How is sodium hypochlorite generation done?

Anion

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For the neutral chemical compound, see chlorine monoxide

Chemical compound

In chemistry, hypochlorite, or chloroxide is an anion with the chemical formula ClO&#;. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of bleaching powder, swimming pool "chlorine").[1] The Cl-O distance in ClO&#; is 1.69 Å.[2]

The name can also refer to esters of hypochlorous acid, namely organic compounds with a ClO&#; group covalently bound to the rest of the molecule. The principal example is tert-butyl hypochlorite, which is a useful chlorinating agent.[3]

Most hypochlorite salts are handled as aqueous solutions. Their primary applications are as bleaching, disinfection, and water treatment agents. They are also used in chemistry for chlorination and oxidation reactions.

Reactions

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Acid reaction

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Acidification of hypochlorites generates hypochlorous acid, which exists in an equilibrium with chlorine. A lowered pH (ie. towards acid) drives the following reaction to the right, liberating chlorine gas, which can be dangerous:

2 

H

+

+

ClO

&#;

+

Cl

&#;

&#;

Cl

2

+

H

2

O

Stability

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Hypochlorites are generally unstable and many compounds exist only in solution. Lithium hypochlorite LiOCl, calcium hypochlorite Ca(OCl)2 and barium hypochlorite Ba(ClO)2 have been isolated as pure anhydrous compounds. All are solids. A few more can be produced as aqueous solutions. In general the greater the dilution the greater their stability. It is not possible to determine trends for the alkaline earth metal salts, as many of them cannot be formed. Beryllium hypochlorite is unheard of. Pure magnesium hypochlorite cannot be prepared; however, solid Mg(OH)OCl is known.[4] Calcium hypochlorite is produced on an industrial scale and has good stability. Strontium hypochlorite, Sr(OCl)2, is not well characterised and its stability has not yet been determined.[citation needed]

Upon heating, hypochlorite degrades to a mixture of chloride, oxygen, and chlorates:

2 

ClO

&#;

&#; 2 

Cl

&#;

+

O

2

3 

ClO

&#;

&#; 2 

Cl

&#;

+

ClO

&#;
3

This reaction is exothermic and in the case of concentrated hypochlorites, such as LiOCl and Ca(OCl)2, can lead to dangerous thermal runaway and is potentially explosive.[5]

The alkali metal hypochlorites decrease in stability down the group. Anhydrous lithium hypochlorite is stable at room temperature; however, sodium hypochlorite is explosive as an anhydrous solid.[6] The pentahydrate (NaOCl·(H2O)5) is unstable above 0 °C;[7] although the more dilute solutions encountered as household bleach are more stable. Potassium hypochlorite (KOCl) is known only in solution.[4]

Lanthanide hypochlorites are also unstable; however, they have been reported as being more stable in their anhydrous forms than in the presence of water.[8] Hypochlorite has been used to oxidise cerium from its +3 to +4 oxidation state.[9]

Hypochlorous acid itself is not stable in isolation as it decomposes to form chlorine. Its decomposition also results in some form of oxygen.

Reactions with ammonia

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Hypochlorites react with ammonia first giving monochloramine (NH
2Cl), then dichloramine (NHCl
2), and finally nitrogen trichloride (NCl
3).[1]

NH

3

+

ClO

&#;

&#;

HO

&#;

+

NH

2

Cl

NH

2

Cl +

ClO

&#;

&#;

HO

&#;

+

NHCl

2

NHCl

2

+

ClO

&#;

&#;

HO

&#;

+

NCl

3

Preparation

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Hypochlorite salts

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Hypochlorite salts formed by the reaction between chlorine and alkali and alkaline earth metal hydroxides. The reaction is performed at close to room temperature to suppress the formation of chlorates. This process is widely used for the industrial production of sodium hypochlorite (NaClO) and calcium hypochlorite (Ca(ClO)2).

