11.3.Manufacturing Chlorine Using a Diaphragm and a Membrane

7/28/2019 11.3.Manufacturing Chlorine Using a Diaphragm and a Membrane

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6.1. describe the chemical processes involvedin the electrolysis of brine using a

diaphagm cell.6.2. discuss the economic advantages of

chlorine production by the diaphagm cellmethod.

6.3. discuss the industrial importance of thehalogens and their compounds.

6.4. assess the impact of the chlor-alkaliindustry on the environment.


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THE DIAPHRAGM CELL


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In the diaphragm cell chlorine is

manufactured by electrolysing concentratedsodium chloride solution; chlorine, sodiumhydroxide and hydrogen are producedsimultaneously.

At the anode: Chlorine gas is liberated

At the cathode: hydrogen gas is produced

Sodium hydroxide is leaving in the solution.


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At the anodeThe negative ions, chloride and hydroxide, get attracted towardsthe positively charged anode.More chloride ions arriving at the anode than hydroxide ions.

The major reaction at the anode is therefore:

At the cathodeSodium ions and hydrogen ions (from the water) are attracted to thenegative cathode. It is much easier for a hydrogen ion to pick up anelectron than for a sodium ion. So this reaction happens:


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The diaphragm is used to separate thechlorine liberated at the anode from thehydrogen and sodium hydroxide produce atthe cathode chamber.

Without the diaphragm to isolate them, thehydrogen and chlorine would ignitespontaneously and the sodium hydroxide andchlorine react forming sodium hypochlorite.

This mixture is commonly sold as bleach.

2NaOH(aq) + Cl2(g) NaOCl(aq) + NaCl(aq)


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The mercury cell


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The membrane cellThe membrane is

made from apolymer whichonly allowspositive ions topass through it.That means thatthe only thesodium ions fromthe sodium

chloride solutioncan pass throughthe membrane -and not the

chloride ions.


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DIAGRAMS CELLS

Advantage operating at a lower voltage then mercury cells and

with less pure brine than required by membrane andmercury cells.

produce chlorine gas with nearly no oxygen. the capital cost is relatively less expensive than the

mercury cell.

Disadvantages: The sodium hydroxide produce may need to be

evaporated to increase concentration and it givesrise to environmental releases of asbestos.


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USES OF CHLORINE Chlorine is used (generally a particular compound of

chlorine) to kill bacteria in drinking water and swimmingpools. It is also used in disinfectants and bleach for thesame reason. Chlorine is very effect against e coli bacteria.

Chlorine is used to make plastics. PVC (polyvinyl chloride) is made from chlorine. PVC is used

to make clothing, flooring, electrical cables, flexible hosesand tubing's, figurines (statues), waterbeds and inflatable

structures. Also, PVC is now being used to make ceilingtiles.

Chlorine is used in bromine extraction. Methyl chloride, another important compound of chlorine,

is used as an anaesthetic. It is also used to make certain

silicone polymers and is used to extract greases, oils andresins.

Chloroform, which contains chlorine, is used as a commonsolvent in science laboratories. It is also used to killmaggots in an animals wounds.

Trichloroethylene is used to degrease metal parts.


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INDUSTRIAL IMPORTANCE OF THE HALOGENS AND THEIR COMPOUNDS

FLUORINE has many uses such as making refrigerants,

detergents etc. Fluorine is used mainly for producing uraniumform hexafluoride and it is also used for making other fluorinecompounds.

Fluorine was used to produce CFC's and these CFC's were used

in aerosol sprays, cleaning agents and polymers. However itwas found that these compounds can cause ozone layerdepletion and so were banned. The most common of fluoride isin toothpaste.

The most important use of CHLORINE is as bleach for

manufacturing paper and cloth. The most common use ofchlorine is in drinking water and swimming pool as it can killharmful bacteria. Further uses of chlorine include production ofeveryday products such insecticides, solvents, food paints,plastic, dyes, textiles, petroleum products, paper products etc.


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BROMINE has an affinity to hydrogen, which makes it a gooddecomposer. Bromine is also used to disinfect water as it cankill the bacteria present in the water. The inorganic form ofbromine is used in photography film, bromine is also used infumigants, flame proofing agents, dyes and medicines.

IODINE is a very important element and has a lot of uses. Thecompounds are basically used in medicine, photography anddyes. Another very important use of iodine is as it is quite radioopaque, it can be used as X-ray radio contrast agent, forintravenous injection.

ASTATINE is not found in nature at all! It is produced bybombarding bismuth with alpha particles. The uses of astatineare not yet discovered but it is similar to iodine properties.

INDUSTRIAL IMPORTANCE OF THE HALOGENS AND THEIR COMPOUNDS


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IMPACT OF THE CHLOR-ALKALI INDUSTRY ON THE ENVIRONMENT.

Mercury emissionsBetween 1930 and 1960, several tons of mercurywaste was dumped in Japan. Thousands of peopleliving around the bay developed methylmercurypoisoning through the consumption of contaminatedfish. The victims suffered from severe neurological

damage. All told, thousands were afflicted and morethan 900 died. Since then, there was a significantmove away from mercury-cell technology todiaphragm and ion-exchange-membrane-cell

operations and currently only 35% of the worldcapacity (mostly in western and center Europe andabout 10% of U.S. production) of chlorine is producedusing the mercury-cell process. There will be no newconstruction of mercury-cell plants.


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CHEMISTRY FOR CAPE

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11.3.Manufacturing Chlorine Using a Diaphragm and a Membrane