Kinetic study of the mechanism and side reactions in the hydrogen peroxide based production of chlorine dioxide

The purpose of this work was to examine the mechanism governing chlorine dioxide formation from commercial systems that use sulfuric acid, sodium chlorate and hydrogen peroxide to produce chlorine dioxide. The primary consumer of chlorine dioxide is the pulp and paper industry where it is used to bleach wood pulp, but chlorine dioxide is also gaining interest in many disciplines of water treatment. Advantages of peroxide-based production of chlorine dioxide include: reduction in the amount of salt cake produced, elimination of an organic reducing agent, lack of production of significant amounts of chlorine as a by-product and use in existing facilities with increased capacity.; An important feature of commercial systems that employ the hydrogen peroxide chemistry is the presence of chloride ion in the generator. We found that chloride ion significantly altered the mechanism and rate of chlorine dioxide formation. The rate of chlorine dioxide formation from hydrogen peroxide and chloride ion far exceeded that due solely to hydrogen peroxide, suggesting that a chloride-chlorate mechanism dictated chlorine dioxide formation. We proposed a chloride-chlorate mechanism and discovered that the addition of a sufficient concentration of hydrogen peroxide produced a maximum in the rate of chlorine dioxide formation. This maximum was explained in terms of the proposed mechanism.; We examined the system of sulfuric acid, sodium chlorate, hydrogen peroxide and chloride ion in a continuous stirred tank reactor. Our analysis indicated that hydrogen peroxide was inefficiently consumed in this system. We proposed two side reactions to account for this inefficiency, but further experimental investigation revealed that these steps were not the source of the inefficiency. We were unable to positively identify the source of inefficient hydrogen peroxide consumption.; We also examined the reaction mechanism governing chlorine dioxide formation from hydrogen peroxide in the absence of chloride. Knowledge of this mechanism is important in systems with high hydrogen peroxide concentration and smaller scale flow through systems in which chloride ion would not accumulate to a high level. We proposed a mechanism for chlorine dioxide formation which was consistent with a previously generated empirical model.