Caustic soda is a fundamental raw material in the chemical industry with extremely wide applications. In the chemical industry, it is used to produce formic acid, oxalic acid, borax, phenol, soap, synthetic fatty acids, synthetic detergents, and more. In the textile and dyeing industry, it serves as a desizing agent, scouring agent, mercerizing agent, and solvent for vat dyes and Hydron Blue dyes. In the metallurgical industry, it is used to manufacture alumina and metal surface treatment agents. In the instrument industry, it functions as an acid neutralizer, decolorizing agent, and deodorizing agent. In the adhesive industry, it is used as a starch gelatinizing agent and neutralizer. Additionally, it finds extensive applications in industries such as enamel, pharmaceuticals, cosmetics, leather, coatings, pesticides, and glass.
I. Refining Petroleum
After petroleum products are washed with sulfuric acid, they still contain some acidic substances that must be washed with a sodium hydroxide solution, followed by water washing, to obtain refined products.
II. Dyeing
III. Textile Fibers
IV. Papermaking
V. Soil Improvement with Lime
VI. Chemical Industry and Chemical Reagents
1. Pharmaceuticals
Stomach medicine: Ingredients include aluminum hydroxide, magnesium hydroxide, sodium bicarbonate, and a small amount of sodium hydroxide, primarily to neutralize stomach acid.
Sodium carboxymethyl cellulose (CMC): Used for emulsification, adhesion, and film formation in food and pharmaceuticals. In detergents, it acts as an anti-soil redeposition agent. It is produced by reacting refined cotton with NaOH to form alkali cellulose, followed by a one-step etherification reaction with chloroacetic acid.

2. Green Water Treatment Agents
Preparation of Sodium Ferrate (Na2FeO4)
3NaClO (bleach) + 2Fe(OH)3 (ferric hydroxide) + 4NaOH == 2Na2FeO4 + 3NaCl + 5H2O
Basic aluminum chloride (PAC/BAC) denatures viral proteins and is used for water purification and wastewater treatment, with strong sodium oxide adjusting pH.
3. Ion Exchange Resins
After anion exchange resins are exhausted, they are generally regenerated with a 5%-8% NaOH solution.
4. Alkaline Cleaning Agents
NaOH solution can be used in various cleaning agents, such as car wash liquids, bottle cleaners, dishwashing detergents, rust removers, and disinfectants. It is mainly used for cleaning bottles in the wine-making industry and for surface treatment in the ceramic and metal industries.
5. Bleach and Bleaching Agents
VII. Rubber and Leather
1. Precipitated Silica
2. Recycling of Old Rubber
In the recycling of old rubber, rubber powder is pretreated with a sodium hydroxide solution before subsequent processing.
3. Leather
VIII. Metallurgy, Electroplating
IX. Other Applications
1. Ceramics: Caustic soda serves two purposes in ceramic manufacturing. First, it acts as a diluent during the firing process. Second, after firing, ceramic surfaces may have scratches or roughness, which can be smoothed by washing with a caustic soda solution.
2. In the instrument industry, it is used as an acid neutralizer, decolorizing agent, and deodorizer.