| 摘要 |
When gaseous oxygen and alkali are used to delignify and bleach a chemical cellulosic half-stuff, it is not possible to remove more than about half of the quantity of lignin remaining in the cellulosic half-stuff after digestion, since there exists the danger of an intense and uncontrollable decomposition of the carbohydrates in the cellulosic half-stuff. According to the invention, it is now possible to remove three-quarters of the quantity of the residual lignin while retaining good half-stuff properties; the present invention is concerned with a process for delignifying a chemical cellulosic half-stuff in which the half-stuff is brought into contact with a gas phase containing NO2 in an activation stage, and gaseous oxygen is fed to the activation stage so that the nitrogen oxide formed as an intermediate product is used to activate the half-stuff and the activation stage is performed under severe conditions, characterised in that the half-stuff is then subjected in a half-stuff/water mixture to an oxygen gas/alkali treatment process, the partial pressure of the gaseous oxygen during the oxygen gas/alkali treatment process being kept to 0.005 to 0.18 MPa, and the partial pressure of the gaseous oxygen does not fall below the lower partial pressure limit in any portion of the treatment process.
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