Sodium Hydroxide

Sodium Hydroxide - Characteristics and Manufacturing Process of Sodium Hydroxide

Sodium hydroxide comes from carbonate sodium, formerly known as "caustic soda." Sodium carbonate has already been mixed with lime in ancient Egypt to synthesize an alkali: the OH-hydroxide ion in solution with the Na+ sodium ion. Several processes to synthesize it has been developed over the ages, such as the Solvay process in 1861. Today, sodium hydroxide is generated mostly by sodium chloride solution electrolysis.

Sodium hydroxide is also known as Lye, Caustic soda, Alkaline drain cleaner (in solution), Sodium hydrate, Ascarite.

General Characteristics of Sodium hydroxide

  • • Though there is no danger that it will explode or ignite, it reacts with different acids, such as with hydrochloric acid, and is neutralized and generates considerable exothermic neutralization heat.

  • • Metals like aluminum, tin and zinc are corroded. It generates hydrogen during this process, which can act as an explosive gas.

  • • It is highly hygroscopic, absorbing in the air moisture, carbon dioxide, or sulfur dioxide. It is also highly delicate and absorbs humidity to form a watery solution.

  • • When liquid sodium hydroxide is diluted, a significant amount of dilution heat is generated. Because this quickly produces high heat and the resulting solution can spatter if the water is carelessly poured into it, care must be taken.

  • • Sodium hydroxide breaks down animal fibers easily. Despite the decomposition of plant fibers, they have a higher resistance than animal fibers. Although corrosion-resistant materials include stainless steel, steel-epoxy resins and fiber-reinforced plastics, steel, and rubber-lined steel are the most frequently used materials.

  • • A brief of all properties of sodium hydroxide is given in the table below:

  • ParameterCharacteristics
    AppearanceCrystalline solid. Crystalline powder. Little spheres. Lumps. Needles. Scales. Flakes.
    pH14 (5 %)
    Melting point323 °C
    Boiling point1388 °C (1013.25 hPa)
    Vapour pressure< 0.1 hPa (20 °C)
    Relative density2.13 (20 °C)
    Density2130 kg/m³
    Molecular mass40 g/mol
    SolubilityExothermically soluble in water. Soluble in ethanol. Soluble in methanol. Soluble in glycerol.
    Viscosity, kinematic0.53 mm²/s (25 °C, 1 mol/l)
    Viscosity, dynamic0.997 mPa.s (25 °C, Test data)

    Manufacturing Process

    The electrolysis of sodium chloride produces sodium hydroxide and chlorine together. In many parts of the world, there are large deposits of sodium chloride (rock salt). These deposits are nearly pure sodium chloride and are often several hundred meters deep (some up to 3000 meters deep) with 30 to 500 meter thick seams. During the Triassic period, 200 million years ago, they were evaporated from trapped seas. In Europe, for example, the seas produced deposits stretching from Cheshire, Lancashire, Staffordshire, and Cleveland in the UK to Poland, although not continuously. It is also found across the U.S., especially in Louisiana and Texas. A small quantity is mined as rock salt, most are mined by the controlled pumping of water into the salt seam at high pressure. In order to produce dry salt, a proportion of the solution mined brine produced in this way is evaporated. Solar salt is also a source of sodium chloride, produced by the evaporation of seawater by solar heating.

    Saturated brine is purified before electrolysis by adding sodium carbonate, sodium hydroxide, and other reagents to precipitate calcium, magnesium and other harmful cations. Settling and filtration remove the suspended solids from the brine. Today, the three electrolytic processes used. The concentration of caustic soda produced by each process varies:

  • • Membrane Cells: sodium hydroxide is produced as a pure approximately 30 percent (w/w) solution that is normally concentrated by evaporation to a 50 percent (w/w) solution using pressure steam.

  • • Mercury Cells: sodium hydroxide is manufactured as a pure solution of 50 percent (w / w), which is the most commonly sold concentration on the global market. Some are concentrated to 75 percent by evaporation and then heated to 750 - 850 K for solid sodium hydroxide.

  • • Diaphragm Cells: Sodium hydroxide is manufactured as an impure solution called ' diaphragm cell liquor ' (DCL) with typical sodium hydroxide concentrations of 10 - 12 percent (w / w) and sodium chloride of 15 percent (w / w). The DCL must be concentrated using evaporation units that are much larger and more complex than those used on membrane cell plants to produce the required 50 percent (w / w) strength that is usually required. Another aspect of the sodium hydroxide produced in the diaphragm cell is that the product contains a small amount (1 %) of salt as a contaminant that may make the material unsuitable for certain purposes.

