Current efficiency diaphragm cell

Current Efficiency. Current efficiency for caustic production in diaphragm and membrane cells can be estimated from collection of a known amount of caustic over a period of time and from a knowledge of the number of coulombs of electricity passed during that time period. An alternative method involves analysis of the gases evolved during electrolysis and determining the anolyte composition. Material balance considerations (7) show the expression for the caustic efficiency for membrane cells to be... 

Metal Anode Diaphragm Cathode Cell feed g/L Electrolyte, g/L Temperat ure, °C CeU voltage, V Cathode current density, A/m Energy requirement, kWh/kg Current efficiency, %... 

An account of cell features should make a reference to the diaphragm. The diaphragm used in some electrolytic processes is essentially constituted of a separator wall, though this allows the free passage of the electric current. It performs the important function of preventing the products of electrolysis formed at the anode from coming into contact with those formed at the cathode so as to avoid, as far as feasible, either secondary reactions which would lower the current efficiency, or contamination of the products which would diminish their value. 

The first electrochemical application of the D -statistic deals with the lack- of-association (i.e. independence) hypothesis concerning current efficiency and current load in diaphragm-type industrial scale chlor-alkali cells [18], Table 5 demonstrates that the two factors are independent with the understanding that the current efficiency/current load relationship may indirectly be influenced by other technical variables, e g. cell potential, and impurities. 

Table 5. Testing the independence of current efficiency and current load via eight different diaphragm-type chlor-alkali cells [18]...

Sodium orthoarsenate is also obtained electrolytically by the method described under calcium arsenate (p. 198). Yields up to 100 per cent, may be obtained 9 by employing a cell with a diaphragm between iron electrodes. The anolyte should contain sodium arsenite, or sodium hydroxide and arsenious oxide (equivalent to 150 g. As2Os per litre), and the catholyte sodium hydroxide (150 g. per litre). With a current density of 3 amps, per sq. dm. the current efficiency is 100 per cent. A solid crust of sodium arsenate forms around the anode. The process may be rendered continuous by circulating the anolyte and removing the precipitated arsenate. Iron or nickel electrodes are... 

Figure 064. Apparatus for running more then 1 cell on the same power supply to maximum current efficiency. This in series type operation can be used for any electrolysis procedure, even if using a diaphragm cell, and is not restricted sole to copper-I-...

Overall Energy Consumption. The voltage efficiency is the ratio of the thermodynamic decomposition voltage to the actual cell voltage ( cell) eiieigV efficiency (nener )> which is a product of the current and voltage efficiencies, can be expressed for a diaphragm cell as... 

The saturated (about 300 g/L NaCl) pretreated brine is preheated to about 90°C and fed to the anode compartment as a broken stream, broken in order to avoid electrical losses. Preheating the brine both increases cell conductivity by increasing ion mobility with the lower solution viscosity, and decreases chlorine solubility in the brine. In this way less dissolved chlorine is carried through the diaphragm in the percolating brine, which contributes to higher cell current efficiencies and lower concentrations of impurities in the... 

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. 

Other remaining technical concerns with membrane cells relate to somewhat lower current efficiencies and to relatively short membrane lifetimes. At present, this is limited to 2-3 year of operation when coupled to much more careful brine pretreatment than is required for conventional asbestos diaphragm cells. A combination of mercury cell and membrane cell technologies has been recently tested for commercial feasibility [19]. The economics of the three primary chloralkali technologies have also been reviewed [20]. 

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