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Effects of metal catalysed peroxide decomposition on the bleaching of mechanical pulp

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Brown, DG (1993) Effects of metal catalysed peroxide decomposition on the bleaching of mechanical pulp. PhD thesis, University of Tasmania.

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Abstract

Hydrogen peroxide is widely used as an industrial bleaching agent, particularly for the
bleaching of mechanical pulps. Under the alkaline conditions required for effective
bleaching a number of transition metal ions, including iron, copper and manganese,
catalytically decompose peroxide resulting in a loss in the concentration of active
bleaching reagent, with a subsequent reduction in the bleaching efficiency. In this
study the effects of transition metal ions on the decomposition of hydrogen peroxide
have been studied, both in the presence and absence of pulp. The influence of various
additives, including sodium silicate and magnesium, on the rates of metal catalysed
peroxide decomposition have also been studied. The results of studies of the stability of alkaline hydrogen peroxide solutions in the
absence of pulp have demonstrated that the behaviour of transition metal ions towards
decomposition depends on the hydrolysis species of the metal present. Changes in the
rate of decomposition over the course of the reaction can be attributed to changes in the
catalytically active species present. The addition of a number of additives to peroxide
solutions containing added transition metal ions can also lead to changes in the
observed catalytic activity, either accelerating the rate of decomposition or stabilizing
the systems. In the presence of these additives a correlation was observed between the
catalytic activity of the transition metals and the formation of transition metal-additive
complexes, which could be monitored by UV-visible spectroscopy. This implies that a
direct interaction between the metal ions and additives is responsible for the observed
changes in the catalytic activity. It is proposed that the mechanism by which the
additives operate is by the formation mixed hydrolysis species with the transition metal
ions, with the resulting species having altered catalytic properties.
Studies of the effects of metal catalysed decomposition in the presence of pulp were conducted using a P. radiata TMP. The addition of the desired metal ions to prechelated
pulp enabled their catalytic activities to be determined individually. The
effects of sodium silicate and magnesium on the rates of metal catalysed decomposition
were also determined in the presence of pulp. Comparison of the behaviour of these
systems in the presence and absence of pulp reveals that the inclusion of pulp can have
a significant influence on the catalytic activities. These results demonstrate that it is not
possible to predict the peroxide decomposition behaviour during bleaching from
studies conducted in the absence of pulp.

Item Type: Thesis (PhD)
Keywords: Hydrogen peroxide, Wood-pulp, Papermaking
Copyright Holders: The Author
Copyright Information:

Copyright 1993 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1994. Includes bibliographical references (p. 219-230)

Date Deposited: 25 Nov 2014 00:42
Last Modified: 11 Mar 2016 05:55
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