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Novel methods in peroxide bleaching

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Finnegan, Daniel James (1998) Novel methods in peroxide bleaching. Research Master thesis, University of Tasmania.

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Abstract

Hydrogen peroxide has been used by manufacturers of high yield mechanical pulps
as the preferred bleaching chemical. For example, Australian Newsprint
Mills(ANM) Ltd operates a hydrogen peroxide refiner bleaching Pine TMP plant at
its Albury mill and a peroxide tower bleaching plant at the Boyer mill processing
Eucalypt CCS.
Hydrogen peroxide bleaching requires alkaline conditions to form the active
bleaching species 001-1 - . However, under these conditions hydrogen peroxide is
very susceptible to transition metal ion catalysed decomposition. The metals
manganese, iron, and copper promote the greatest rate of peroxide decomposition.
DTPA is added to chelate the transition metal ions in the process and prevent
hydrogen peroxide decomposition. DTPA is a strong complexing agent and there are
some concerns about its environmental impact. Alternatives to DTPA have been
investigated. Recently a patent was published using Zeolite as an alternative
chemical to DTPA.
In this project the affect of zeolite and sodium citrate on peroxide decomposition and
bleaching of Pine TMP and Eucalypt CCS pulp has been investigated. Manganese, a
known decomposition catalyst, has been used to produce conditions which induce
peroxide decomposition. Various factors including pH, zeolite type, zeolite concentration and sodium citrate concentrations were all found to affect the rate of
peroxide decomposition and bleaching response.
Zeolite-A was found to reduce decomposition more than the other two zeolites, types
X and Y. Zeolite-A has a lower Si/A1 ratio which allows for greater cation
exchange. The combined zeolite and citrate system had the greatest stabilising effect
on decomposition of peroxide solutions in the presence of manganese under alkaline
conditions.
Zeolite-A also had a better bleaching response than the other zeolites. Combined
zeolite-A and citrate systems achieved brightness results slightly less than DTPA
though the residual peroxide concentrations were significantly lower for peroxide
bleaching of Pine TMP. The order of chemical addition is important. If the alkali is
added prior to zeolite, and manganese is oxidised from Mn2+ state to higher states
forming Mn-O-Mn type complexes, zeolite was found to be ineffective.
Consequently zeolite-A had no effect on manganese induce peroxide decomposition
leading to a poor peroxide bleaching response with Eucalypt CCS pulps.
Zeolite is believed to be acting as a chelating agent rather than as a catalyst for
hydrogen peroxide oxidation reactions (bleaching). Zeolite is able to cation
exchange Mn2+ ions but not Mn-O-Mn complexes. If Mn-O-Mn complexes are
allowed to form, decomposition of peroxide occurs. Addition of citrate helps
transfer Mn ions into the zeolite structure rather than providing an overall increase in
chelating ability. Addition of zeolite improves optical properties of handsheets by increasing opacity
and light scattering co-efficient which is beneficial to newsprint grades. No
significant losses in strength of handsheets occurred with the addition of zeolite.

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

Copyright 1998 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 (M.Sc.)--University of Tasmania, 1998. Includes bibliographical references

Date Deposited: 09 Dec 2014 00:03
Last Modified: 16 Aug 2016 01:31
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