  • Uses of sodium hydroxide

    Sodium hydroxide is used in a wide variety of industries, including paper, inorganic chemicals, organic chemicals, aluminum, textiles. A lot is used to scrub gases to remove acids before they are released into the open environment. For example, gasses emitted from the combustion of fossil fuels containing significant amounts of sulfur dioxide. Sulfur dioxide is trapped in many ways, one that is widely used involves scrubbing the gasses with a solution of sodium and calcium hydroxides. This technique is also used in processes of refining, such as bauxite purification.
    Another important use of sodium hydroxide is the production of wood paper. Wood is treated with a solution containing a mixture of sodium sulfide and sodium hydroxide in the most widely used process, the Kraft process. Most of the unwanted material in the wood, such as lignins, dissolves in the liquor, leaving cellulose that is filtered off relatively pure. It is this cellulose that forms the basis of paper after further purification. Other uses include the manufacturing of detergents, soaps, and bleaches, which are usually produced by transferring chlorine gas to a sodium hydroxide solution that generates a sodium chlorate (I) solution (sodium hypochlorite):
    Cl2 (g) + 2 NaOH (aq) NaCl (aq) + NaOCl (aq) + H2O (l)

    Health Hazard

    Ingestion: Corrosive. Swallowing can lead to severe mouth, throat, and stomach burns. It can result in severe tissue scarring and death. There may be similar symptoms of inhalation, severe pain, severe tissue scarring, diarrhea, bleeding, vomiting, blood pressure drop, collapse, and death. Damage can occur days after exposure. Risk of esophagus and stomach perforation.

    Inhalation: Significant irritant. Effects from dust or nebula inhalation vary from mild irritation to severe damage or burning of upper respiratory tract mucous membranes, depending on the severity of exposure. Coughing, wheezing, laryngitis, shortness of breath, nausea, vomiting, sneezing, sore throat, or runny nose may include symptoms. There may be severe chemical pneumonitis and pulmonary edema.

    Skin: Skin corrosive. Skin contact causes severe burns and scarring. Can thoroughly penetrate. Burns are not immediately painful, there may be minutes to hours of pain and irritation.

    Eye: It's corrosive. Causes heavy burns. Can thoroughly penetrate. Ulceration, permanent vision impairment, and permanent blindness may occur in severe cases.

    First-aid measures

    Ingestion: immediately rinse your mouth thoroughly with water. Give drinking water. DO NOT stir up vomiting. If vomiting occurs, to reduce the risk of aspiration, lean the victim forward. If vomiting occurs, provide additional water for effective dilution. Search for immediate medical help.
    Skin: Wash immediately affected areas with abundant amounts of water. Remove and wash contaminated clothes prior to reuse. Search for urgent medical help. Use an emollient to cover the skin.

    Eye Contact: Immediately irrigate for at least 15 minutes with copious amounts of water. Holding eyelids open. Search for immediate medical help. If available, an additional 30 minutes may be used with a neutral saline solution to flush the contaminated eye.

    Handling and storage

    Avoid dust generation or accumulation. Before reuse, contaminated clothes should be removed and washed. It is recommended to apply skin-protective barrier cream. After working with the material, wash hands and face thoroughly. Use away from all sources of ignition in well-ventilated areas. Wear appropriate respiratory equipment in the event of insufficient ventilation. In small quantities, add caustic to water when diluting or preparing a solution to avoid boiling and splattering.

    Environmental Hazard

    The environmental hazard of sodium hydroxide is caused by the ion of hydroxide (pH effect). A high water concentration will lead to toxic effects on aquatic organisms such as fish.


    Sodium hydroxide is used in industrial and consumer products in large quantities. Because of the alkaline properties, high concentrations of sodium hydroxide are corrosive. Direct contact should be avoided with these products. However, when humans are in contact with the substance's non-corrosive and non-irritating concentrations, no effects are expected on human health. In the environment, the substance is neutralized and is therefore not persistent. It is also not accumulating in organisms. Before discharging to the environment, the waste water containing sodium hydroxide should be neutralized (pH control). This prevents effects on the aquatic environment (e.g. organisms that live in a river). By careful using and following the instructions provided, this hazardous substance can be safely used.