What are the uses of caustic soda

Caustic soda is a kind of caustic soda. Its chemical name is sodium hydroxide. It is a strong soluble alkali and is extremely corrosive. Peeling agents, detergents, etc., are widely used. The common uses of caustic soda are summarized below:

1. Papermaking: The raw materials for papermaking are wood or grass plants. In addition to cellulose, these plants also contain a considerable amount of non-cellulose (lignin, gum, etc.). Caustic soda is used for delignification, and only when the lignin in the wood is removed can fibers be obtained. Adding dilute caustic soda solution can dissolve and separate the non-cellulose components, so as to make pulp with cellulose as the main component.

2. Refined petroleum: After being washed with sulfuric acid, petroleum products still contain some acidic substances, which must be washed with caustic soda solution, and then washed with water to obtain refined products.

3. Textile: Cotton and linen fabrics are treated with concentrated sodium hydroxide (caustic soda) solution to improve fiber properties. Man-made fibers such as artificial cotton, artificial wool, artificial silk, etc., are mostly viscose fibers. They are made of cellulose (such as pulp), caustic soda, and carbon disulfide (CS2) as raw materials to make viscose liquid, which is sprayed and coagulated. And made.

4. Printing and dyeing: After the cotton fabric is treated with caustic soda solution, it can remove the wax, grease, starch and other substances covered on the cotton fabric, and at the same time, it can increase the mercerized color of the fabric and make the dyeing more uniform.

5. Manufacture of soap: The main component of soap is the sodium salt of higher fatty acid, which is usually made from oil and caustic soda through saponification reaction. In addition to high-grade fatty acid salts, soap also contains fillers such as rosin, water glass, spices, and dyes. From the structural point of view, the molecule of higher fatty acid sodium contains non-polar hydrophobic part (hydrocarbon group) and polar hydrophilic part (carboxyl group). Hydrophobic groups have lipophilic properties. When washing, the grease in the dirt is stirred and dispersed into fine oil droplets. After contacting with soap, the hydrophobic group (hydrocarbon group) of the higher fatty acid sodium molecules is inserted into the oil droplets, and the oil molecules are combined by van der Waals force. The hydrophilic group (carboxyl group) which is easily soluble in water extends out of the oil drop and inserts into the water. The main ingredient of soap is NaOH, but NaOH is not soap. Its aqueous solution has a creamy feel and can be used to make soap. Soap is an emulsifier. The principle is the saponification reaction CH3COOCH2CH3+NaOH=CH3COONa+CH3CH2OH, CH3COONa is the active ingredient in soap.

6. Chemical industry: Caustic soda is used in the manufacture of sodium metal and electrolysis of water. The production of many inorganic salts, especially the preparation of some sodium salts (such as borax, sodium silicate, sodium phosphate, sodium dichromate, sodium sulfite, etc.) must use caustic soda. Caustic soda is also used in the synthesis of dyes, drugs and organic intermediates.

7. Metallurgical industry: It is often necessary to convert the active ingredients in the ore into soluble sodium salts in order to remove insoluble impurities. Therefore, it is often necessary to add caustic soda. For example, in the smelting process of aluminum, caustic soda is used in the preparation of cryolite and the treatment of bauxite.

8. Use lime to improve the soil. In the soil, organic acids will be generated during the decomposition of organic matter, and acidic substances may also be produced by the weathering of minerals. In addition, the use of inorganic fertilizers such as ammonium sulfate and ammonium chloride will also make the soil acidic. Applying an appropriate amount of lime can neutralize the acidic substances in the soil, making the soil suitable for crop growth and promoting the reproduction of microorganisms. The increase of Ca2+ in the soil can promote the coagulation of soil colloids, which is conducive to the formation of aggregates, and at the same time can supply the calcium needed for plant growth.

9. Alumina production: NaOH solution is heated to dissolve alumina in bauxite to obtain sodium aluminate solution. After the solution is separated from the residue (red mud), lower the temperature, add aluminum hydroxide as a seed crystal, stir for a long time, the sodium aluminate decomposes and separates aluminum hydroxide, washes it, and calcines it at a temperature of 950-1200°C, and then Alumina products are obtained. The solution after the precipitation of aluminum hydroxide is called mother liquor, which can be recycled after evaporation and concentration. Due to the different crystal structures of gibbsite, boehmite and diaspore, their solubility in caustic soda solution is very different, so different dissolution conditions should be provided, mainly different dissolution temperatures. Gibbsite-type bauxite can be dissolved at 125-140°C, and diaspore-type bauxite should be dissolved at 240-260°C with lime (3-7%) added.

10. Ceramics: Caustic soda plays two roles in ceramic manufacturing: first, caustic soda acts as a diluent during the firing process of ceramics. Second, the fired ceramic surface will be scratched or very rough. After cleaning with caustic soda solution, the ceramic surface will be smoother.

11. Disinfection: Denature the protein of the virus. These are mainly used in the cleaning and disinfection of bottles in the wine industry.

12. Wastewater removal: strong sodium oxide adjusts the ph value, treats sewage, and recycles resources.

13. Chemical preparations, industrial additives. Caustic soda is mainly used in the pharmaceutical industry to alkalize the solution or adjust the pH value of the liquid.

14. Electroplating and tungsten refining. Caustic soda is used as an electroplating solution in metal plating and acts as a conductor!

15. Manufacture silk and rayon.

16. Leather industry

17. Detergent chemical industry, used to manufacture formic acid, oxalic acid, borax, phenol, sodium cyanide and soap, synthetic fatty acid, synthetic detergent, etc.

18. In the textile printing and dyeing industry, it is used as a solvent for cotton desizing agent, scouring agent, mercerizing agent, vat dye and Haichang blue dye.

19. In the smelting industry, it is used to manufacture aluminum hydroxide, aluminum oxide and metal surface treatment agents.

20. In the instrument industry, it is used as an acid neutralizer, decolorizer, and deodorizer.

21. Adhesive industry, used as starch gelatinizer and neutralizer.

22. Manufacture of phosphate and manganate.

23. Regeneration of old rubber.

24. It can be used as peeling agent, decolorizing agent and deodorizing agent for citrus and peach.

25. Caustic soda is also used in the manufacture of pesticides.