Chlorine dioxide production using mixed hydrochloric and sulfuric acid feed

A process for the production of chlorine dioxide, which comprises

• reacting sodium chlorate with chloride ions and hydrogen ions in an aqueous acid reaction medium having a total acid normality of about 2 to about 4.8 normal to form chlorine dioxide and chlorine, said chloride ions being provided by hydrochloric acid alone or hydrochloric acid and sodium chloride and said hydrogen ions being provided by sulphuric acid and said hydrochloric acid,
• maintaining said reaction medium at its boiling point at a temperature below that above which substantial decomposition of chlorine dioxide occurs while applying a subatmospheric pressure to a first reaction zone containing said reaction medium to form steam in a volume ratio of steam to chlorine dioxide of about 4:1 to about 10:1,
• depositing anhydrous neutral sodium sulphate from the reaction medium and removing the same from said first reaction zone,
• removing a gaseous mixture of chlorine dioxide, chlorine and steam from said first reaction zone and forming an aqueous solution of said chlorine dioxide and a gaseous chlorine stream therefrom, said aqueous solution of chlorine dioxide also containing part of said chlorine in said gaseous mixture,
• forwarding the chlorine not dissolved in said chlorine dioxide solution to a second reaction zone to which sulphur dioxide and water are fed for reaction therein to form an aqueous mixture of hydrochloric acid and sulphuric acid having a total acid normality of about 6 to about 14 normal,
• cooling said second reaction zone to maintain the temperature of the reactants therein at a temperature below the boiling point of water,
• said cooling being achieved, at least in part, by effecting said reaction of sulphur dioxide, chlorine and water in a cooled falling film absorber in which the water forms the falling film and having integral cooling passages through which a cool heat exchange medium flows out of fluid flow communication with but in heat exchange communication with the falling film and
• forwarding said aqueous mixture of hydrochloric acid and sulphuric acid and sulphuric acid to said reaction medium and feeding such additional quantities of hydrogen ions, chloride ions and sulphate ions to said reaction medium as are required by the stoichiometry of the reactions occurring in the reaction medium.

A method for the production of hydrochloric acid and sulphuric acid, which comprises:

• separately feeding chlorine, sulphur dioxide and water to a reaction zone,
• intimately contacting said chlorine, sulphur dioxide and water to cause the same to react in the presence of excess water in accordance with the equation:
• SO.sub.2 +Cl.sub.2 +2H.sub.2 O.fwdarw.2HCl+H.sub.2 SO.sub.4
• to form an aqueous mixture of hydrochloric acid and sulphuric acid, and
• cooling said reaction zone sufficiently to maintain the reactants in said reaction zone at a temperature below the boiling point of water during said reaction,
• said reacton zone being defined at least in part by a falling film absorber in which the water forms the falling film and at least the majority of the sulphur dioxide and chlorine react and having integral cooling passages through which said cool heat exchange medium flows out of fluid flow contact with but in heat conducting relationship with said falling film.

A method for the production of hydrochloric acid and sulphuric acid, which comprises:

• separately feeding chlorine, sulphur dioxide and water to a reaction zone,
• intimately contacting said chlorine, sulphur dioxide and water to cause the same to react in the presence of excess water in accordance with the equation:
• SO.sub.2 +Cl.sub.2 +2H.sub.2 O.fwdarw.2HCl+H.sub.2 SO.sub.4
• to form an aqueous mixture of hydrochloric acid and sulphuric acid, and
• cooling said reaction zone sufficiently to maintain the reactants in said reaction zone at a temperature below the boiling point of water during said reaction,
• said reaction zone being defined by a packed tower, to which said chlorine and sulphur dioxide are directly fed and to which said water is fed in admixture with cooled recycled mixed acid, a hot mixed acid stream of hydrochloric acid and sulphuric acid is removed from the packed tower and passed through a heat exchanger to which a cool heat exchange medium also is passed in order to cool the hot mixed acid, a proportion of the cooled mixed acid is recovered as a product stream, and the remainder of the cooled mixed acid is recycled to the reaction zone in said admixture with said water.

A process for the production of chlorine dioxide, which comprises:

• reacting sodium chlorate with chloride ions and hydrogen ions in an aqueous acid reaction medium having a total acid normality of about 2 to about 4.8 normal to form chlorine dioxide and chlorine, said chloride ions being provided by hydrochloric acid alone or hydrochloric acid and sodium chloride and said hydrogen ions being provided by sulphuric acid and said hydrochloric acid,
• maintaining said reaction medium at its boiling point at a temperature below that above which substantial decomposition of chlorine dioxide occurs while applying a subatmospheric pressure to a first reaction zone containing said reaction medium to form steam in a volume ratio of steam to chlorine dioxide of about 4:1 to about 10:1,
• depositing anhydrous neutral sodium sulphate from the reaction medium and removing the same from said first reaction zone,
• removing a gaseous mixture of chlorine dioxide, chlorine and steam from said first reaction zone and forming an aqueous solution of said chlorine dioxide and a gaseous chlorine stream therefrom, said aqueous solution of chlorine dioxide also containing part of said chlorine in said gaseous mixture,
• forwarding the chlorine not dissolved in said chlorine dioxide solution to a second reaction zone to which sulphur dioxide and water are fed for reaction therein to form an aqueous mixture of hydrochloric acid and sulphuric acid having a total acid normality of about 6 to about 14 normal,
• cooling said second reaction zone to maintain the temperature of the reactants therein at a temperature below the boiling point of water,
• said cooling being achieved by effecting said reaction of sulphur dioxide, chlorine and water in a packed tower, passing hot mixed acid produced therein through an external heat exchanger to which a cool heat exchange medium is passed, recovering part of the cool mixed acid forwarded to said reaction zone, and mixing the remainder of the cool mixed acid with said water for forwarding to said packed tower, and
• forwarding said aqueous mixture of hydrochloric acid and sulphuric acid and sulphuric acid to said reaction medium and feeding such additional quantities of hydrogen ions, chloride ions and sulphate ions to said reaction medium as are required by the stoichiometry of the reactions occurring in the reaction medium.