CHLORINE, CHLORIDE OF CALCIUM, AND CHLORATES
Manufacture.—The older processes depend on the preparation of chlorine and hydrochloric acid by an oxidation process in which the oxidising agent is either a compound rich in oxygen—usually common manganese dioxide (pyrolusite)—or the oxygen of the air in the presence of heated copper chloride (as catalytic agent). The former (Weldon process) is less used now than either the latter (Deacon process) or the electrolytic manufacture of chlorine.
In the Weldon process from the still liquors containing manganous chloride the manganese peroxide is regenerated, and this so regenerated Weldon mud, when mixed with fresh manganese dioxide, is used to initiate the process. This is carried out according to the equations:
- MnO₂ + 4HCl = MnCl₄ + 2H₂O
- MnCl₄ = MnCl₂ + Cl₂.
Fig. 6.—Preparation of Chlorine—Diaphragm Method (after Ost)
Hydrochloric acid is first introduced into the chlorine still (vessels about 3 m. in height, of Yorkshire flag or fireclay), next the Weldon mud gradually, and finally steam to bring the whole to boiling; chlorine comes off in a uniform stream. The manganous chloride still liquor is run into settling tanks. The regeneration of the manganous chloride liquor takes place in an oxidiser which consists of a vertical iron cylinder in which air is blown into the heated mixture of manganous chloride and milk of lime. The dark precipitate so formed, ‘Weldon mud,’ as described, is used over again, while the calcium chloride liquor runs away.
The Deacon process depends mainly on leading the stream of hydrochloric acid gas evolved from a saltcake pot mixed with air and heated into a tower containing broken bricks of the size of a nut saturated with copper chloride. Chlorine is evolved according to the equation:
- 2HCl + O = 2Cl + H₂O.
