How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

Natalia Pismenskaya; Olesya Rybalkina; Ksenia Solonchenko; Evgeniia Pasechnaya; Veronika Sarapulova; Yaoming Wang; Chenxiao Jiang; Tongwen Xu; Victor Nikonenko

doi:10.3390/polym15102288

How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

Polymers (Basel). 2023 May 12;15(10):2288. doi: 10.3390/polym15102288.

Authors

Natalia Pismenskaya¹, Olesya Rybalkina¹, Ksenia Solonchenko¹, Evgeniia Pasechnaya¹, Veronika Sarapulova¹, Yaoming Wang², Chenxiao Jiang², Tongwen Xu², Victor Nikonenko¹

Affiliations

¹ Russian Federation, Kuban State University, 149, Stavropolskaya Str., 350040 Krasnodar, Russia.
² Anhui Provincial Engineering Laboratory of Functional Membrane Science and Technology, Department of Applied Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China.

Abstract

Innovative ion exchange membranes have become commercially available in recent years. However, information about their structural and transport characteristics is often extremely insufficient. To address this issue, homogeneous anion exchange membranes with the trade names ASE, CJMA-3 and CJMA-6 have been investigated in Na_xH_(3-x)PO₄ solutions with pH 4.4 ± 0.1, 6.6 and 10.0 ± 0.2, as well as NaCl solutions with pH 5.5 ± 0.1. Using IR spectroscopy and processing the concentration dependences of the electrical conductivity of these membranes in NaCl solutions, it was shown that ASE has a highly cross-linked aromatic matrix and mainly contains quaternary ammonium groups. Other membranes have a less cross-linked aliphatic matrix based on polyvinylidene fluoride (CJMA-3) or polyolefin (CJMA-6) and contain quaternary amines (CJMA-3) or a mixture of strongly basic (quaternary) and weakly basic (secondary) amines (CJMA-6). As expected, in dilute solutions of NaCl, the conductivity of membranes increases with an increase in their ion-exchange capacity: CJMA-6 < CJMA-3 << ASE. Weakly basic amines appear to form bound species with proton-containing phosphoric acid anions. This phenomenon causes a decrease in the electrical conductivity of CJMA-6 membranes compared to other studied membranes in phosphate-containing solutions. In addition, the formation of the neutral and negatively charged bound species suppresses the generation of protons by the "acid dissociation" mechanism. Moreover, when the membrane is operated in overlimiting current modes and/or in alkaline solutions, a bipolar junction is formed at the CJMA- 6/depleted solution interface. The CJMA-6 current-voltage curve becomes similar to the well-known curves for bipolar membranes, and water splitting intensifies in underlimiting and overlimiting modes. As a result, energy consumption for electrodialysis recovery of phosphates from aqueous solutions almost doubles when using the CJMA-6 membrane compared to the CJMA-3 membrane.

Keywords: anion exchange membrane; bound species; conductivity; current–voltage curve; electrodialysis; energy consumption; phosphates; proton generation; structure; weakly basic fixed groups.

Grants and funding

21-19-00087/Russian Science Foundation