GENERALIZED STEADY-STATE STOICHIOMETRIC MODELS FOR CHLORINE DIOXIDE BRIGHTEN-ING STAGES FOR SOFTWOOD KRAFT PULPS, 2013 PEERS Conference

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A generalized, steady-state model is proposed for predicting brightness and/or bleach consumption during chlorine diox-ide brightening (D₁ and D₂) for softwood pulps treated with chlorine dioxide delignification sequences. The model is adapted from the D1 hardwood model of McDonough and co-workers, which related chlorine dioxide consumption to brightness gains with three tunable parameters. Literature data from various Elemental Chlorine-Free (ECF) bleaching studies were analyzed to find generalized relationships for the models’ parameters. Data analysis revealed that the ulti-mate brightness limits for both D₁ and D₂ models, at excessively high bleach charges, was ~92% ISO. Another parame-ter for the D₁ model was found to be a linear function of extracted kappa number, whereas for the D₂ model, the parame-ter was a linear function of post-D₁ brightness. The third equation parameter for the D₁ and D₂ models was found to be a function of the other two parameters and the entering brightness value. The generalized brightening models predict D1 brightness to ±1% ISO units and D₂ brightness to ±0.3% ISO units for a given amount of chlorine dioxide consumed. These relatively simple brightening models, which have a minimum number of equation parameters, can used in con-junction with other bleaching delignification models to simulate chemical consumption for a given ECF sequence.