Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Regulatory
Patent
1994-04-12
1995-10-10
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Regulatory
162 49, 162 65, 162 81, D21C 316, D21C 9147
Patent
active
054567998
ABSTRACT:
The method solves the problem of delignifying technical cellulose pulp in a selective manner which will result in very low residual contents of lignin in the pulp and a correspondingly high quantity of lignin dissolved in spent liquors, which are recovered in the chemical recovery system of the pulp mill. The method comprises activating liquid-containing lignocellulosic material in the presence of nitrate with a gas that contains nitrogen dioxide, followed by the alkaline delignification of the lignocellulosic material, and measuring the acidity of the liquid accompanying the material on at least one occasion during the activation. The method is characterized in that the acidity of the liquid is measured subsequent to bringing the time derivative of the nitrate concentration of the liquid, expressed as millimols per liter of liquid per minute, to a level beneath +0.2, and by using the measured acidity value to establish the optimum amount of mineral acid for continuation and termination of the activation, and by charging the whole of this quantity or a part of this quantity of mineral acid to the lignocellulosic material.
REFERENCES:
patent: 3888726 (1975-06-01), Hultman
patent: 4725335 (1988-02-01), Samuelson
patent: 4897156 (1990-01-01), Samuelson
Alvo Steve
Mo och Domsjo Aktiebolag
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