Some Factors Affecting Chloroform Generation During Chlorine Dioxide Bleaching of Pulp, 2000 Environmental Conference Proceedings

- J. Louch, R. Messmer, G. Wilson -- A study employing laboratory-scale bleaching was performed to characterize the relationship between specific bleach plant parameters and chloroform generation from chlorine dioxide bleaching, i.e., elemental chlorine free (ECF) bleaching. The experiments carried out conformed to a four-factor/two-level factorial study design, and the four bleach plant parameters studied were D0-stage final pH, D0-stage kappa factor, chlorine dioxide (ClO2) source, and pulp source. Results from the factorial study indicated that D0-stage final pH and ClO2 source both had significant effects on chloroform generation in the laboratory-scale bleaches, and that D0-stage final pH and kappa factor interacted. In this study, chloroform generation in laboratory D0E1 stages increased with D0-stage final pH over the range from pH 1.9 to 3.5 and, in seven of eight cases, ClO2 containing 1.7% Cl2 as a byproduct gave less chloroform than was generated using ClO2 containing 13% Cl2. The interaction between D0-stage final pH and kappa factor manifested as more chloroform being produced at kappa factor 0.30 than at kappa factor 0.15 when D0-stage final pH was 1.9, but less chloroform at kappa factor 0.30 than at kappa factor 0.15 when D0-stage final pH was 3.5. The two experimental pulps did not give significantly different amounts of chloroform in these laboratory-scale bleaching experiments and, overall, D0-stage final pH was ranked as the factor having the greatest numerical impact on chloroform generation, followed by kappa factor, then ClO2 type. Additional experiments confirmed that D-stage carryover can increase E-stage chloroform, and the data suggested that approximately 10% carryover of laboratory D0-stage filtrates would have resulted in a 10% to 40% increase in the associated E1-stage chloroform levels. Finally, the median contribution from D1E2 stages to chloroform generation in laboratory D0E1D1E2 stages was 43%.