Process and a device for the production of chlorine dioxide

A process for the continuous production of chlorine dioxide wherein

• (a) an alkali metal chlorate solution containing alkali chloride is reacted with hydrochloric acid to form a gaseous mixture of ClO.sub.2 and Cl.sub.2 and an alkali metal chloride solution depleted of chlorate, in a cascade reactor under an underpressure of 0.2 to 0.3 bar at the outlet of the cascade reactor, and a flow of air is introduced into the reactor to maintain a partial pressure of ClO.sub.2 not exceeding 0.15 bar,
• (b) the gaseous mixture is passed into a separation column where ClO.sub.2 is washed out with water to form a solution of ClO.sub.2, and
• (c) the Cl.sub.2 remaining after ClO.sub.2 has been washed out of the gaseous mixture is reacted in an HCl synthesis furnace with hydrogen cathodically-formed in a chlorate-electrolysis plant, along with externally produced Cl.sub.2, to give hydrochloric acid and the hydrochloric acid is introduced into the cascade reactor,
• (d) the alkali metal chloride solution depleted of chlorate is withdrawn from the outlet of the reactor and introduced into the chlorate-electrolysis plant forming chlorate and hydrogen therefrom, the chlorate solution is then recycled into the reactor and the hydrogen is introduced into the HCl-synthesis furnace.