The mercury cell

Used in the Chlor-Alkali industry to fabricate Cl, the quicksilver cell is an electrochemical cell? that is, a cell in which the decomposition of chemical compounds takes topographic point through electrolysis, with chemical alteration being produced in an electrolyte ( a solution that conducts electricity due to the presence of free ions ) by an electric current.

In the quicksilver cell ( or Castner-Kellner ) procedure, the electrolyte is present in the signifier of a concentrated seawater ( NaCl ) solution ( dwelling of Na+ and Cl- ions ) which floats on top of the quicksilver cathode. The current flows from the cell? s steel underside to the quicksilver. At the metal anodes ( hanging from the top of the cell ) , the seawater is electrolyzed and the undermentioned reaction takes topographic point to bring forth Cl: 2Cl- + Cl2 + 2 e- . Sodium is produced at the cathode ( Na+ + e- ? Na ) and so dissolves in quicksilver ( 2Na+ + 2Cl- ? 2Na ( in Hg ) + Cl ) to organize an amalgam ( a solid solution of metal in quicksilver ) . This amalgam is continuously removed from the cell and added to H2O, break uping it therefore into Na hydrated oxide, H gas and liquid quicksilver: 2Na ( in Hg ) + 2H2O? 2NaOH + H2 + Hg. The quicksilver is so recycled back into the cell to guarantee the continuance of the procedure.

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Efficiency

The most normally used procedure is non, if fact, the quicksilver cell ( which is on the contrary one of the least efficient methods of giving Cl ) , but the membrane cell, as it does non bring forth harmful waste merchandises. The quicksilver cell is non merely the least energy-efficient, but besides the most environmentally unfriendly, inasmuch as it produces much risky waste in the signifier of quicksilver. The same can be said of the stop cell, as it produces asbestos.

Hazards Associated With Operation

The most obvious hazard associated with the operation of the quicksilver cell and overall procedure of bring forthing Cl therewith is the fact that quicksilver is highly toxic, and, in countries where quicksilver waste from the quicksilver cell procedure is dumped, people tend to endure from related unwellnesss, such as serious methylmercury toxic condition ( finally ensuing in terrible neurological harm ) . In a broader sense, the fabrication of Cl airss hazards besides inasmuch as Cl is a extremely toxicant gas, and the procedure itself generates waste Waterss of hydrochloric acid and Na hydrated oxide. It is therefore important that those runing chlorine-producing workss look into invariably for escapes or inadvertent releases.

However, of late, the tendency has moved off from the quicksilver and stop cell processes towards more energy-efficient and safer membrane cell procedure. These yearss, merely 35 % of the Cl produced worldwide is made utilizing the quicksilver cell procedure. In add-on to this, quicksilver cell workss have stopped being built.

Merchandises Of The Chlor-Alkali Industry: Polymers

One of the most of import merchandises manufactured as a consequence of the Chlor-Alkali industry is polyvinyl chloride, a thermoplastic polymer more normally known as PVC. It is a strong, stiff, solid polymer with the monomer expression CH2=CHCl. The utilizations of PVC are apparently eternal? from window frames, pipe coating and shutters, to dally, food-packaging and waterproof-wear, PVC is apparently priceless in our daily lives.

PVC ( in fact polyvinyl chloride rosin ) is produced through the polymerisation of vinyl chloride monomer molecules, in bend made through the transition of ethylene bichloride at high temperatures. Ethylene bichloride is a combination of ethene and Cl ( the latter manufactured through membrane, quicksilver, and stop cell processes ) .

The polymerisation procedure followed is the same basic process as all other polymerisation: that is,

1. Initiation

2. Propagation

3. Termination

or

Another common polymer manufactured through the Chlor-Alkali procedure is polyvinylidene chloride ( PVDC ) or Saran A ( monomer expression: Ch2=CCl2 ) , a dense, high-melting solid with many utilizations, from cleaning-cloths, tape and unreal sod, to fishnetting and pyrotechnics.

However, despite the many benefits of polymers, there are a few cardinal disadvantages. With PVC, it is more a inquiry of environmental issues than anything else? polyvinyl chloride is non biodegradable, and generates dioxins when burnt for controlled waste recycling. In add-on to this, the hydrochloric acid which forms during the thermic decomposition of PVC has caused outcry amongst many conservationists, who are strongly promoting the usage of chlorine-free goods in the topographic point of PVC.

The same issues of non-biodegradability apply for polyvinylidene chloride, though in this instance the other disadvantage is much less terrible? at temperatures near to those of processing, Saran A undergoes dehydrochlorination. This consequences in the alteration of coloring material in the polymer from transparent or colorless to brown ; a most unwanted quality for the chief application of PVDC ; that is, nutrient packaging. As a consequence, of late, companies have been traveling off from the usage of PVDC.

On the whole, one can state that the advantages and disadvantages of the usage of Cl polymers by world largely equilibrate one another out, and the inquiry becomes one of happening a more environmentally friendly alternate for PVC ; presently a really of import and improbably utile polymer in our universe today.

REFERENCE LIST

Bommaraju, T. & A ; Orosz, P & A ; Sokol, E. 2007. Brine Electrolysis. Electrochemistry Encyclopedia ( online ) . Available:

hypertext transfer protocol: //electrochem.cwru.edu/encycl/art-b01-brine.htm 1 March 2010.

Hendricks, A. & A ; Sadeck, M. & A ; Spies, A. 2009. Concentrate On Physical Sciences. 11th erectile dysfunction. Cape Town: Maskew Miller Longman.

Mann, M. 2007. Physical Sciences 12: Textbook & A ; Workbook. Allcopy Publishers

Mercury Cell. 2010. Chloralkali Process ( online ) . Available:

hypertext transfer protocol: //en.wikipedia.org/wiki/Chloralkali_process # Mercury_cell 28 February 2010.

Polyvinyl Chloride ( PVC ) . 2009. Water Treatment Solutions ( online ) . Available: hypertext transfer protocol: //www.lenntech.com/polyvinyl-chloride-pvc.htm. 4 March 2010.

Polyvinylidene Chloride ( PVDC ) . 2010. Uses ( online ) . Available:

hypertext transfer protocol: //en.wikipedia.org/wiki/Polyvinylidene_chloride # Uses. 8 March 2010.

Procedure Details. 2009. Castner-Kellner Process ( online ) . Available: hypertext transfer protocol: //en.wikipedia.org/wiki/Castner-Kellner_process 28 February 2010.

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