147. How is hydrogen peroxide manufactured?

Hydrogen peroxide can be prepared on a large scale by any of the following methods:

1. Electrolytic process. In this process, the electrolysis of 50% sulphuric acid is carried out at low temperature using platinum electrodes and a current of high density. Persulphuric acid is formed.

Persulphuric acid is distilled. Hydrolysis occurs and a distillate containing about 30% H₂O₂ is obtained.

Modification. Recently, it has been observed that if instead of 50% H₂SO₄, an equimolar mixture of H₂SO₄ and ammonium sulphate is electrolyzed, a more concentrated solution of H₂O₂ is obtained.


                  
At anode:

          

At cathode: 
 Ammonium persulphate formed around anode is withdrawn and heated at 43 mm pressure when its hydrolysis occurs forming hydrogen peroxide.

Hydrogen peroxide along with water distills over. Ammonium bisulphate can be used again. This method gives 30-40% aqueous solution of hydrogen peroxide.

2. From 2-ethylanthraquinone. This is the most recent process for the manufacture of hydrogen peroxide. 2-ethyl anthraquinone is catalytically reduced to 2-ethylanthraqinol in an organic solvent by passing hydrogen gas in the presence of palladium (catalyst). The reduced product i.e. 2-ethyl anthraquinol is dissolved in a mixture of benzene and cyclohexanol. On passing air through it, 2-ethylanthraquinone and hydrogen peroxide are formed.

H₂O₂ is extracted with water to give a 20% solution. 2-ethyl anthraquinone is reformed which is again used. The method, thus, involves alternate oxidation and reduction steps.