Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1026—Other features in bleaching processes

Definitions

• an unbleached pulp is first treated with chlorine to chlorinate lignin contained in the pulp fibers, and to impart a solubility in water thereto, then treated with an aqueous alkali solution to dissolve and extract the chlorinated lignin in the aqueous alkali solution, and to remove lignin from the pulp fibers, and finally treated with a hydrochlorite or chlorine dioxide to decompose and remove the residual lignin in the pulp fibers and to obtain a bleached pulp having a high brightness.
• the acid treatment under the conditions as disclosed causes only a decrease in apparent Kappa number of the pulp, but does not contribute to delignifying the pulp. Therefore, the acid treatment does not enhance the bleaching effect on the pulp and the decrease in consumption of the bleaching chemical for the bleaching procedure is unsatisfactory.
• Japanese Unexamined Patent Publication No. 6-280,177 discloses a process for bleaching a pulp by acid treating an unbleached pulp prepared by cooking wood chips in an aqueous inorganic acid solution at a pH value of 1.0 to 1.6 at a temperature of 80°C to a boiling temperature of the aqueous acid solution at a pulp consisting of 5 to 20% by weight for 1 to 3 hours, and the acid-treated pulp is subjected to an alkali extraction treatment for lignin in the pulp.
• the inventors of the present invention further researched the acid treatment of the wood pulp under pressure in the presence of no catalyst.
• the acid treatment of the wood pulp is carried out in an oxygen and/or nitrogen-containing gas under pressure, the delignification of the wood pulp is very significantly promoted, and the resultant delignified pulp can be easily bleached with a bleaching chemical by a single or multi-step bleaching procedure, in comparison with the acid-treated pulp under no pressure, and thus the consumption of the bleaching agent could be reduced.
• the cooking additive is added in an amount of 0.001 to 1.0% by weight based on the bone dry weight of the wood chips to the cooking liquor.
• waste water discharged from the acid treating step may be recovered.
• the waste water is optionally fed, together with a waste water recovered from a cooking step, into a boiler for recovered waste, to burn organic substances dissolved or suspended in the waste water and to generate heat energy.
• Example 2 The same unbleached hardwood kraft pulp as in Example 1 was suspended in a bone dry weight of 90.0g in ion-exchanged water, and added with sodium hydroxide in an amount of 1.5% based on the bone dry weight of the pulp.
• the aqueous unbleached pulp slurry was diluted with ion-exchanged water to adjust the pulp consistency in the slurry to 10% by weight.
• the resultant lignified pulp was washed with ion-exchanged water, and dewatered.
• An oxygen lignified pulp having a Hunter brightness of 51.1%, a Kappa number of 10.2, and a pulp viscosity of 18.8 mPa ⁇ s was obtained in a bone dry weight of 88.8g.
• the pulp yield in the PO bleaching procedure was 99.4% and the total pulp yield in the acid-treatment and bleaching procedures was 98.4%.
• the resultant bleached pulp was collected in a bone dry weight of 68.7g with a pulp yield of 98.1% and had a Hunter brightness of 85.3%.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

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Cited By (3)

Citations (3)

• 1998
  • 1998-03-03 CA CA 2230961 patent/CA2230961A1/fr not_active Abandoned
  • 1998-03-03 EP EP98660014A patent/EP0863251A1/fr not_active Withdrawn

Patent Citations (3)

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