The process of chloralkali (also chlor-alkali and chlor alkali ) is an industrial process for electrolysis of sodium chloride. It is a technology used to produce chlorine and sodium hydroxide (alkaline sodas), which are commodity chemicals needed by the industry. 35 million tons of chlorine was prepared by this process in 1987. Industrial scale production began in 1892.
Usually this process is done on saltwater (aqueous NaCl solution), in this case the yield of NaOH, hydrogen, and chlorine. When using calcium chloride or potassium chloride, the product contains calcium or non-sodium potassium. The associated process is known that using liquid NaCl to provide chlorine and sodium metal or viscous hydrogen chloride to produce hydrogen and chlorine.
This process has high energy consumption, for example over 4 billion kWh per year in West Germany in 1985. Since the process provides equal amounts of chlorine and sodium hydroxide (two moles of sodium hydroxide per mole of chlorine), it is necessary to find use for the product these products are in the same proportion. For every mole of chlorine produced, one mole of hydrogen is produced. Most of these hydrogens are used to produce hydrochloric acid or ammonia, or are used in the hydrogenation of organic compounds.
Video Chloralkali process
Sistem proses
Three production methods are in use. While mercury cell methods produce chlorine-free sodium hydroxide, the use of several tons of mercury causes serious environmental problems. In the normal production cycle, several hundred pounds of mercury per year is emitted, which accumulates in the environment. In addition, chlorine and sodium hydroxide produced by the mercury cell chloralkali process themselves are contaminated with small amounts of mercury. Membrane and diaphragm methods do not use mercury, but sodium hydroxide contains chlorine, which must be removed.
The performance of this device is governed by considerations of electrochemical engineering.
Membrane cell
The most common chloralkali process involves aqueous electrolysis of sodium chloride (salt water) in a membrane cell.
The saturated brine is passed to the first chamber of the cell where the chloride ion is oxidized on the anode, losing electrons to chlorine gas ( A in the figure):
- 2Cl - -> Cl
2 2e -
At the cathode, the positive hydrogen ions drawn from the water molecule are reduced by the electrons provided by the electrolytic current, to the hydrogen gas, releasing the hydroxide ions into the solution ( C in the figure):
- 2 H
2 O 2e - -> H 2 2OH -
The ion-permeable ion exchange membrane in the cell center allows the sodium (Na ) ions to pass into the second chamber where they react with the hydroxide ions to produce caustic soda (NaOH) ( B on picture). The overall reaction to saltwater electrolysis thus:
- 2NaCl 2 H
2 O -> Cl
2 H
2 2NaOH
Membrane cells are used to prevent reactions between chlorine and hydroxide ions. If this reaction occurs, chlorine will be disproportionate to form chloride and hypochlorite ions:
- Cl
2 2OH - -> Cl - ClO - H
2 O
Above about 60 ° C, chlorates can be formed:
- 3 Cl
2 6OH - -> 5Cl - ClO
3 - 3 H
2 O
Due to the corrosive nature of chlorine production, the anode (in which chlorine is formed) must be made of non-reactive metals such as titanium, whereas the cathode (in which the hydroxide form) can be made from more easily oxidized metals such as nickel.
Diaphragm cell
In the diaphragm cell process, there are two compartments separated by a permeable diaphragm, often made of asbestos fibers. Brine is inserted into the anode compartment and flows into the cathode compartment. Similar to Membrane Cells, chloride ions are oxidized on the anode to produce chlorine, and at the cathode, water is separated into caustic soda and hydrogen. Diaphragms prevent caustic soda reactions with chlorine. The dilute salt water dissolved leaving the cell. Caustic soda usually has to be concentrated to 50% and the salt is discarded. This is done using an evaporative process with about three tons of steam per ton of caustic soda. Salt separated from caustic salt water can be used to saturate dilute salt water. Chlorine contains oxygen and must be frequently purified by liquefaction and evaporation.
Mercury cells
In the process of mercury cells, also known as the Castner-Kellner process, a saturated salty water solution floats on a thin layer of mercury. Mercury is a cathode, in which sodium is produced and forms mercury-sodium-amalgam with mercury. The amalgam continues to be pulled out of the cell and reacts with water that decomposes amalgam into sodium hydroxide, hydrogen and mercury. Mercury is recycled into electrolytic cells. Chlorine is produced in the anode and evaporates out of the cell. Mercury cells are being removed due to concerns about mercury poisoning from mercury-cell contamination such as that occurring in Canada (see Ontario Minamata disease) and Japan (see Minamata disease).
Maps Chloralkali process
Manufacturers Association
The interests of chloralkali product producers are represented at the regional, national and international levels by associations such as Euro Chlor and The World Chlorine Council.
Laboratory procedures
Electrolysis can be carried out with a beaker, containing a brine solution (salt water) and containing pure water linked by a salt bridge. Anodes are made ideally from platinum metals, which are resistant to corrosion. Because corrosion is less severe on the cathode, it can be stainless or silver steel.
See also
- Gas diffusion electrode
- Electrochemical Engineering
- Solvay Process
References
Further reading
- Bommaraju, Tilak V.; Orosz, Paul J.; Sokol, Elizabeth A. (2007). "Brine Electrolysis." The Encyclopedia of Electrochemistry. Cleveland: Case Western Rsserve University.
Source of the article : Wikipedia
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