Bipolar Membrane Capacitive Deionization for pH-Assisted Ionic Separations

Abstract

Selective ionic separations represent an increasingly important technical area for the strategic interests of the U.S. economy�for example, securing critical minerals and materials and circular economy aspirations that include recovering organic acids from processed biomass. This work disseminates bipolar membrane (BPM) capacitive deionization for selective ionic separations from multicomponent, ionic species mixtures. The selective separations are guided by the Pourbaix diagram and acid−base equilibria principles. BPM capacitive deionization was demonstrated to generate alkaline or acidic process streams depending upon the location of the BPM in the electrochemical cell. The role of system operating parameters, such as the cell voltage, residence time, and feed concentration on effluent stream pH was studied. It was observed that the pH adjustment in BPM-CDI/ MCDI (MCDI, membrane capacitive deionization) was more sensitive to the cell voltage when compared to the process stream residence time and salt feed concentration. The BPM-MCDI gave over 6 times higher percentage of copper(II) removal when compared to sodium ion removal from brine mixtures. Finally, BPM-MCDI demonstrated over 40% greater removal for copper ions from brine mixtures and fivefold higher removal for itaconic acid from brine mixtures when benchmarked against a traditional flow-by-MCDI setup.

ACS Spotlight: Bipolar Membranes for Electrochemical Energy Conversion, Chemical Manufacturing, and Separations

“…(b) Bipolar membrane capacitive deionization (BPM-CDI) device for the selective removal of Cu from wastewater streams. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

“…BPMs can also be deployed in a capacitive deionization architecture (Figure b) to selectively recover metals, such as copper, from wastewater by carefully tuning the process stream pH and cell voltage . The separation scheme depicted in Figure b is informed by Pourbaix diagrams.…”

“…Our work in the field of BPMs can be broadly classified into two categories: Investigation of interfacial contact and area between the IEM layers and their effect on BPM polarization in a 4-point cell with supporting electrolyte, and computational studies for insights into the mechanism of water dissociation. ,,, Assessed BPMs in various electrochemical devices for separation (e.g., BPM-CDI) and energy conversion applications (fuel cells) and benchmarked their performance with their IEM equivalent configurations. , …”

E-Chem Education: A Crash Course in Electrochemical Engineering for Caustic Soda Plant Design

“…More recently, Arges et al demonstrated BPM membrane capacitive deionization (BPM MCDI) to make an alkaline process stream (i.e., aqueous sodium hydroxide) from an aqueous saline feed. 4 BPM MCDI does not generate hydrogen or oxygen gas and it uses low-cost carbon cloth electrodes.…”

Desalting Plasma Protein Solutions by Membrane Capacitive Deionization

“…Electrodialysis (ED), electrodeionization (EDI), and capacitive deionization (CDI)/membrane capacitive deionization (MCDI) are commercial electrochemical separation processes used for removing ions from solutions . In addition to being deployed for desalination, they have also been used for heavy metal ion removal, organic acid removal, nutrient recovery, and recovery of critical minerals. − Recent developments have seen these electrochemical platforms being adopted for deionization of small organic molecules such as lactic acid, p -coumaric acid, itaconic acid, and so forth as well as macromolecules (proteins, globulins, etc.) from biochemical feed streams. − In the context of deionizing plasma protein solutions, EDI is ill-suited because the unit features ion-exchange resins that are prone to fouling.…”