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Castner-Kellner process
 
 
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The Castner-Kellner process is a method of electrolysis
Electrolysis

In chemistry and manufacturing, electrolysis is a method of separating Chemical bond chemical compound by passing an electric current through them....
 on an aqueous alkali
Alkali

In chemistry, an alkali is a Base , Ionic compound salt of an alkali metal or alkaline earth metal Chemical element. Alkalis are best known for being Base s that dissolve in water....
 chloride
Chloride

The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....
 solution (usually sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
 solution) to produce the corresponding alkali hydroxide
Hydroxide

In chemistry, hydroxide is the name for the Diatomic molecule anion OH-, consisting of oxygen and hydrogen atoms, usually derived from the Dissociation of a base ....
, invented by Hamilton Castner
Hamilton Castner

Hamilton Young Castner was an American industrial chemist.He was born in Brooklyn, New York and educated at the Polytechnic University of New York, then at the Fu Foundation School of Engineering and Applied Science....
 and Karl Kellner in the 1890s.

apparatus shown is divided into two types of cells separated by slate
Slate

Slate is a fine-grained, foliation , homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcano ash through low grade regional metamorphism....
 walls. The first type, shown on the right and left of the diagram, uses an electrolyte of sodium chloride solution, a graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
 anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 (A), and a mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
 cathode
Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
 (M).






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Encyclopedia


The Castner-Kellner process is a method of electrolysis
Electrolysis

In chemistry and manufacturing, electrolysis is a method of separating Chemical bond chemical compound by passing an electric current through them....
 on an aqueous alkali
Alkali

In chemistry, an alkali is a Base , Ionic compound salt of an alkali metal or alkaline earth metal Chemical element. Alkalis are best known for being Base s that dissolve in water....
 chloride
Chloride

The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....
 solution (usually sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
 solution) to produce the corresponding alkali hydroxide
Hydroxide

In chemistry, hydroxide is the name for the Diatomic molecule anion OH-, consisting of oxygen and hydrogen atoms, usually derived from the Dissociation of a base ....
, invented by Hamilton Castner
Hamilton Castner

Hamilton Young Castner was an American industrial chemist.He was born in Brooklyn, New York and educated at the Polytechnic University of New York, then at the Fu Foundation School of Engineering and Applied Science....
 and Karl Kellner in the 1890s.

Process details

The apparatus shown is divided into two types of cells separated by slate
Slate

Slate is a fine-grained, foliation , homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcano ash through low grade regional metamorphism....
 walls. The first type, shown on the right and left of the diagram, uses an electrolyte of sodium chloride solution, a graphite
Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek language ??afe?? : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead....
 anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 (A), and a mercury
Mercury (element)

Mercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure....
 cathode
Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
 (M). The other type of cell, shown in the center of the diagram, uses an electrolyte of sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
 solution, a mercury anode (M), and an iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 cathode (D). Note that the mercury electrode is shared between the two cells. This is achieved by having the walls separating the cells dip below the level of the electrolytes but still allow the mercury to flow beneath them.

The reaction at anode (A) is:

2Cl– ? Cl2 + 2e–


The chlorine
Chlorine

Chlorine...
 gas that results vents at the top of the outside cells where it is collected as a byproduct of the process. The reaction at the mercury cathode in the outer cells is

2Na+ + 2e– ? 2Na (amalgam)


The sodium
Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
 metal formed by this reaction dissolves in the mercury to form an amalgam
Amalgam

Amalgam may refer to:* Amalgam , mercury alloy* Amalgam , material of "silver" tooth fillings* Amalgam Comics, publisher* Amalgam, Gauteng, South Africa...
. The mercury conducts the current from the outside cells to the center cell. In addition, a rocking mechanism (B shown by fulcrum on the left and rotating eccentric on the right) agitates the mercury to transport the dissolved sodium metal from the outside cells to the center cell.

The anode reaction in the center cell takes place at the interface between the mercury and the sodium hydroxide solution.

2Na (amalgam) ? 2Na+ + 2e–


Finally at the iron cathode (D) of the center cell the reaction is

2H2O + 2e– ? 2OH– + H2


The net effect is that the concentration of sodium chloride in the outside cells decreases and the concentration of sodium hydroxide in the center cell increases. As the process commences some sodium hydroxide solution is withdrawn from center cell as output product and is replaced with water. Sodium chloride is added to the outside cells to replace what has been electrolized.

History

The first patent for electrolyzing brine
Brine

File:Kissingen-Solepumpe-1848.JPGFile:Kissingen-Solepumpe-1848-2.JPGBrine is water Saturation or nearly saturated with a Salt .It is used to preserve vegetables, fish, and meat, in a process known as brining ....
 was granted in England
England

native_name =|conventional_long_name = England|common_name = England|image_flag = Flag of England.svg|image_coat = England COA.svg|symbol_type = Royal Coat of Arms...
 in 1851 to Charles Watt. His process was not an economically feasible method for producing sodium hydroxide though because it could not prevent the chlorine that formed in the brine solution from reacting with its other constituents. Hamilton Castner
Hamilton Castner

Hamilton Young Castner was an American industrial chemist.He was born in Brooklyn, New York and educated at the Polytechnic University of New York, then at the Fu Foundation School of Engineering and Applied Science....
 solved the mixing problem with the invention of the mercury cell and was granted a U.S. patent in 1892. Austrian chemist, Karl Kellner arrived at a similar solution at about the same time. In order to avoid a legal battle they became partners in 1895, founding the Castner-Kellner Alkali Company, which built plants employing the process throughout Europe. The mercury cell process continues in use to this day. Current-day mercury cell plant operations are criticized for environmental release of mercury leading in some cases to severe mercury poisoning
Mercury poisoning

Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a Heavy metal which occurs in several forms, all of which can produce toxic effects in high enough doses....
 as occurred in Ontario Minamata disease
Ontario Minamata disease

Ontario Minamata disease is a neurology syndrome caused by severe mercury poisoning. It occurred in Ontario, Canada in 1970 and severely affected two First Nation communities located in Northwestern Ontario following consumption of local fish that were contaminated with mercury and one First Nation in Southern Ontario due to illegal disposal...
. Due to these concerns, mercury cell plants are being phased out, and a sustained effort is being made to reduce mercury emissions from existing plants.

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