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Industrial use

Industrial use

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  • 1. The industry use of sodium hydroxide: Sodium hydroxide, also sometimes called lye, is a corrosive substance and because of this property, it is widely used in industry for soap making, as a cleaning agent, in aluminum production and for paper pulping. Soap making: Sodium hydroxide is used to produce soap; the common fats, triglyceride esters react with sodium hydroxide to form glycerol and the sodium salt of the fatty acid which is soap. The reaction between a strong base and a fat is called ‘saponification’, and can be represented by the following chemical reaction between olive oil and sodium hydroxide: http://www.digipac.ca/chemical/mtom/contents/chapter3/making_soap.htm The equation can be simplified to C18H36O2 + NaOH = alcohol + salt of the carboxylic acid (soap) Cleaning agent: For the same theory of soap making, in industry, sodium hydroxide can be used as cleaning agent and it is called ‘caustic’. Sodium hydroxide is usually added to hot water and then can be used to dissolve fat, grease, oil and protein based deposits. This is why sodium hydroxide is often contained in oven cleaners. Sodium hydroxide solution is widely used in cleaning the oil which is used in making
  • 2. metal products. Compared to CFC (chlorofluorocarbon, a powerful substance to clean the oil), it does not pollute the environment. The industrial oil does not react easily, so it needs energy to break it up to react; the hot water provides the energy required to make the sodium hydroxide work efficiently. Aluminum production: Aluminium ore is usually contained in the mineral bauxite that is a mixture of hydrated aluminium oxides Al2O3 and hydrated iron oxides, Fe2O3. In aluminum refining, sodium hydroxide takes the job of separating the aluminium oxides and other substances in the ore. The process is called ‘Bayer Process’ and it produces pure alumina from bauxite. In the process, the sodium hydroxide will only react with aluminium oxide and form sodium aluminates, NaAl(OH)4 which are in solution, and after filtration, the iron oxide and other substances will be separated. The ironic equation will be: Al2O3(s) + 2 OH−(aq) + 3 H2O(l) → 2 [Al(OH)4] (aq)− The equation with NaOH: Al2O3(s) + 3H2O(l) + 2NaOH(aq) -----> 2NaAl(OH)4(aq) After that, aluminum oxide will precipitate due to the introduction of the aluminum hydroxide and then the precipitates are washed and heated to form pure aluminum.
  • 3. http://www.emt-india.net/process/aluminium/Aluminum%20flowsheet.htm Cryolite, Na3AlF6 Production: Cryolite is a useful material that is used in the production of potassium aluminium sulphate, sodium carbonate and aluminium sulphate. To produce this material, aluminium oxide, hydrogen fluoride and sodium hydroxide are required. With the similar equation as aluminium production: Al2O3 + 2NaOH = 2NaAlO2 (Aluminate) + H2O 6HF + 3NaAlO2 = Na3AlF6 (Cryolite) + 2Al(OH)3
  • 4. http://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Cryolite.jpg/220px-Cryolite.jpg Paper pulp industry: In the process of paper making, there are two main parts: pulping and papermaking. Pulping is a process of delignification-removing lignin from wood while leaving cellulose fibers intact.1 In paper pulp industry, a chemical method is usually selected. After breaking all the fibers apart, an amount of water is added to form a mixture of 95% water and 5% fibers which is then transferred to the paper machine to produce paper. There are always some excess chemicals used to pulp the paper, sodium hydroxide will help regenerate these chemicals to reduce the cost. Because of the corrosive property of sodium hydroxide, it will also be added to the process of bleaching to increasing the efficiency. It also has a function of PH control. During the pulp process, sodium hydroxide helps the PH stays at around 8 where the hypochlorite bleach works the most efficiently. Cl2 + H2O ⇌ H+ + Cl- + HClO ‘At pH > 8 the dominant species is hypochlorite, ClO-, which is also useful for lignin removal. Sodium hypochlorite can be purchased or generated in situ by reacting chlorine with sodium hydroxide.’2 2 NaOH + Cl2 ⇌ NaOCl + NaCl + H2O Sodium hydroxide is also used in paper recycling. When the wasted paper is placed
  • 5. into the sodium hydroxide solution, the paper will swell and that helps to remove the ink. http://dsp-psd.pwgsc.gc.ca/Collection-R/LoPBdP/BP/bp292-e.htm http://www.madehow.com/Volume-2/Paper.html