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
  • D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
  • D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
  • D21C9/144—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 and other bleaching agents in a multistage process

Definitions

• My invention relates to improvements in the multistage bleaching of sulfite cellulose pulps and more particularly to a bleaching operation employing a combination of chlorine dioxide, particularly in the form of a chlorite, and chlorine in the first or preliminary bleaching stage.
• sulfite pulp has the advantage over sulfate pulp in that it is more readily bleached to a high whiteness and is thus more suitable for many grades of paper and other cellulose products, the high whiteness is frequently obtained at the expense of a considerable loss of strength. For this reason sulfate pulp is sometimes blended with sulfite pulp in spite of the sacrifice in color in order to obtain adequate strength.
• the minimum operation ordinarily consists of three stages, the first of which is a chlorination stage in which the pulp is treated with chlorine water for a period of about one hour at an acid pH.
• the lignin is largely chlorinated due to the presence in the acid solution of most of the chlorine as dissolved elemental chlorine. Oxidation is avoided by the acidity of the solution, the pH normally being about 1.8 to 2.0, which restricts the formation of hypochlorous acid, the oxidizing agent in the system.
• the chlorination reaction is relatively rapid compared to the oxidation reaction, limiting the time of contact also assists in avoiding oxidation.
• the pulp consistency is about 1.5 to 3 per cent and the preliminary bleach is carried out at the temperature of the available water.
• the chlorinated pulp is extracted with caustic, for example with 2 per cent caustic, at 120 to 140 F. using a 10 per cent pulp consistency.
• the bleach is completed by treatment with a hypochlorite under alkaline conditions.
• the resulting washed pulp has a brightness of about 80 to 82.
• a sulfite cellulose pulp in aqueous medium is partially bleached in a preliminary stage with sufiicient chlorine dioxide and chlorine to supply about 50 to 60 per cent of the chlorine requirement of the pulp as determined by the permanganate number and then bleached in a subsequent stage with an aqueous solution of a hypochlorite.
• the amount of the chlorine requirement of the pulp supplied to the preliminary partial bleaching stage by the chlorine dioxide is about 50 to per cent on an equivalent available chlorine basis.
• the pulp in aqueous medium is partially bleached in the preliminary stage with a chlorite and chlorine at a pH of about 2.5 to 2.7 at approximately room temperature.
• Example I Instead of the 30 pounds of chlorine conventionally supplied to partially bleach this pulp in the preliminary chlorination stage, 10 pounds of sodium chlorite together with 15 pounds of chlorine, 3 of which were necessary to activate the chlorite, were used. After the treatment had continued for one-half hour the pulp was filtered and washed. The caustic extraction was omitted and the pulp at a consistency of 12 per cent was treated with 28 pounds of available chlorine as calcium hypochlorite at a temperature of F. for two hours. test sheets showed a GE brightness of 80.7. The strength After washing,
• Example II The same pulp at a consistency of 2.5 per cent was treated with 20 pounds of available chlorine as sodium chlorite and pounds of chlorine per ton, 4 of which were utilized to activate the chlorite. After treatment in the preliminary chlorination stage for one-half hour the pulp was filtered, washed and reslurried to a consistency of 10 per cent with pounds of caustic per ton. The caustic extraction was continued at a temperature of 140 F. for one hour. After washing the pulp and reslurrying to a consistency of 12 per cent, it was treated with 9 pounds of available chlorine as calcium hypochlorite at a temperature of 95 F. for two hours. The finished pulp gave a test sheet having a brightness of 83.9.
• the strength retention was 92.8 per cent based on per cent Mullen values of 184 for the unbleached stock and 171 for the final pulp. Based on per cent tear values the strength retention was 111.5 per cent.
• the chlorine requirement in the first stage was reduced by 70 per cent of that when no chlorite was used and the total available chlorine requirement was reduced by per cent.
• Example 111 to per cent of the chlorine requirement of the pulp as determined by the permanganate number is supplied by chlorine followed by a later stage of bleaching with an aqueous solution of hypochlorite, the improvement which comprises partially bleaching the pulp in the preliminary stage in aqueous medium and under acid conditions with chlorine dioxide and chlorine, the amount of the chlorine requirement supplied to the preliminary partial bleaching stage by the chlorine dioxide being about 50 to per cent on an equivalent available chlorine basis.
• Sen Gupta Progressive Delignification of Jute Fibre with Chlorine Dioxide. J. Text. Inst. (Trans), September 1951, pgs. T375-384, especially first page.

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

Priority Applications (3)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23066179

Family Applications (1)

Country Status (3)

Cited By (6)

Citations (5)

• 0
  • BE BE518419D patent/BE518419A/xx unknown
• 1952
  • 1952-03-26 US US278747A patent/US2741536A/en not_active Expired - Lifetime
• 1953
  • 1953-02-24 FR FR1071422D patent/FR1071422A/fr not_active Expired

Patent Citations (5)

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