotubes range within 7 – 15 (for 0.001 ≤ C_{0 EG} ≤ 0.1, 0.001 ≤ C_{0 KCl} ≤ 0.1 mol/liter), EG extraction rate is 86 – 94% for single extraction. CNT practically do not absorb potassium chloride. High and low permeability of mosaic membranes for metal salts EG, respectively, is a basis for separation of EG and alkali metal salts by dialysis. During a 4-hour dialysis, 96% and 87% of NaCl (C₀ = 0.001 mol/dm³ and C₀ = 0.01 mol/dm³, respectively), are transferred as NaCl through the AK-45 membrane (86% and 82% for KCl). At the same time an amount of less than 3% EG (C₀ = 0 mol/dm³) is transferred during dialysis through AK-45 membrane. Mosaic membrane AK-45 appeared to be the most effective one regarding the transfer of alkali metal salts from low-mineralized aqueous solutions, unlike traditional ion-exchange membranes in the absebce of such transfer due to the Donnan phenomenon. Coefficients of alkali metal chloride and EG separation by dialysis with an AK-45 membrane range within 13 – 38, which indicates to their rather efficient separation.

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