Enhancing Pressurized Peroxide Bleaching of Kraft Pulps with Organophosphonate-Based Bleach Stabilizers, 1999 Pulping Conference Proceedings

Brian N. Brogdon, John M. Bell & Kevin M. Hale

Vinings Industries, Inc.

Recent process improvements in peroxide bleaching, such as pressurization and higher reaction temperatures have extended the versatility of peroxide for brightening kraft pulps. Management of the pulp’s metals profile has been shown to be a key factor for the successful implementation of pressurized peroxide bleaching. In this paper, we examine chelation and the addition of bleach stabilizers to a final PHT-stage as metals management strategies.

Initial laboratory studies indicated that the addition of organophosphonate-based stabilizers to a PHT-stage generally worked better at enhancing brightness (~1 point) than the addition of aminocarboxylate-based stabilizers or MgSO4. Similar PHT brightening responses were observed with the addition organophosphonate-based stabilizers to the PHT-stage versus a DTPA chelation stage. These results suggested that bleach stabilizers addition can be as effective as a chelation stage and can eliminate an extra processing stage in bleaching. Overall, the use of the various bleach stabilizers was not observed to negatively impact intrinsic fiber strength or pulp viscosity.

The results from one of the laboratory studies were applied to the successful start-up of a final PHT-stage at a North American mill. Tests were conducted with an aminocarboxylate- and an organophosphonate-based bleach stabilizer. Mill results demonstrated that the organophosphonate-based stabilizer, when compared against the aminocarboxylate formulation, was able to improve the final brightness by ~1 point if the process conditions were unchanged. Further tests indicated that the peroxide usage could be roughly reduced by one-third which resulted in a $3 to $4/ton decrease in PHT bleaching cost for a given target brightness. The outcome of the mill trial showed that organophosphonate-based stabilizers can be successfully used as a metals management strategy in PHT bleaching.