Production of chlorine dioxide

Claim 1

In a process for continuously generating a mixture containing chlorine dioxide, chlorine and sulfate wherein a. an alkali metal chlorate, an alkali metal chloride and sulfuric acid are continuously reacted in a single vessel generator-evaporator-crystallizer in proportions to generate chlorine dioxide, chlorine and alkali metal sulfate, in the absence of a catalyst; b. the temperature is maintained at from about 65° to about 85° centigrade; c. the acidity of the reaction solution is maintained at from above 4 to about 11 normal; d. the reaction solution is subjected to a vacuum of from about 100 to about 400 millimeters of mercury absolute to effect evaporation of water vapor; e. chlorine dioxide and chlorine produced by said reaction is withdrawn in admixture with said water vapor; and f. alkali metal acid sulfate is continuously crystallized within said single vessel generator-evaporator-crystallizer and continuously withdrawn therefrom; the improvement which comprises continuously passing the alkali metal acid sulfate crystals produced in said single vessel generator-evaporator-crystallizer in the form of a slurry into the top of a metathesis column, in a downward flow; countercurrently passing a stream of dilute hydrochloric acid upwardly through said column at a rate and in amounts sufficient to effect reaction with said alkali metal acid sulfate, converting said alkali metal acid sulfate to sulfuric acid and alkali metal chloride, continuously returning the sulfuric acid and chlorate values substantially completely to said single vessel generator-evaporator-crystallizer; and continuously removing alkali metal chloride slurry from the bottom of said metathesis column.