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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes

Definitions

• This invention relates to the delignification and bleaching of chemical and semichemical cellulose pulps by the action of oxygen in an alkaline medium.
• the bleaching of chemical cellulose pulps for the production of paper or of dissolving pulps for chemical uses generally requires several successive treatments to reach the desired amount of residual lignin and the required brightness.
• Bleaching agents commonly used for the treatment of cellulose pulps include chlorine, caustic soda, calcium and sodium hypochlorites, chlorine dioxide, sodium dioxide, hydrogen peroxide; the first are almost exclusively used for delingnification.
• a method has been dis covered which makes it possible, in a multistage bleaching operation, to substitute one operation for the first two operations of chlorination and alkaline extraction, and possibly for a subsequent hypochlorite treatment, the delignification and increase in brightness being usually greater than by known methods.
• the method of the invention has the greater advantage of well preserving the physical and mechanical characteristics of cellulose pulps, and even of improving them in some cases, while giving a very complete delignification and significant increase in brightness.
• This method for the delignification and bleaching of chemical and semichemical cellulose pulps under the action of, oxygen in an alkaline medium is characterized in that the treatment of the pulps is effected in the presence of a catalyst selected from the group consisting of barium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, alkali metal borates and titanium dioxide, used at a concentration from 0.5 to about 3% by weight of the pulp.
• a catalyst selected from the group consisting of barium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, alkali metal borates and titanium dioxide, used at a concentration from 0.5 to about 3% by weight of the pulp.
• Magnesium carbonate is the preferred catalyst according to the invention. When used in amounts of about 1% by weight of the pulp, it gives the best results.
• the unbleached pulp is treated, in an electrically heated, rotary autoclave, with a solution of caustic soda in the presence of the catalyst, at elevated temperatures, preferably between C. and 130 C., and particularly between 90 C. and C.
• Oxygen is introduced into the autoclave so as to get the desired pressure, usually in the range 510 bars.
• the cellulose pulps treated usually have a concentration ranging from 6% to 10%, and 8% to 12% NaOH is preferably used based on the pulp, according to the quality and degree of lignification of the latter.
• the concentrations given are concentrations by weight.
• the time of reaction at top temperature ranges from half an hour to a few hours, preferably between one and three hours.
• Catalyst MgCO (1% based on the pulp);
• Time of treatment 2 hrs. at 100 C.
• the various catalysts used in these trials are barium and calcium carbonates, titanium dioxide and sodium tetraborate.
• Catalyst MgCO (1% based on the pulp);
• Time of treatment 2 hrs. at 100 C.
• % beech Concentration of the pulp: 6.6%; Concentration of NaOH based on the pulp: 10%; Operating temperature: 100 C.; Oxygen pressure at 100 C.: 6.8 bars; Catalyst: 1% MgCO based on the pulp; Time of treatment: 2 hrs. at 100 C.
• Pulp concentration 6.6%; Concentration of NaOH based on the pulp: 11.3%; Oxygen pressure at 100 C.: 4.5 bars; 1% catalyst by weight based on the pulp; Time of treatment: 2 hrs. at 100 C.
• the examples illustrating the invention show the advantages of the use of a catalyst in the bleaching of pulps with oxygen in an alkaline medium, which makes it possible to obtain a very complete delignification and a significant increase in brightness, while preserving the physical characteristics of the treated pulps.
• the commercial application of the method can therefore be contemplated, so as to substitute an oxygen-caustic treatment for the chlorination and alkaline extraction phases at least.
• a method for the delignification and bleaching of chemical and semichemical cellulose pulps under the action of oxygen in an alkaline medium wherein the delignification and bleaching of the pulp is elfected with a catalyst, used at a concentration from 0.5 to about 3% by weight of the pulp, selected from the group consisting of barium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, alkali metal borates and titanium dioxide.
• a method for the delignification and bleaching of chemical and semichemical pulps which comprises delignifying and bleaching the pulp in an alkaline medium and including oxygen and a catalyst selected from the group consisting of barium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, alkali metal borates and titanium dioxide, said catalyst being in a concentration of from 0.5 to about 3% by weight of the pulp, said delignifying and bleaching being effected at temperatures in the range of from 90 to about 130 C. for a time of from half an hour to a few hours, the oxygen being present at a pressure in the range of 5-10 bars.
• a method for the delignification and bleaching of chemical and semichemical pulps which comprises delignifying and bleaching the pulp in an alkaline medium and including oxygen and a catalyst consisting of magnesium carbonate, said catalyst being in a concentration of from 0.5 to about 3% by weight of the pulp, said delignifying and bleaching being effected at temperatures in the range of from 90 to about 130 C. for a time of from half an hour to a few hours, the oxygen being present at a pressure in the range of 5-10 bars.
• Cited pulp hes a concentration of 6 to 10% and the alkali con- UNITED STATES PATENTS centration 1s 8 to 12% based on the pulp.

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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 (25)

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Citations (3)

• 1963
  • 1963-09-19 FR FR947956A patent/FR1387853A/fr not_active Expired
• 1964
  • 1964-09-10 US US395565A patent/US3384533A/en not_active Expired - Lifetime
  • 1964-12-22 OA OA50979A patent/OA00889A/fr unknown

Patent Citations (3)

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