Cl2 + 2 NaOH &#; NaCl + NaClO + H2O

2 Cl2 + 2 Ca(OH)2 &#; CaCl2 + Ca(ClO)2 + 2 H2O

Large amounts of sodium hypochlorite are also produced electrochemically via an un-separated chloralkali process. In this process brine is electrolyzed to form Cl
2 which dissociates in water to form hypochlorite. This reaction must be conducted in non-acidic conditions to prevent release of chlorine:

2 

Cl

&#;

&#;

Cl

2

+ 2 e&#;

Cl

2

+

H

2

O

The company is the world’s best electrolytic sodium hypochlorite generator supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

&#;

HClO

+

Cl

&#;

+

H

+

Some hypochlorites may also be obtained by a salt metathesis reaction between calcium hypochlorite and various metal sulfates. This reaction is performed in water and relies on the formation of insoluble calcium sulfate, which will precipitate out of solution, driving the reaction to completion.

Ca(ClO)2 + MSO4 &#; M(ClO)2 + CaSO4

Organic hypochlorites

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Hypochlorite esters are in general formed from the corresponding alcohols, by treatment with any of a number of reagents (e.g. chlorine, hypochlorous acid, dichlorine monoxide and various acidified hypochlorite salts).[3]

Biochemistry

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Biosynthesis of organochlorine compounds

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Chloroperoxidases are enzymes that catalyzes the chlorination of organic compounds. This enzyme combines the inorganic substrates chloride and hydrogen peroxide to produce the equivalent of Cl+, which replaces a proton in hydrocarbon substrate:

R-H + Cl&#; + H2O2 + H+ &#; R-Cl + 2 H2O

The source of "Cl+" is hypochlorous acid (HOCl).[11] Many organochlorine compounds are biosynthesized in this way.

Immune response

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In response to infection, the human immune system generates minute quantities of hypochlorite within special white blood cells, called neutrophil granulocytes.[12] These granulocytes engulf viruses and bacteria in an intracellular vacuole called the phagosome, where they are digested.

Part of the digestion mechanism involves an enzyme-mediated respiratory burst, which produces reactive oxygen-derived compounds, including superoxide (which is produced by NADPH oxidase). Superoxide decays to oxygen and hydrogen peroxide, which is used in a myeloperoxidase-catalysed reaction to convert chloride to hypochlorite.[13][14][15]

Low concentrations of hypochlorite were also found to interact with a microbe's heat shock proteins, stimulating their role as intra-cellular chaperone and causing the bacteria to form into clumps (much like an egg that has been boiled) that will eventually die off.[16] The same study found that low (micromolar) hypochlorite levels induce E. coli and Vibrio cholerae to activate a protective mechanism, although its implications were not clear.[16]

In some cases, the base acidity of hypochlorite compromises a bacterium's lipid membrane, a reaction similar to popping a balloon.[citation needed]

Industrial and domestic uses

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Hypochlorites, especially of sodium ("liquid bleach", "Javel water") and calcium ("bleaching powder") are widely used, industrially and domestically, to whiten clothes, lighten hair color and remove stains. They were the first commercial bleaching products, developed soon after that property was discovered in by French chemist Claude Berthollet.

Hypochlorites are also widely used as broad spectrum disinfectants and deodorizers. That application started soon after French chemist Labarraque discovered those properties, around (still before Pasteur formulated his germ theory of disease).

Laboratory uses

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As oxidizing agents

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Hypochlorite is the strongest oxidizing agent of the chlorine oxyanions. This can be seen by comparing the standard half cell potentials across the series; the data also shows that the chlorine oxyanions are stronger oxidizers in acidic conditions.[17]

Ion Acidic reaction E° (V) Neutral/basic reaction E° (V) Hypochlorite H+ + HOCl + e&#; &#;

1

&#;

2

 Cl2(g) + H2O 1.63 ClO&#; + H2O + 2 e&#; &#; Cl&#; + 2OH&#; 0.89 Chlorite 3 H+ + HOClO + 3 e&#; &#;

1

&#;

2

 Cl2(g) + 2 H2O 1.64

ClO

&#;
2

+ 2 H2O + 4 e&#; &#; Cl&#; + 4 OH&#; 0.78 Chlorate 6 H+ +

ClO

&#;
3

+ 5 e&#; &#;

1

&#;

2

 Cl2(g) + 3 H2O 1.47

ClO

&#;
3

+ 3 H2O + 6 e&#; &#; Cl&#; + 6 OH&#; 0.63 Perchlorate 8 H+ +

ClO

&#;
4

+ 7 e&#; &#;

1

&#;

2

 Cl2(g) + 4 H2O 1.42

ClO

&#;
4

+ 4 H2O + 8 e&#; &#; Cl&#; + 8 OH&#; 0.56

Hypochlorite is a sufficiently strong oxidiser to convert Mn(III) to Mn(V) during the Jacobsen epoxidation reaction and to convert Ce3+
to Ce4+
.[9] This oxidising power is what makes them effective bleaching agents and disinfectants.

