Mikhail Balakshin, Chen-Loung Chen, Josef S. Gratzl, Adrianna G. Kirkman, Harald Jakob
Biobleaching of Pulp with Dioxygen in the Laccase-Mediator System. Part 1. Kinetics of Delignification
Summary
Kinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects
of variable factors on the delignification were studied. The delignification was conducted in acetate
buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could
be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order
rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage
of 10 U Coriolus laccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to
first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The
amounts of dioxygen consumed per removal of one C9-unit equivalent of residual lignin is rather high,
1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions
between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit
the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments
by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage
process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed
by alkaline extraction (E), (LMS-E)4, decreased kappa number of a pine kraft-AQ pulp from 21.8 to
less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 54, 07/2000
Pages: 390 - 396
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