The Effect of Sulfuric Acid, Persulfate and Acetic Anhydride on the Preparation of Chlorine Dioxide from Chlorite Solution

Abstract

The study was attempted to generate ClO2 from chlorite ion in a well stirred process aiming at a small scale production for the use of disinfection, sterilization and water purification etc. There were four reactants, H2SO4, Na2S2O8, (CH3CO) 2O and a mixture of H2SO4 and (CH3CO) 2O reacted individually with NaClO2 to produce ClO2. The main objective of the study was to achieve the maximum percentage production of ClO2 from chlorite solution. The analytical procedures were devised to determine chlorine dioxide, chlorite, chlorate and chloride ions in the composite reaction mixtures in order to determine the reaction order and propose possible chemical reactions for the formation and decomposition of ClO2. The reactions were carried out with various concentrations of NaClO2 (0.01, 0.05, 0.1 and 0.2N) and H2SO4 (0.02, 0.1, 0.2, 0.4 and 1.0N) at different time intervals. The production of ClO2 greatly depended on both the reactant concentrations and reaction time. The maximum percentage production of ClO2 was found to be 75% from the reaction between 0.01N NaClO2 and 1.0N H2SO4 in 240 minutes. Similarly, other reactions for the production of ClO2 from different reactants were illustrated as: a) about 60% ClO2 was produced in the reaction of 0.01N NaClO2 and 0.2N Na2S2O8 in 240 minutes, b) about 78% ClO2 was produced in the reaction of 0.01N NaClO2 and 0.1N (CH3CO)2O within two minutes and c) about 91% ClO2 was produced in the reaction of 0.01N NaClO2 with a mixture of 0.1N (CH3CO)2O and 0.02N H2SO4 concentrations within two minutes. Above results showed that 0.01N NaClO2 was the most suitable concentration for the production of ClO2 from chlorite solution. About 78% and 2% ClO2 were produced, respectively from (CH3CO)2O and H2SO4 reacted individually with NaClO2 within two minutes of reaction time and their sum was 80%, which was lower than that of the percentage production (91%) obtained in the reaction between NaClO2 and the reactant mixture [(CH3CO)2O and H2SO4]. The reaction between NaClO2 and the mixture [(CH3CO)2O and H2SO4] showed the better production efficiency of ClO2 than sum of their individual effects. In this reaction, either (CH3CO) 2O or H2SO4 was not acted as a catalyst because they reacted individually with NaClO2 to produce ClO2. Thus the synergistic effect of (CH3CO)2O and H2SO4 might be the cause of maximum production of ClO2. The study proposed reactions for ClO2 generation and decomposition based on the experimental results of the reaction between NaClO2 and H2SO4. It was observed that ClO2 is a very unstable compound, decomposes readily and forms various chlorine species in a series of reactions, and at the end of the reaction, the decomposition amount of ClO2 was almost equal to the formation amount of Cl−. Thus the proposed reactions for ClO2 generation and decomposition can be written as follows: The reaction order was determined using the reaction of NaClO2 and H2SO4 at 30 ± 10C. On the basis of the rate law, and finally a plot of dx/dt against (a-x) gave a straight line indicating the first-order reaction. The results showed that the experimental data did not fit to the equations of other order reactions. Hence, it was concluded that the decomposition reaction of ClO2- ion for the generation of ClO2 followed the first-order kinetics.