Magnesium hydroxide-based peroxide bleaching of high-brightness mechanical pulps
Hietanen, Tomi (2013-11-20)
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Väitöskirja
Hietanen, Tomi
20.11.2013
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Tiivistelmä
A high final brightness is desired in most paper and board products. This requires
bleaching processes that are able to produce high-brightness pulps. Mechanical pulps are
widely bleached for high brightness using alkaline hydrogen peroxide with traditional
sodium hydroxide and sodium silicate as additives. With high doses however, peroxide
bleaching causes high organic loads in the mill effluent and anionic trash carry-over to
papermaking.
To alleviate the problems that arise from the use of sodium-based additives in peroxide
bleaching, interest in the use of alternative magnesium-based chemicals has increased. In
this study, a new, technical high-purity magnesium hydroxide-based bleaching additive
was evaluated on laboratory-scale, pilot-scale and mill-scale experiments and trials for its
ability to produce a high brightness in peroxide bleaching without the known problems of
sodium-based chemicals.
The key findings of this study include: a high brightening potential of peroxide bleaching
using the Mg(OH)2-based additive, significant reductions (40-70%) in all categories of
environmental load, and cationic demand lowered by 60-70% in bleached pulp with no
loss in strength properties or in sheet bulk. When used in TMP refiner bleaching, the
Mg(OH)2-based additive resulted in savings in specific energy consumption and provided a
good bleaching response.
bleaching processes that are able to produce high-brightness pulps. Mechanical pulps are
widely bleached for high brightness using alkaline hydrogen peroxide with traditional
sodium hydroxide and sodium silicate as additives. With high doses however, peroxide
bleaching causes high organic loads in the mill effluent and anionic trash carry-over to
papermaking.
To alleviate the problems that arise from the use of sodium-based additives in peroxide
bleaching, interest in the use of alternative magnesium-based chemicals has increased. In
this study, a new, technical high-purity magnesium hydroxide-based bleaching additive
was evaluated on laboratory-scale, pilot-scale and mill-scale experiments and trials for its
ability to produce a high brightness in peroxide bleaching without the known problems of
sodium-based chemicals.
The key findings of this study include: a high brightening potential of peroxide bleaching
using the Mg(OH)2-based additive, significant reductions (40-70%) in all categories of
environmental load, and cationic demand lowered by 60-70% in bleached pulp with no
loss in strength properties or in sheet bulk. When used in TMP refiner bleaching, the
Mg(OH)2-based additive resulted in savings in specific energy consumption and provided a
good bleaching response.
Kokoelmat
- Väitöskirjat [1108]