Caustic soda also known as sodium hydroxide Sodium hydroxide (NaOH) is widely used. It is used to produce paper, soap, dyestuff, rayon, smelting metal, petroleum refining, cotton fabric finishing, purification of coal tar products, and food processing, wood processing and machinery industry.
It can be used as a chemical experiment. In addition to being used as a reagent, it can also be used as an alkaline desiccant because of its strong water absorption and deliquescence.  Acidic gases can also be absorbed (e.g. in the experiment of sulfur burning in oxygen, sodium hydroxide solution can be packed into bottles to absorb toxic sulfur dioxide).
Sodium hydroxide is widely used in the national economy, and many industrial sectors require sodium hydroxide. The sectors that use sodium hydroxide most are chemicals, followed by paper, aluminum, tungsten, rayon, cotton and soap. In addition, in the production of dyes, plastics, chemicals and organic intermediates, the regeneration of old rubber, the production of metal sodium, water electrolysis, and the production of inorganic salts, the production of borax, chromate, manganate, phosphate and so on, and a large amount of caustic soda should also be used. At the same time, sodium hydroxide is one of the important raw materials for the production of polycarbonate, super absorptive polymer, zeolite, epoxy resin, sodium phosphate, sodium sulfite and a large amount of sodium salt.
Soap: making soap is the oldest and most widely used caustic soda.
Sodium hydroxide has been used in traditional life. To date, the demand for caustic soda in soap, soap and other kinds of washing products still accounts for about 15% of caustic soda. Detergent: sodium hydroxide is used to produce a variety of detergents, and even today's detergent (twelve alkyl benzene sulfonate components) is also made from a large number of caustic soda. The caustic soda is used for sulfation of excess smoke after the sulfonation reaction.
Sodium hydroxide plays an important role in the paper industry. Because of its basic characteristics, it is used in the process of boiling and bleaching paper.
Papermaking materials are wood or grass plants, these plants in addition to cellulose, but also contains a considerable number of non-cellulose (lignin, gum, etc.). The non-cellulose components can be dissolved and separated by adding dilute sodium hydroxide solution, and the pulp with cellulose as the main component can be prepared.
Artificial fiber and textile
Artificial fibers, such as artificial cotton, artificial wool, rayon, etc., are mostly viscose fibers, they are made of cellulose, sodium hydroxide, carbon disulfide (CS2) as raw materials for viscose liquid, made by spraying silk and condensing.
In the textile industry, sodium hydroxide is used for fiber treatment and dyeing, and is used for mercerizing cotton fibers. After treating cotton fabric with caustic soda solution, it can remove the wax, grease and starch covering the cotton fabric, and increase the mercerizing color of the fabric to make the dyeing more uniform.
Petroleum products after washing with sulfuric acid also contain some acidic substances, must be washed with sodium hydroxide solution, and then washed with water, can be refined products.
China's "Hygienic Standard for the Use of Food Additives" (GB 2920-1996) stipulates that: it can be used as processing aids, according to the production needs of appropriate use.
Sodium hydroxide can be widely used in the following production processes: the cleaning process of the container; the processing of starch; the preparation of carboxymethyl cellulose; the manufacturing process of sodium glutamate.
Sodium hydroxide is widely used in water treatment. In sewage treatment plants, sodium hydroxide can reduce the hardness of water by neutralization reaction. In the industrial field, it is a regeneration agent for ion exchange resin regeneration. Sodium hydroxide is strongly alkaline and has relatively high solubility in water. Sodium hydroxide in water has a relatively high solubility, so it is easy to measure the amount of water, can be easily used in various fields of water treatment.
Sodium hydroxide is used in water treatment as follows: to eliminate the hardness of water; to regulate the pH value of water; to neutralize the wastewater; to remove heavy metal ions in water by precipitation; and to regenerate the ion exchange resin.
Sodium hydroxide is used to treat bauxite, alumina is contained in bauxite and alumina is the raw material for the production of aluminum. Sodium hydroxide can be used to purify alumina from the concentrate.