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        Method for preparing sodium hydroxide

        TIME:2019-01-25 

          Sodium salt reacts with calcium oxide

          Some sodium bicarbonate (sodium bicarbonate) and some calcium oxide (lime) can be used. Put the quicklime in water, and then turn into lime slurry (calcium hydroxide solution, slaked lime), and add solid particles of sodium bicarbonate (or sodium carbonate) (concentrated solution) to the lime slurry to ensure the product sodium hydroxide. The purity required to pass the lime slurry. Reason: Refer to the solubility of calcium hydroxide and sodium carbonate. Stir and accelerate the reaction. After the reaction for a while, let stand for a while. With the precipitation of calcium carbonate, the supernatant liquid is sodium hydroxide solution, and it can be poured out carefully. (Remember that you can't put it on the filter paper when you put it out after weighing!)

          CaO + H2O = Ca(OH)2

          NaHCO3+ Ca(OH)2=CaCO3↓+ NaOH + H2O (recommended)

          Ca(OH)2+Na2CO3 =CaCO3↓+2NaOH

          Sodium reacts with water

          Take a piece of sodium metal, wipe off the surface kerosene, scrape off the surface oxide layer, and place it in a beaker filled with water.

          2Na+2H2O=2NaOH+H2↑

          Phenomenon: (floating, melting, swimming, ringing)

          Floating: sodium floats on the water;

          Melting: sodium is melted into small balls;

          Swim: Sodium moves upstream of the water surface because of hydrogen generation;

          Ringing: Sodium sizzles because there is hydrogen generated.

          Industrial law

          Industrial methods for producing caustic soda are three methods: causticization, electrolysis, and ion exchange membrane.

          Caustic method

          The soda ash and the lime are separately made into a soda ash solution and lime to make a lime milk, and the causticizing reaction is carried out at 99 to 101 ° C. The causticizing solution is clarified and concentrated by evaporation to 40% or more to prepare a liquid caustic soda. The concentrate is further concentrated and solidified to obtain a solid caustic soda product. The caustic mud is washed with water and the wash water is used for alkali.

          Na2CO3+Ca(OH)2= 2NaOH+CaCO3↓

          Diaphragm electrolysis

          After the original salted salt is added to the soda ash, caustic soda, cerium chloride refined preparation to remove impurities such as calcium, magnesium, sulfate ions, and then added sodium polyacrylate or caustic bran in the clarification tank to accelerate precipitation, sand filtration and then added to hydrochloric acid And, the brine is sent to the electrolysis after preheating, and the electrolyte is preheated, evaporated, separated into salts, and cooled to obtain a liquid caustic soda, and further concentrated to obtain a solid caustic soda product. Salt mud wash water is used to make salt.

          2NaCl+2H2O[electrolysis] = 2NaOH+Cl2↑+H2↑

          Ion exchange membrane method

          After the original salted salt is refined according to the traditional method, the primary brine is filtered through a microporous sintered carbon tube filter, and then subjected to secondary refining through a chelating ion exchange resin column to make calcium and magnesium in the brine. The content is reduced to below 0.002%, the secondary refined brine is electrolyzed, chlorine gas is generated in the anode chamber, Na+ in the anode chamber brine enters the OH of the cathode chamber and the cathode chamber through the ion membrane to form sodium hydroxide, and H+ is directly discharged on the cathode to generate hydrogen gas. . During the electrolysis process, an appropriate amount of high-purity hydrochloric acid is added to the anode chamber to neutralize the returned OH-, and the desired pure water should be added to the cathode chamber. The high-purity caustic soda produced in the cathode chamber has a concentration of 30% to 32% by mass, and can be directly used as a liquid alkali product, or can be further concentrated to obtain a solid caustic soda product.

          2NaCl+2H2O= 2NaOH+H2↑+Cl2↑


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