In organic chemistry, hypochlorites can be used to oxidise primary alcohols to carboxylic acids.[18]

As chlorinating agents

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Hypochlorite salts can also serve as chlorinating agents. For example, they convert phenols to chlorophenols. Calcium hypochlorite converts piperidine to N-chloropiperidine.

Related oxyanions

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Chlorine can be the nucleus of oxyanions with oxidation states of &#;1, +1, +3, +5, or +7. (The element can also assume oxidation state of +4 is seen in the neutral compound chlorine dioxide ClO2).

Chlorine oxidation state &#;1 +1 +3 +5 +7 Name chloride hypochlorite chlorite chlorate perchlorate Formula Cl&#; ClO&#;

ClO

&#;
2

ClO

&#;
3

ClO

&#;
4

Structure

See also

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References

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Sodium Hypochlorite Generator works on electrochlorination chemical process which uses water, common salt and electricity to produce Sodium Hypochlorite(NaOCl). The brine solution (or sea water) is made to flow through an electrolyzer cell, where direct current is passed which leads to Electrolysis. This produces Sodium Hypochlorite instantaneously which is a strong disinfectant. This is then dosed in water in the required concentration to disinfect water, or to prevent Algae Formation and Bio Fouling. Pristine Water is the leading manufacturer of On-site Sodium Hypochlorite Generator.

Operating Principle:

In the Electrolyser, the current is passed through the anode and cathode in the salt solution. which is a good conductor of electricity, thus electrolyzing the sodium chloride solution.

This results in chlorine (Cl2) gas being produced at the anode, while sodium hydroxide (NaOH) and hydrogen (H2) gas is produced at the cathode.

The reactions that take place in the electrolytic cell is:

2 NaCl + 2 H2O = 2 NaOH + Cl2 + H2

The chlorine further reacts with the hydroxide to form sodium hypochlorite (NaOCl). This reaction can be simplified in the following manner:

Cl2 + 2 NaOH = NaCl + NaClO + H2O

The solution generated has a pH value between 8 and 8.5, and a maximum equivalent chlorine concentration of less than 8 g/l. It has a very long shelf life which makes it suitable for storage.

After dosing the solution into the water flow, no pH value correction is necessary, as is often required in sodium hypochlorite produced by the membrane method. The sodium hypochlorite solution reacts in a balance reaction, resulting in hypochlorous acid:

NaClO + H2O = NaOH + HClO

To produce 1kg equivalent of chlorine using an on-site Sodium Hypochlorite generator, 4.5 kg of salt and 4-kilowatt hours of electricity is required. The final solution consists of approximately 0.8% (8 grams/liter) sodium hypochlorite.

Specification:

• Simple: Only water, salt, and electricity is required
• Non-Toxic: Common salt which is the main substance is non-toxic and easy to store. Electro chlorinator provides the power of Chlorine without the danger of storing or handling hazardous materials.
• Low Cost: only water, common salt, and electricity is needed for electrolysis. The total operating cost of an Electrochlorinator is less than the conventional Chlorination methods.
• Easy to dose to get a standard concentration: Sodium hypochlorite generated on-site does not degrade like commercial sodium hypochlorite. Therefore, the dosage need not be modified on a daily basis based on the strength of the hypo solution.
• Approved disinfection method complying with the drinking water regulations &#; an alternative with fewer safety requirements to chlorine-gas-based systems.
• Long service life, as compared with the membrane cell electrolysis
• On-site generation of sodium hypochlorite allows the operator to produce the only which is needed and when it is needed.
• Safe for the Environment: As compared to 12.5% sodium hypochlorite, the use of salt and water reduces carbon emission to 1/3rd. The hypo solution of less than 1% concentration produced by our system is benign and considered non-hazardous. This translates to reduced safety training and improved worker safety.

