Caustic Soda – A Basic Chemical with Versatile Applications

May 22, 2020

Caustic Soda also known as sodium hydroxide is a basic product that is widely used in a diverse range of industrial sectors, either as a raw material or as an auxiliary chemical. It is commercially sold in two forms: the first one is a solution (diluted) also known as lye, with various concentrations usually in the 30-32% & 48-50% range, and the second one is in the solid form as flakes or Prills (pearls)/granules. The different types of forms do not change the outcome of what you are trying to do. Having said that it has a diverse range of applications, let us look at the major applications of caustic soda in detail:

Applications of Caustic Soda in different industries: 

1) Soap & Detergent Industry – Saponification process is the heart of Soap-Making. It is the chemical reaction in which the building blocks of fats and oils (triglycerides) react with aqueous caustic to form Soap. Soaps are therefore nothing but sodium salts of long chain fatty acids. Detergent manufacturers use caustic as neutralizer to neutralize the access oleum present after the sulphonation reaction of LAB in LABSA.

2) Textile & Fibre Production – Caustic soda is widely used in the textile industry for processes such as scouring, mercerization and dyeing, which are the integral parts of the textile manufacturing process.

  • Scouring is a chemical washing process used to remove unwanted materials from the cotton fabric. In this process, the fabric is boiled in an alkaline solution made up of caustic soda. The caustic soda forms a soap with the free fatty acids through a process called Saponification to remove natural wax, oil and other impurities such as the remaining seed fragments in the fabric. This process is usually a prerequisite to most finishing processes within the textile industry.

  • Caustic soda is also used in mercerizing, a process used to increase the strength, luster and dye affinity of the fabric. In this process, caustic soda is added to the fabric to cause swelling of the fibres which in turn enhances the properties of the fabric. The fabric is usually mercerized under tension to reduce shrinkage, a common occurrence during the mercerizing process.

  • Caustic soda is used in textile dyeing as most dyeing processes require a controlled pH level. Hence, caustic soda is added into the solution to maintain the pH levels during dyeing processes. 

3) Pulp & Paper Industry – In the chemical pulping process, caustic soda in the form of lye is usually used to remove the lignin that binds the fibers. Caustic soda is also used is in paper recycling. The sodium hydroxide causes the fibers to swell when they are placed in a solution with the sodium hydroxide. This swelling helps to separate the ink that is attached to the fibers allowing the fibers to be reused.

4) Refining of Edible Oil - Refining vegetable oils also calls for this product to be used as a neutralizer to rid them of free fatty acids that can give oils an unpleasant taste.

5) Petroleum Processing (refineries) – Caustic soda is used as alkalinity sources in the liquid scrubbing of Sulphur dioxide in flue gases produced from crude-oil-fired steam generators used in thermally enhanced oil recovery. Caustic soda allows the SO2 scrubber to run at a lower pH with a higher SO2 removal capacity. This process is known as desulfurization.

6) Mining and refining (Aluminum production) - Alumina is produced from bauxite, an ore that is mined from topsoil in various tropical and subtropical regions using The Bayer process. After the bauxite is crushed, washed and dried, it is dissolved with caustic soda at high temperatures to extract alumina in the form of sodium aluminate which then goes through multi stage process to form Aluminum .

7) Water treatment - In water treatment, caustic is a powerful means for pH adjustment & neutralizing water streams. Caustic soda is sometimes used during water treatment to raise the pH of water supplies. Increased pH makes the water less corrosive to plumbing and reduces the amount of lead, copper and other toxic metals that can dissolve into drinking water. It is also used for regeneration of anion resin in ion-exchanger during demineralization process.

8) Cleaning agent – Caustic soda is frequently used as an industrial cleaning agent especially for cleaning and sterilizing of bottles in beverage industry. It is added to water, heated, and then used to clean process equipment, storage tanks, etc. It can dissolve oils, fats and protein based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties.

9) As a reagent In chemical processing - Caustic soda serves as a reactive agent in the production process, delivering sodium to the final product in various ways and for many different purposes. Caustic soda is for example used in the production of silica’s, silicates and meta-silicates, phosphates, fibres, bleach, as well as in food processing (for example of sugar) and in the refining of vegetable and mineral oils. 

In a Nutshell, Caustic soda has a lot many applications and is a vital part of many chemical industries and hence it is a product that is consumed in very high quantity world-wide. Many of the readers might be wondering that if the applications are same for all the forms of caustic, why some industries prefer prills over flakes paying higher price. Well we are here to help and break it down easier for you by dedicating a separate blog specially catering this topic shortly.

Disclaimer: The information contained above is for general guidance or matters of interest only. The application and impact laws can vary widely based on the specific facts involved. While we have made every attempt to ensure that the information shared is accurate and has been obtained from personal interactions with Industry experts as well as other secondary reliable sources.

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