Bipolar Electrodialyzer (EDBM)

Three chambers(triplet) Electrodialyzer BPED

In a Bipolar Electrodialyzer (EDBM), a triplet (also called a "cell" or "repetitive unit") is the fundamental repeating unit of a 3-compartment (chambers) membrane stack. It is specifically designed to convert salts into their corresponding acids and bases through water dissociation. It consists of three specific membranes and three corresponding liquid channels that work together to convert a salt into its constituent acid and base.

Components of a Triplet

A standard three-compartment triplet consists of three different ion-exchange membranes and three flow channels:
Membranes:
Bipolar Membrane (BPM): The "engine" of the system. It consists of an anion-selective layer and a cation-selective layer together. Under an electric field, it forces water molecules to split into H+and OH- ions at its internal interface and its junction.
Anion-Exchange Membrane (AEM): Allows negatively charged ions (anions) to pass through.
Cation-Exchange Membrane (CEM): Allows positively charged ions (cations) to pass through.
Channels (Solution Compartments):
Acid Channel: Where H+ from the BPM combines with anions from the salt channel to form acid.
Alkaline/Base Channel: Where OH- from the BPM combines with cations from the salt channel to form base.
Salt/Saline Channel: Where the feed salt solution is depleted of its ions.

Working Principle

Water Dissociation: When a direct current is applied, water molecules at the interface of the BPM layers split into protons H+and hydroxide ions OH-.
Ion Migration: The applied electric field forces cations from the salt channel through the CEM into the base channel, and anions through the AEM into the acid channel.
Chemical Production: The migrated salt ions combine with the generated H+ andOH- to produce concentrated acid and base solutions.

How the Three Compartments Work

The membranes create three distinct flow channels within the triplet(3 chambers):
Salt Channel (Feed): Located between the AEM and CEM. As current flows, salt cations M+ move through the CEM toward the cathode, and salt anions X- move through the AEM toward the anode. This "desalinates" the feed stream.
Acid Channel: Located between the AEM and the cation side of the BPM. The BPM injects H+ ions into this channel, while the salt anions X- enter from the salt channel. Together, they form the acid HX.
Base Channel: Located between the CEM and the anion side of the BPM. The BPM injects OH- ions here, while salt cations M+ enter from the salt channel, forming the base MOH

Why Use a Triplet?

The triplet configuration is the "gold standard" for salt splitting for several reasons:
High Purity: Because the acid and base are formed in separate dedicated compartments, there is minimal contamination between the two.
Simultaneous Action: It performs three tasks at once: it produces acid, produces base, and dilutes the original salt stream.
Versatility: It can process inorganic salts (like Na2SO4 into h2SO4 and NaOH or organic salts (like sodium lactate into lactic acid).