Electrodialysis Essay

The electrodialysis setup consists of: an ED cell, a power DC, a brine tank, a feed tank, an electrode rinse tank, three centrifugal pumps (P = 84W, total head = 4.2 m) equipped each with a flowmeter and three valves to control feed flow rate. Fig. 2 shows a simplified diagram of the electrodialysis setup working in continuous mode.

Fig. 2 Schematic of the electrodialysis system used in this study.

The electrodialysis operation was carried out on a laboratory stack “PCCell ED 64 002” supplied by PCA-Polymerchemie Altmeier GmbH and PCCell GmbH, Heusweiler, Germany. As shown in Fig 3, ED cell is packed with ion exchange membranes (cation and anion), spacers and a pair of electrodes (anode and cathode). Both electrodes are made of Pt/Ir - coated Titanium. The membranes and spacers are stacked between the two electrode-end blocks. Plastic separators are placed between the membranes to form the flow paths of the dilute and concentrate streams. These spacers are designed to minimize boundary layer effects and are arranged in the stack so that all the dilute and concentrate streams are manifolded separately. In this way a repeating section called a cell pair is formed; it consists of a cation exchange membrane, a dilute flow spacer, an anion-exchange membrane, and a concentrate flow spacer. In this work, experiments were carried out by this stack equipped with three cation exchange membranes (CEM) and two anion exchange membranes (AEM).

For each membrane, the active surface area is 0.0064 m2 and the flow channel width between two membranes is 0.5 mm.

Fig. 3 Schematic of the ED cell used in this study.

PC-SK standard cation exchange membranes and PC-SA standard anion exchange membranes are used in the stack. Information given by the manu...

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... the applied potential, I the applied current, V the dilute stream volume and t is the time.

2.5.5. The current efficiency CE

The mole number of an ion crossing the membrane from the dilute to the concentrate solutions during the time t is compared to the number of faradays involved in the operation. The ratio of the two numbers is called current efficiency.

The current efficiency is an important parameter that determines the optimum range of applicability of electrodialysis. It is a measure of how effective ions are transported across the ion exchange membranes for a given applied current. It is calculated using the following equation [20, 21]:

CE=(∆N_A.F)/Q

Where NA is the equivalent number of A transferred per cell during the interval of time t, Q the current quantity supplied to the system during the same time and F is the Faraday constant (96 485 A s mol−1).