Electrochemical diaphragm flow cell

Reactor type Electrochemical micro flow cell Diaphragm material PTFE... 

Figure 4.30 Electrochemical micro reactor, a diaphragm micro flow cell, applied to perform the cation flow method. Assembled device (left). Disassembled device showing the two compartments of the cell within the housings and the diaphragm (right) [67. ...

Reactor 30 [R 30] Electrochemical Diaphragm Micro Flow Cell... 

Figure 5. Schematic of a diaphragm flow controlled trickle bed cell used by Dow Chemical Co. for the synthesis of hydrogen peroxide [24]. (By permission from The Electrochemical Society)...

Three main methods are used to keep these electrolytic products apart. One involves the separation of the electrochemical cell into two compartments by a porous vertical diaphragm, which permits the passage of brine and ions, but keeps the products separated. Another employs a flowing mercury cathode to continuously carry sodium, in the form of an amalgam, away from the brine and... 

Current density refers to the total current flow in kiloamperes divided by the anode electrode area in square meters, expressed as kA/m. High-current densities are desirable, particularly for electrochemical j rocesses, which yield unstable products. With current densities of 2-3 kA/m", electrolytic products of the diaphragm cell are rapidly moved from the sites of formation, which decreases side reactions and maximizes current efficiencies [14]. High-current densities, however, increase heat generation, anode wear, and the operating voltage so that lower current densities (and more cells) are better if the cells can be made cheaply. 

The sodium amalgam cathode product of the electrolyzer of the mercury cell is the chief difference between this and the diaphragm cell. The production of sodium hydroxide from this stream uses a separate set of electrochemical reactions conducted in a decomposer or denuder. This unit is usually located below the electrolyzer so as to allow gravity feed of the sodium amalgam from the electrolyzer to the top end of the decomposer (Fig. 8.4). Deionized water is fed into the bottom of the decomposer to provide countercurrent flows of sodium amalgam and water. Mercury, stripped (or denuded) of sodium, is continuously drawn off the bottom of the decomposer, and a hot solution of 50-70% sodium hydroxide in water, plus hydrogen gas, from the top. 

An interesting system is the methylene blue catalyzed oxidation of HS by O2 in a CSTR. Oscillation occurs over a narrow range of flow rates, and a mechanism has been proposed. Oscillations have also been found in the cobalt/bromide catalyzed oxidation of cyclohexanone by O2 in the electrochemical oxidation of HCHO and HCOOH/HCOO , and in the electrodissolution of copper in acidic chloride solution, and the anodic dissolution of nickel in aqueous sulfuric acid. °° Damped oscillations are predicted for reactions in stirred diaphragm cells. ... 

Because all electrochemical reactions involve anodic and cathodic reactions, polarization will have components for both reactions. As will be explained later, the electrode potentials have two terms for each electrode surface overpotential ija or ijc and concentration overpotential Apart from these overpotentials, electrical energy will also be expended due to the electrical resistance of the cell components such as electrolyte, diaphragm, busbar, etc. Thus the practical cell voltage (, when a net current is flowing through the cell, is the sum... 

The chlorine evolution reaction and the hydrogen evolution reaction at the anode and the cathode, respectively, in a chlor-alkali cell are controlled by the electrochemical and/or chemical steps rather than by mass transfer. However, the transport phenomena across the separator, either a porous diaphragm or an ion-exchange membrane, are governed by the solution flow near the surface. The disproportionation reaction of hypochlorites in a chlorate cell is diffusion-controlled process. Consequently, knowledge... 

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