The objective of this study was to evaluate different variations of
the combination of a hot chlorine dioxide (Dhot) stage and an acidic
molybdate catalyzed hydrogen peroxide stage (PMo), and to compare
to other state-of-the-art options for a first bleaching stage after
oxygen delignification and prior to an alkaline extraction stage.
Laboratory bleaching trials were conducted with oxygen delignified
eucalyptus kaft pulp samples provided by Brazilian pulp mills,
with kappa numbers ranging between 10.0 and 12.9, and initial
brightness values ranging between 50.0% and 56.5% ISO. Surprisingly
and in contrast to previous scientific and patent literature,
the Dhot/PMo process variant, i.e. a short hot chlorine dioxide
stage followed without intermediate washing by an extended acidic
molybdate catalyzed hydrogen peroxide stage turned out to be most
effective with regard to kappa number reduction and brightness gain
while causing only a moderate viscosity loss which is even smaller than
observed in a single Dhot stage. It also allows a significant reduction
of the chlorine dioxide charge in its Dhot part. Full bleaching
sequences were run including the four-stage bleaching sequence
Dhot/PMo-EP-D1-P and the three-stage bleaching sequence Dhot/PMo-EP-D/P,
which were compared to the conventional state-of-the-art four-stage
bleaching sequence Dhot-EP-D1-P with respect to brightness gain,
brightness stability, and chemical consumption. A recently developed
economical recovery and recycle process for the molybdate catalyst is
briefly introduced as well.

Authors’ references:
1. Evonik Degussa Brasil Ltda., Alameda Campinas, 579, 3rd to 12th floor, 01404-000 São Paulo – SP, Brazil - E-mail: cesar.leporini@evonik.com
2. Evonik Degussa GmbH, Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang, Germany – E-mail: thomas.dietz@evonik.com
Corresponding author: Thomas Dietz – E-mail: thomas.dietz@evonik.com

O PAPEL vol. 72, num. 7, pp. 42 - 46 JUL 2011