Sodium Hypochlorite generated on-site with the help of synthetic brine or seawater is very efficient in protecting the equipment from the growth of micro-organic fouling and control of algae and crustaceans. Compact Electrochlorinators manufactured by Pristine Water are ideal for the disinfection of water during disasters like earthquakes, Floods, or Epidemics. Electrochlorinators are designed for rural and village &#;point-of-use&#; disinfection of drinking water.

Advantages of On-Site Sodium Hypochlorite Generator:

Although the economic consideration is the major advantage in using On-site generated Sodium Hypochlorite over the use of other forms of Chlorination, the technical advantages are even greater.

The following are some of the problems associated with using commercial-grade liquid sodium hypochlorite. These have a high concentration (10-12%) of active chlorine. These are produced by bubbling gas chlorine in Caustic soda (Sodium Hydroxide). They are also commonly called Liquid Chlorine.

Corrosion

The corrosion due to Commercially produced hypochlorite is a concern because of its effect on the equipment. A 10 to 15% hypochlorite solution is very aggressive due to its high pH and chlorine concentration. Because of its aggressive nature, the hypochlorite solution will exploit any weakened areas in the hypochlorite piping system and may cause leaks. So using an On-site sodium Hypochlorite generator is a wise option.

Scaling

The formation of calcium carbonate scale is another concern when using commercial grade liquid hypochlorite for chlorination. Commercial grade liquid hypochlorite has a high pH. When the high pH hypochlorite solution is mixed with the dilution water, it raises the pH of the mixed water to above 9. The calcium in the water will react and precipitate out as calcium carbonate scale. Items such as pipes, valves, and rotameters may scale up and no longer function properly. It is recommended that the commercial-grade liquid hypochlorite not be diluted and that the smallest pipelines, the flow rate will allow, should be used in the system.

Gas Production

Another concern with commercial-grade hypochlorite is gas production. Hypochlorite loses strength over time and generates oxygen gas as it decomposes. The rate of decomposition increases with concentration, temperature, and metal catalysts.

Personal Safety

A small leakage in the hypochlorite feed lines would result in the evaporation of the water and in turn the release of chlorine gas.

Chlorate Formation

The final area of concern is the possibility of chlorate ion formation. Sodium hypochlorite degrades over time to form the chlorate ion (ClO3-) and oxygen (O2). The degradation of the hypochlorite solution is dependent on the strength of the solution, temperature, and the presence of metal catalysts.

Decomposition of Commercial Sodium Hypochlorite can be created in two major ways:
a). The formation of Chlorates due to high pH, 3NaOCl= 2NaOCl+NaClO3.
b). Chlorine evaporation loss due to temperature increase.

Therefore, for any given strength and temperature, over a period of time, the higher strength product will eventually be lower in available chlorine strength than the lower strength product, since its decomposition rate is greater. The American Water Works Association Research Foundation (AWWARF) concluded that the decomposition of concentrated bleach (NaOCl) is the most probable source of chlorate production. A high concentration of Chlorate is not advisable in drinking water.

Chlorine Comparison Chart

Product Form pH Stability Available Chlorine Form Cl2 gas Low 100% Gas Sodium hypochlorite (Commercial) 13+ 5-10% Liquid Calcium hypochlorite granular 11.5 20% Dry Sodium hypochlorite (On-site) 8.7-9 0.8-1% Liquid

Now, which is the ideal disinfectant?

• Chlorine Gas&#; It is too dangerous to handle and not safe in residential areas. Most of the time, they are not available.
• Bleaching Powder&#; Calcium Hypochlorite is effective, but the whole process of mixing, settling, and disposing of the sludge is very messy and cumbersome. This makes the whole area dirty. Moreover, the bleaching powder absorbs moisture during monsoon or in wet surroundings and emits chlorine gas, making the bleaching power lose its strength.
• Liquid Bleach&#; Liquid Chlorine -or Sodium Hypochlorite is very effective. This is in liquid form so very easy to handle. But the commercially available Liquid Chlorine is not only expensive but loses its strength over a period of time and becomes water. The danger of spillage is a common problem.
• Electro Chlorinator&#;Very effective, economical, safe, and easy to prepare and use. This is the latest technology being adopted in most nations.

Pristine Water offers sodium hypochlorite generator systems that are very effective, budget-friendly, safe, easy to prepare and use.

Our design team will be delighted to create a customized solution for you. Contact us here.

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