Mechanism of the Methanol Based C1O2 Generation Process, 1996 International Pulp Bleaching Conference Proceedings

The development of chlorine dioxide, chlorous acid, chlorine and chloride during the methanol based chlorine dioxide generation process has been determined. Accordingly three distinct phases, namely the initiation phase, the start-up phase and the steady-state phase have been identified. In the initiation phase, it was found that no chlorine dioxide is generated while chlorous acid, chloride and chlorine are gradually formed. Chlorous acid is produced from the reduction of chloric acid by methanol, and/or formaldehyde, and/or formic acid. The in-situ generated chlorous acid is further reduced to hypochlorous acid. Chloride is generated from chlorous acid in three possible reactions, and it is a catalyst in the reaction between chlorine and chlorous acid, which is responsible for the generation of chlorine dioxide in the methanol based ClO2 process. Due to an extremely low concentration of chloride in the initiation phase, this reaction is not taking place, as a result, no chlorine dioxide is generated. In the start-up phase, due to the accumulation of chloride in the initiation phase, the reaction between chlorine and chlorous acid becomes possible. As a result, chlorine dioxide is now generated while chloride is formed from the same reaction. Chlorate continues to be reduced to chlorous acid and hypochlorous acid. In the steady-state phase, the concentrations of both chloride and chlorous acid are constant. No chlorine is detected. Chlorine dioxide is the only overall reaction product. Chloride is essentially a “catalyst” in the chlorine dioxide generation cycle because it is consumed in the reduction of chlorate, but reformed in the ClO2 generation reaction between chlorine and chlorous acid.