A monovalent selective anion exchange membrane made by poly(2,6-dimethyl-1,4-phenyl oxide) for bromide recovery

Abstract

Bromide recovery from waste streams is crucial for both environmental and economic reasons. Membrane technology has shown great potential in achieving efficient ion separation, credited to the use of separation membranes with well-defined pore structure down to molecular level and surface charge properties. Herein, a class of novel anion exchange membranes (AEMs) was fabricated by brominated poly (2,6-dimethyl-1, 4-phenyl oxide) (BPPO) and different content of 4-hydroxy-1-methylpiperidine (HMP) via the chemical substitution reaction for Br- recovery. The resulting membrane (HMP@BPPO-0.1) had an ion exchange capacity of 1.69 mmol g−1, a water content of 14.4 %, a swelling rate of 4.7 %, a surface electrical resistance of 3.68 Ω cm2 and a limiting current density of 28.4 mA cm−2. In addition, under a constant voltage of 15.0 V for 180 min in electrodialysis, the removal ratio of NaBr solution was 98.15 %, which was higher than that of the commercial AEM (ASE) (97.1 %) under the same testing conditions. To evaluate the Br- selectivity, the membranes were tested for an initial concentration of 50 mM of NaCl, NaBr and Na2SO4 in a mixed solution with a constant current density of 2.5 mA cm−2, 5.0 mA cm−2 and 10.0 mA cm−2. The results showed that the permselectivity of the HMP@BPPO-0.1 for 100 min was as high as 12.6 (Br-/SO42-) and 1.20 (Br-/Cl-) under the 5.0 mA cm−2 electric field, and the ion permeation rate of Cl-, Br- and SO42- were 0.78, 1.20 and 0.20 mol−1 m-2 h−1, respectively. Compared to the ASE membrane and the resulting membrane with negatively charged modification layer, this work suggests novel ideas in fabricating a membrane with Br- selectivity in view of resource recovery.