| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for ECF (elemental chlorine-free) bleaching of kraft pulp by which an increase in efficiency with an acid treatment can be exhibited to the maximum to obtain pulp of high brightness and the amount of a chlorine beaching chemical used can be reduced to suppress both the formation of organochlorine compounds as a by-product and the environmental pollution with bleaching waste liquors. SOLUTION: The method for ECF bleaching of the kraft pulp is characterized as follows. Unbleached pulp subjected to a digestion treatment is bleached with oxygen and multi-stage bleaching is then carried out. In the multi-stage bleaching process, an acid treatment stage is provided just after a treatment in chlorine dioxide stage of the first stage, and is carried out under bleaching conditions composed of 50-95°C reaction temperature, 60-180 min reaction time and pH 2.0-4.0 at the reaction end. The multi-stage bleaching stage is characterized in that the multi-stage bleaching treatment is preferably composed of the chlorine dioxide stage-acid treatment stage-alkali treatment stage or an alkali/oxygen stage-chlorine dioxide stage, the chlorine dioxide stage-acid treatment stage-alkali treatment stage or the alkali/oxygen stage-hydrogen peroxide stage-chlorine dioxide stage, the chlorine dioxide stage-acid treatment stage-alkali/peroxide stage or an alkali/oxygen/peroxide stage-chlorine dioxide stage. COPYRIGHT: (C)2005,JPO&NCIPI
|
