Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Gas – vapor or mist contact
Patent
1995-10-31
1997-03-18
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Gas, vapor or mist contact
162 78, 162 80, D21C 9147, D21C 916
Patent
active
056118899
ABSTRACT:
A process for bleaching high-yield (mechanical or chemi-mechanical) pulps to high brightnesses and low yellownesses (b*) in a single treatment employs di-oxygen gas (O.sub.2), alkaline agent and a borohydride. The combined treatment gives brightnesses comparable with those achieved with stabilized alkaline hydrogen peroxide. By comparison the reaction of di-oxygen and alkali alone darkens high-yield pulps; and treatment with alkaline borohydride in the absence of added di-oxygen bleaches to give only about half the brightness gained if di-oxygen is added. The bleaching may possibly occur through the conversion of di-oxygen molecules (O.sub.2) to hydroperoxide ions (HOO-) utilizing ionized phenolic groups or hydroquinones in the lignin. The hydroperoxide ions are thus generated in situ in the lignin and can destroy colored lignin chromophores. Without the addition of borohydride the lignin phenolic groups would be irreversibly oxidized. The primary role of the borohydride is to regenerate the phenolic groups and maintain a di-oxygen hydroperoxide (O.sub.2)(HOO-) cycle. In a secondary role, the borohydride also contributes to the bleaching by reducing radicals, organic peroxides and carbonyl compounds in the pulps.
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Giampaolo David
Leary Gordon
Alvo Steve
Pulp and Paper Research Institute of Canada
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