Selectivity of anion exchange membrane modified with polyethyleneimine

Abstract

Previous works have been made on the improvement of selectivity of ion exchange membranes using adsorption of polyelectrolyte on the surface of the materials. The modification of the surface material in the case of an anion exchange membrane concerns the hydrophilic/hydrophobic balance properties and its relationship with the hydration state. Starting from this goal, the AMX membrane has been modified, in this work, by adsorption of polyethyleneimine on its surface. Many conditions of modification of the AMX membrane surface were studied. A factorial experimental design was used for determining the influent parameters on the AMX membrane modification. The results obtained have shown that the initial concentration of polyethyleneimine and the pH of solution were the main influent parameters on the adsorption of polyethyleneimine on the membrane surface. Competitive ion exchange reactions were studied for the modified and the unmodified membrane involving ${\text{C}}{{\text{l}}^{ - }}$, ${\text{NO}}_3^{ - }$ and ${\text{SO}}_4^{{2 - }}$ ions. All experiments were carried out at constant concentration of 0.3 mol L⁻¹ and at 25 °C. Ion exchange isotherms for the binary systems $\left( {{\text{C}}{{\text{l}}^{ - }}/{\text{NO}}_3^{ - }} \right)$, $\left( {{\text{C}}{{\text{l}}^{ - }}/{\text{SO}}_4^{{2 - }}} \right)$ and $\left( {{\text{NO}}_3^{ - }/{\text{SO}}_4^{{2 - }}} \right)$ were studied. The obtained results show that chloride was the most sorbed and the selectivity order both for the modified membrane and the unmodified one is: ${\text{Cl}} > {\text{NO}}_3^{ - } > {\text{SO}}_4^{{2 - }}$, under the experimental conditions. Selectivity coefficients ${\text{K}}_{{{\text{C}}{{\text{l}}^{ - }}}}^{{{\text{NO}}_3^{ - }}}$, ${\text{K}}_{{2{\text{C}}{{\text{l}}^{ - }}}}^{{{\text{SO}}_4^{{2 - }}}}$ and ${\text{K}}_{{2{\text{NO}}_3^{ - }}}^{{{\text{SO}}_4^{{2 - }}}}$ for the three binary systems and for the two membranes were determined. It was also observed that for the modified membrane the selectivity towards sulfate ion decrease and the modified membrane became more selective towards monovalent anions.