Structural analysis and defect evaluation of ion exchange composite membranes used in electrolysis of sodium chloride in chlor-alkali process

Abstract

Various tests were conducted to characterize a used ion exchange membrane. The DSC tests provided information on the water absorption capacity and phase transition of the used and fresh membranes. Also, information on the temperature of chemical degradation was obtained by the DSC tests. The DSC test was performed to analyze thermo-physical processes during the increase in temperature. The SEM images were used for the structural analysis of a Nafion composite membrane. The SEM images were taken from the used and fresh membranes. The layers are nearly similar in both the membranes (fresh and used), but the mineral-coated layer is deteriorated and engraved in the used membrane, particularly on the PTFE network fiber. EDX tests were conducted for the elemental analysis of the fresh and used membranes. The EDX analysis indicated the presence of Zr, Ti and O, which could be attributed to ZrO2 and TiO2 on a top layer. At the cathode side of the membranes, one cannot see the mineral layer. The population of S atoms was less in bulk polymer. The fresh membrane consists of F and C, while the used membrane shows new peaks of Ba, Ca, Mg and Si atoms, indicating the presence of inorganic materials in the bulk of the used membrane. This can be ascribed to the impurities present in brine, which is introduced to the membrane during cell operation. FTIR analysis showed that there were no chemical changes in the used membranes, due to its perfect chemical stability in a harsh environment. The results showed significant changes in the mineral composition of the used membrane after operation in a chlor-alkali cell.