Stability studies of poly(vinyl chloride)-based polymer inclusion membranes containing Aliquat 336 as a carrier

► Polymer inclusion membranes’ (PIMs) stability in aqueous solutions is studied. ► All PIMs are originally made of PVC and Aliquat 336 (R3MeN+Cl−). ► In some membranes the Cl− anion is replaced by NO3-, SCN−, ClO4-, Ac− and SO42-. ► PIMs lose (R3MeN+)nXn− to the aqueous phase to reach a stable composition. ► The loss is minimized or eliminated by increasing the aqueous concentration of Xn−. The stability of poly(vinyl chloride)-based polymer inclusion membranes (PIMs) containing 40%(w/w) Aliquat 336 (R3MeN+Cl−) and 60%(w/w) PVC is studied in detail when these membranes are immersed in deionized water and in aqueous solutions containing various salts or hydrochloric acid. It is shown that the mass loss is suppressed in the salt solutions and that the effectiveness of the suppression follows the order: NaClO4>NaNO3>NaSCN>NaCl≈LiCl≈HCl>Na2SO4>CH3COONa. It is also demonstrated that the distribution ratio of R3MeN+X− (where X− is Cl− or NO3-) between the PIM and the aqueous solution depends on the concentration of the “common anion” X− in the solution. However, in every case, the PIM eventually reaches an equilibrium with the aqueous solution, and after that the PIM composition remains stable. The ion-exchange equilibrium constants between Cl− on one hand and NO3- or SO42- on the other are reported to be Kie-NO3=1.8×101 and Kie-SO4=1.5×10−2, respectively. The results reported in this study suggest that although PIMs are capable of losing some membrane liquid phase when exposed to aqueous solutions, this loss can be minimized or even eliminated by increasing the solution concentration of the common anion.