Diaphragm cells cathode efficiency

Increases operating voltage reduces diaphragm-cell current efficiency promotes hydrogen formation on mercury cathode Reduces current efficiency and increases operating voltage disrupts membrane Same as calcium (see above)... 

Diaphragm or membrane cells are used in special cases where impurities are easily codeposited on the cathode, anode slimes are a problem, or the anolyte and catholyte have a different composition. A diaphragm cell can be made by enclosing either the anodes or the cathodes in a rigid bag. Enclosing anodes in a bag is an efficient method to collect anode slimes, but the anode compartments must be cleaned quite often. Enclosing cathodes in a bag requires purification of the anolyte in a... 

Ch/ NaOH Appendix 4.4.1). Note that the hydrogen inefficiency arises from the BCLs due to the discharge of the available chlorine at the cathode. However, the chlor-alkali industry routinely measures only the chlorine current efficiency of diaphragm cells using the relationship in Eq. (92) detailed in [1,7,13]. 

While cathode reactions tend to be quite efficient, low concentrations of mercury and oxygen may be objectionable. Sections 9.2.5.1 and 9.2.5.2 deal with their removal. Volatile impurities in the catholyte may also contaminate the hydrogen. This is most likely in diaphragm cells, and Section 7.5.8.5 gave an example in which the removal of ammonia from brine reduced the concentrations of chloramines and other nitrogen compounds in the hydrogen. 

It is also possible to electrolyse a solution containing iron in the ferrous state in a compartmented-diaphragm cell. Ferrous iron will not interfere with the cathode reactions but will be oxidised to ferric iron in the anode compartment. To achieve this, feed solution enters the cathode compartment and electrolyte passes through the diaphragm, constructed of an inert fabric, to the anode compartment and exits the cell. The anolyte can then be reused for leaching. Any escape or return of ferric iron to the cathode compartment will result in its reduction to ferrous iron in preference to lead deposition, thus reducing process current efficiency for lead recovery. 

The diaphragm cell (Figure 3.2) is so called because the anode and cathode compartments are separated by an asbestos diaphragm. This is designed to prevent contamination of the anode compartment by the products formed at the cathode. In addition to the fundamental reactions occurring at the anode and cathode the following may take place, reducing the current efficiency of the process. 

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. 

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