Erco Industries Limited

Tenneco Canada Inc.

Sterling Canada, Inc.

Maurice C Fredette

Richard Swindells

Edward J Bechberger

Herbert C Scribner

Marek Lipsztajn

Zbigniew Twardowski

W Howard Rapson

Ching-Shi Yang

Gerald Cowley

Chunmin Pu

Norman W Meyers

Michael S Zell

Sodium sesquisulfate produced in crystalline form in a high acidity highly efficient chlorine dioxide generating process is converted by metathesis to crystalline anhydrous neutral sodium sulfate and the acid recovered as a result is recycled to the chlorine dioxide generating step. The metathesis is effected by contacting the crystalline sodium sesquisulfate with aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol or water alone. The metathesis is effected in such manner as to minimize the additional evaporative load imposed on the chlorine dioxide generating process by the metathesis medium.

Metathesis of acidic by-product of chlorine dioxide generating process

Chlorine dioxide, useful as a pulp mill chemical, is produced without producing sodium sulfate effluent for disposal, by effecting reduction of chloric acid in an aqueous reaction medium in a reaction zone at a total acid normality of up to about 7 normal in the substantial absence of sulfate ion and in the promence of a dead load of sodium chlorate added to and subsequently removed from the reaction medium. Chloric acid for the process is produced electrolytically from an aqueous solution of the deadload sodium chlorate and make-up quantities of sodium chlorate. The chloric acid reduction to produce chlorine dioxide may be effected using methanol or electrolytically.

Chlorine dioxide generation from chloric acid

Sodium sesquisulfate produced in crystalline form in a high acidity methanol-based highly efficient chlorine dioxide generating process is converted by metathesis to crystalline anhydrous neutral sodium sulfate and the acid recovered as a result is recycled to the chlorine dioxide generating step. The metathesis is effected by contacting the crystalline sodium sesquisulfate with aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol or water alone. The metathesis is effected in such manner as to minimize the additional evaporative load imposed on the chlorine dioxide generating process by the metathesis medium.

Metathesis of acidic by-product of chlorine dioxide generating apparatus

Chlorine dioxide, useful as a pulp mill chemical, is produced without producing sodium sulfate effluent for disposal, by effecting reduction of chloric acid in an aqueous reaction medium in a reaction zone at a total acid normality of up to about 7 normal in the substantial absence of sulfate ion and in the presence of a dead load of sodium chlorate added to and subsequently removed from the reaction medium. Chloric acid for the process is produced electrolytically from an aqueous solution of the deadload sodium chlorate and make-up quantities of sodium chlorate. The chloric acid reduction to produce chlorine dioxide may be effected using methanol or electrolytically.

Chlorine dioxide is produced from sodium chlorate, sulphuric acid and methanol at the boiling point of the reaction medium under a subatmospheric pressure applied to a reaction zone. High purity of chlorine dioxide production is retained while the proportion of acid sodium sulphate in the product is decreased by effecting the reaction at high acidity in a physically-separate reaction zone from which the reaction products discharge into a mass of recycling sodium chlorate solution.

Production of chlorine dioxide

Chlorine dioxide is generated at high efficiency from feeds of chlorate cell liquor, sulphuric acid and methanol by a hybrid of reaction of sodium chlorate with sulphuric acid and methanol and reaction of sodium chlorate with sulphuric acid and sodium chloride. The reaction medium is maintained at its boiling point under a subatmospheric pressure while sodium sesquisulphate precipitates from the reaction medium.

Chlorine dioxide, particularly for water treatment but useful in other applications of chlorine dioxide, such as the bleaching of pulp, is produced in an enclosed reaction zone filled with chlorine dioxide-generating reaction medium under sufficient pressure to prevent chlorine dioxide from forming a continuous gaseous phase and the resulting aqueous solution of chlorine dioxide in spent reaction medium is discharged to a recipient aqueous medium, such as a flowing water body to be treated, without the formation of gaseous phase chlorine dioxide.

Small scale generation of chlorine dioxide for water treatment

Chlorine dioxide is formed at high efficiency from a solution of acid sodium chlorate at high sulphuric acid normality to which methanol is fed. The reaction medium is at its boiling point under a subatmospheric pressure. Total acid normality values in the range of about 7 to about 9 normal may be used while high efficiency of chlorine dioxide production is maintained.

High efficiency chlorine dioxide process

Chlorine dioxide is formed at high efficiency from a solution of acid sodium chlorate at high sulphuric acid normality in excess of 9 normal to which methanol is fed. The reaction medium is at its boiling point under a subatmospheric pressure. The incidence of white-outs is avoided by feeding chloride ions to the reaction medium, while the efficiency of chlorine dioxide production remains high.

Chlorine dioxide process

Chlorine dioxide for waste water treatment is formed by reaction of sodium chlorate, sodium chloride and sulphuric acid at high acidity while the reaction zone is subjected to subatmospheric pressure and spent reaction medium overflows from the reaction zone. The subatmospheric pressure preferably is applied using a water eductor to which the water to be treated is fed, so that direct contact between the produced gases and the water to be treated is effected.

Production of chlorine dioxide on a small scale

A chlorine dioxide generating process is described wherein chlorine formed with the chlorine dioxide is used to form acid reactant for the chlorine dioxide generating process by reaction with sulphur dioxide and water. The substantial evaporation of the water which would otherwise result from the exothermic nature of the reaction is prevented by controlling the temperature of the water during the reaction. In one embodiment, the temperature control is achieved by effecting the reaction in a cooled falling film absorber having integral cooling passages and to which liquid water is fed to form the falling film. In another embodiment, the reaction is effected in a packed tower with a substantial proportion of the product acid being recycled through an external heat exchanger and diluted with water.

Chlorine dioxide production using mixed hydrochloric and sulfuric acid

A mixture of hydrochloric acid and sulphuric acid for use as a feed to a chlorine dioxide generator to provide reactant chemicals therefor is formed by the reaction of chlorine, sulphur dioxide and water. The reaction is effected in the presence of excess chlorine to avoid the presence of dissolved sulphur dioxide in the acid mixture. The proportion of the excess of the chlorine also can be used to control the strength of the acid mixture which can be made without dissolved sulphur dioxide.

Production of mixed sulfuric and hydrochloric acid feed and chlorine

A highly efficient chlorine dioxide generating process which produces chlorine-free chlorine dioxide and neutral solid phase sodium sulphate from sodium chlorate, sulphuric acid and methanol is described. Solid phase sodium acid sulphate recovered from the high acidity reaction medium is metathesized using controlled quantities of water and controlled quantities of methanol to form the solid phase neutral sodium sulphate. Sulphuric acid recovered from the acid sulphate by the metathesis is recycled to the generator along with a part of the methanol used in the metathesis.

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Mississauga, Canada

Maurice C Fredette