Abstract: Chlorine with a low bromine content is produced by electrolyzing brine to produce gaseous chlorine, alkali metal hydroxide and hydrogen, separating the gaseous chlorine from the electrolyte (anolyte in the case of the membrane process), directing electrolyte (anolyte in the case of the membrane process) to a primary dechlorination step using hydrochloric acid to remove gaseous chlorine therefrom, optionally directing depleted electrolyte (anolyte in the case of the membrane process) from the primary dechlorination step to a secondary dechlorination step using a reducing agent for chlorine and oxychlorine species, and recycling dechlorinated depleted electrolyte (anolyte in the case of the membrane process) to salt dissolvers to prepare brine for electrolysis. At least part of the gaseous chlorine generated in the primary dechlorination step is not combined with gaseous chlorine generated in the electrolysis step.

Abstract: Chlorine with a low bromine content is produced by electrolyzing brine to produce gaseous chlorine, alkali metal hydroxide and hydrogen, separating the gaseous chlorine from the electrolyte (anolyte in the case of the membrane process), directing electrolyte (anolyte in the case of the membrane process) to a primary dechlorination step using hydrochloric acid to remove gaseous chlorine therefrom, optionally directing depleted electrolyte (anolyte in the case of the membrane process) from the primary dechlorination step to a secondary dechlorination step using a reducing agent for chlorine and oxychlorine species, and recycling dechlorinated depleted electrolyte (anolyte in the case of the membrane process) to salt dissolvers to prepare brine for electrolysis. At least part of the gaseous chlorine generated in the primary dechlorination step is not combined with gaseous chlorine generated in the electrolysis step.

Abstract: Chlorine with a low bromine content is produced by electrolyzing brine to produce gaseous chlorine, alkali metal hydroxide and hydrogen, separating the gaseous chlorine from the electrolyte (anolyte in the case of the membrane process), directing electrolyte to a primary dechlorination step using hydrochloric acid to remove gaseous chlorine therefrom, optionally directing depleted electrolyte (anolyte in the case of the membrane process) from the primary dechlorination step to a secondary dechlorination step using a reducing agent for chlorine and oxychlorine species, and recycling dechlorinated depleted electrolyte (anolyte in the case of the membrane process) to salt dissolvers to prepare brine for electrolysis. At least part of the gaseous chlorine generated in the primary dechlorination step is not combined with gaseous chlorine generated in the electrolysis step.

Abstract: Chlorine dioxide is produced at high conversion rates from aqueous sodium chlorite solution by electrochemical oxidation in an undivided electrochemical cell. The cell utilizes an anode of high surface area through which the aqueous sodium chlorite solution flows into an interelectrode gap between the anode and a cathode. Water or acidified water is fed into the interelectrode gap to function as catholyte and also to dilute the electrolyzed sodium chlorite solution to provide an aqueous solution of chlorine dioxide exiting from the electrochemical cell.

Abstract: A greater yield of chlorine dioxide from a chlorine dioxide generating process is obtained by providing acidic or acidity-generating components in the product chlorine dioxide solution to provide a chlorine dioxide solution having a pH below about 5.5.

Abstract: Chlorine dioxide is produced at high conversion rates from aqueous sodium chlorite solution by electrochemical oxidation in an undivided electrochemical cell. The cell utilizes an anode of high surface area through which the aqueous sodium chlorite solution flows into an interelectrode gap between the anode and a cathode. Water or acidified water is fed into the interelectrode gap to function as catholyte and also to dilute the electrolyzed sodium chlorite solution to provide an aqueous solution of chlorine dioxide exiting from the electrochemical cell.

Abstract: A greater yield of chlorine dioxide from a chlorine dioxide generating process is obtained by providing acidic or acidity-generating components in the product chlorine dioxide solution to provide a chlorine dioxide solution having a pH below about 5.5.

Abstract: A process for converting in a single pass an aqueous alkaline pH, alkali metal chlorite solution into an aqueous chlorine dioxide-containing solution that involves the combination of (1) using an electrochemical acidification cell to lower the pH value of the aqueous alkali metal chlorite feed before it enters the anode compartment of an electrochemical oxidation cell where the chlorite is converted to chlorine dioxide with (2) using an anolyte flow pattern where the anolyte passes through a porous, high surface area electrode. This process results in a substantially improved conversion efficiency per pass.

