Sodium hydroxide - Industrial use

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