Abstract: Chlorine dioxide is generated by electrochemical oxidation of sodium chlorite in an anode compartment of a cation-exchange membrane-divided cell in the presence of significant quantities of sodium chlorate and is recovered in a suitable recipient medium by passing the chlorine dioxide through a hydrophobic microporous membrane. Water balance in a continuous operation is maintained by removing water from the anolyte by transporting the same partly across the hydrophobic microporous membrane in vapor form and partly across the cation-exchange membrane.

Abstract: An in-situ procedure is described for measuring chlorate ion concentration in aqueous media containing the same by employing electrodes, particularly microelectrodes which generate a sigmoidal-type response at high chlorate ion concentration, and which exhibit catalytic properties toward chlorate ion electroreduction or electrooxidation.

Abstract: Chlorine dioxide is generated by electrochemical oxidation of sodium chlorite in an anode compartment of a cation-exchange membrane-divided cell and is recovered in a suitable recipient medium by passing the chlorine dioxide through a hydrophobic microporous membrane. Water balance in a continuous operation is maintained by removing water from the anolyte by transporting the same partly across the hydrophobic microporous membrane in vapor form and partly across the cation-exchange membrane.

Abstract: Chlorine dioxide is produced by reaction of chlorate ions, usually provided by sodium chlorate, with a persulfate in an aqueous acid reaction medium containing sulfuric acid. By-product sodium sulfate, sulfuric acid feedstock or mixture may be electrolyzed to form the persulfate for the reaction.

Abstract: Chlorine dioxide is produced by reaction of sodium chlorate, a reducing agent, preferably methanol or hydrogen peroxide, and sulfuric acid at the boiling point of the reaction medium under a subatmospheric pressure. Present in the reaction medium is a component which suppresses the solubility of by-product sodium sulfate and thereby increases the concentration of free hydrogen ions in the reaction medium available for reaction to form chlorine dioxide. The solubility-depressing component generally is an inert alkali metal salt, preferably an inert sodium salt, such as perchlorate or nitrate. By increasing the concentration of hydrogen ions available for reaction, it is possible to achieve an improvement in the rate of production of chlorine dioxide.

Abstract: A salt solution, particularly aqueous sodium chlorate, is acidified electrolytically at a higher current efficiency than has previously been the case by employing a plurality of multiple compartment cells, in which the effluent from intermediate compartments is passed through more anodic compartments.

Abstract: 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.

Abstract: The voltage requirements of a membrane-divided cell are decreased by operating the cell with a catholyte temperature significantly in excess of the anolyte temperature, generally at least 10.degree. C. greater and preferably at least 20.degree. C. greater. The invention is particularly useful in an electrochemical acidification process whereby aqueous sodium chlorate and sodium sesquisulfate solution is acidified for use in a chlorine dioxide generating process and aqueous sodium hydroxide is produced as a by-product.

Abstract: The formation of sodium sulfate by-product in sulfuric acid-based chlorine dioxide generating processes is decreased and preferably eliminated entirely, by effecting electrochemical treatment of sodium ion-containing feed materials for the generator to remove sodium ions and to add hydrogen ions. Sodium hydroxide may be produced as a by-product. The process is generally applicable to the electrochemical treatment of alkali metal chlorates, alkali metal sulfates and mixtures thereof to produce acidified solutions useful in providing chlorate ion-containing feeds to such chlorine dioxide generating processes or for other purposes.

Abstract: 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.

Abstract: The formation of sodium sulfate by-product in sulfuric acid-based chlorine dioxide generating processes is decreased and preferably eliminated entirely, by effecting electrochemical treatment of sodium ion-containing feed materials for the generator to remove sodium ions and add hydrogen ions. Sodium hydroxide is produced as a by-product. The process is generally applicable to the electrochemical treatment of alkali metal chlorates, alkali metal sulfates and mixtures thereof to produce acidified solutions useful in providing chlorate ion-containing feeds to such chlorine dioxide generating processes.

Abstract: Chloric acid is produced in an electrolytic-electrodialytic process in which chlorate ions from a sodium chlorate solution are transferred through an anion-exchange membrane to combine with electrolytically-produced hydrogen ions in a compartment of a cell, from which the resulting chloric acid is recovered. The sodium ions are transferred through a cation-exchange membrane to combine with electrolytically-produced hydroxyl ions in another compartment of the cell, from which the resulting sodium hydroxide is recovered.