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
• • 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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
• • 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
  • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
• • 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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications

Definitions

• the present invention relates to a procedure for the bleaching of pulp, in which procedure the oxidating bleaching chemical is oxygen.
• Especially pulp obtained from a sulphate pulping process is of brown colour, which is mainly due to the lignin remaining in the pulp.
• Lignin is removed from the pulp by bleaching, which is a process consisting of several stages. During this process, the pulp is treated alternately with oxidizing, lignin-degrading chemicals and chemicals dissolving the degradation products. Oxidizing agents commonly used are oxygen and chlorine-containing chemicals, whereas alkali solutions are used for eliminating the degradation products.
• the spent bleach liquors causing the worst environmental pollution load are produced during the washing following the first chlorination and the first alkali treatment in the bleaching process.
• Various methods have been employed to reduce the pollution load, e.g. by replacing chlorine gas with chlorine dioxide or using oxygen as the oxidizing agent in the first bleaching stage, or by biological purification of the spent bleach liquor.
• the results achieved by these methods have not been completely satisfactory.
• Al though the amounts of chlorophenols and other toxic chlorine compounds in the spent bleach liquor have been significantly reduced by employing chlorine dioxide and oxygen bleaching, it has not been possible to achieve a sufficient reduction in the chemical oxygen demand values of the liquors. There­fore, the methods referred to have required the employment of efficient biological purification.
• the object of the present invention is to achieve a solution that enables the toxic content and the value of chemical oxygen demand of the spent bleach liquor to be reduced so as to reduce the need for purification of the liquor.
• the in­vention is based on oxygen bleaching and it is characterized in that oxygen is used in the first oxidation stage of the bleaching process, that the pulp is subjected to enzyme treatment, and that after the oxygen bleaching and enzyme treatment, the pulp is washed.
• enzyme treat­ment involves an essential reduction in the amount of toxic compounds in the spent bleach liquor while at the same time reducing its chemical oxygen demand, especially when the oxidizing chemical used in the first bleaching stage is oxygen.
• oxidizing chemical i.e. pure chlorine gas
• the pulp can be subjected to enzyme treatment and washing before the first oxidation stage.
• a preferable alternative solution is to carry out the enzyme treatment and washing after the first oxidation stage.
• the enzyme breaks down hemicellulose and/or lignin contained in the pulp and renders the pulp more spongy, thus enhancing the effect of the chemicals in subsequent oxida­tion and alkali treatment stages.
• the degradation products are removed and can be directed to incineration so that they will not contribute to the pollution load at all but are instead utilized in the energy handling system of the plant.
• the subsequent oxidation stages after oxygen bleaching can be implemented using a bleaching chemical containing chlorine, e.g. chlorine gas and/or chlorine dioxide.
• a bleaching chemical containing chlorine e.g. chlorine gas and/or chlorine dioxide.
• the production of detrimental chlorine compounds will thus be limited to these process stages, and to minimize the amounts of these compounds it is preferable to use chlorine dioxide to as large an extent as possible. This makes it possible to reduce the content of organic chlorine compounds in the spent bleach liquor by more than 70% even in the bleaching of softwood pulp. This is a result unattainable with previously known bleaching methods.
• the bleaching of pulp by the procedure of the invention can be performed by employing alternate oxidation and alkali phases and washing the pulp after each of these phases to remove the bleaching chemicals and degradation products.
• the enzyme treatment in the procedure of the invention is preferably carried out in a temperature range of 10-90 °C, the most suitable range being 40-80 °C, with pH values in the range 3.0-10.0, most suitably 4.0-8.0.
• the enzyme used can be a hemicellulase, cellulase, pectinase, esterase or a mixture of these.
• the invention also concerns the use of an enzyme in the bleaching of pulp, with oxygen used as the bleaching chemi­cal used in the first oxidation stage, and especially its use as a means of reducing the chlorine content of the spent bleach liquor when the bleaching chemical used in the first oxidation stage is oxygen and in subsequent oxidation stages a chemical containing chlorine, e.g. chlorine gas or chlo­rine dioxide.
• the enzyme is preferably a hemicellulase, cellulase, pectinase, esterase or a mixture of these, and it is used essentially in the manner explained in the above description of the bleaching procedure.
• a diluted enzyme mixture KD 50 (hemicellulase) was added to 220 g of dry matter obtained from pine sulphate pulp (with a dry matter content of 30%) so that a mixture with a consist­ency of 10% and a xylanase activity of 5 U/g of pulp dry matter was obtained.
• the temperature in the enzyme treatment was 55 °C and the duration of treatment 2 h.
• the pulp was subjected to preliminary oxygen bleaching.
• the acidity of the pulp was adjusted to pH 12.
• the temperature was 100 °C, overpressure 2 bar and duration of treatment 45 min.
• the pulp was washed in a Buchner funnel with a 20-fold amount of water.
• the pulp was subjected to an oxidizing bleaching treatment using a mixture containing 50 % chlorine dioxide and 50 % chlorine gas. Of this mixture, a dose equal to 2.0 x kappa number after oxygen bleaching was used. Treatment temperature was 40 °C and duration 45 min. After oxidation the pulp was washed in a Buchner funnel with a 20-fold amount of water.
• the mass was subjected to an alkali treatment using a 5 % sodium hydroxide solution in a dose of 0.9 x kappa. Con­sistency of solution was 10 %, treatment temperature 60 °C and duration of treatment 90 min. After the alkali treatment the pulp was washed in the same way as after oxidation.
• the bleaching was continued by repeating the oxidation and alkali phases and then once more the oxidation phase and washing the pulp between these phases as described above.
• the amount of chlorine dioxide in the second oxidation phase was 26 % and in the third phase 13 % of the amount of chlorine dioxide in the first oxidation phase.
• the dosage of sodium hydroxide was 1 % of the amount of chemical pulp.
• the liquids obtained from the washing stages phases after oxidation and enzyme treatment can be burned in a soda recovery boiler, in which case the amount of organic matter left in the spent bleach liquor is substantially smaller than in conventional chlorine bleach­ing and also smaller than in oxygen bleaching carried out without using an enzyme.
• Preliminary oxygen bleaching of 670 g of brown pine sulphate pulp was performed as follows: The pH value of the pulp was adjusted to 12 using NaOH, where­upon the pulp was subjected to a 45-min. oxygen treatment in an autoclave at a temperature of 100 °C and an oxygen over­pressure of 2 bar.
• the pulp was acidated with sulphuric acid to pH 6.
• An amount of diluted enzyme mixture (Trichoderma [r] hemicellu­lase MK 901, Cultor Oy) was then added to the pulp so that a mixture consistency of 10 % and xylanase activity of 5 U/g of pulp dry matter was obtained.
• the pulp was subjected to a 2-hour enzyme treatment at 55 °C.
• the pulp was subjected to an oxidating bleaching treatment using chlorine dioxide in a dosage of 6.6 % of pulp dry matter. Consistency of the mixture was 10 %, tem­perature during treatment 70 °C, and duration of treatment 180 min. After the treatment the pulp was washed in a Buchner funnel with a 20-fold amount of water.
• the pulp was treated with NaOH (amount of NaOH 1 % of the dry matter of the pulp) for 90 min. Viscosity of the pulp was 10 %. After treatment, the pulp was washed with a 20-fold amount of water.
• the pulp was subjected to a chlorine dioxide treatment.
• the dosage of chlorine dioxide was 3.3 % of pulp dry matter, mixture viscosity 10 %, treat­ment temperature 75 °C and duration 240 min. After treat­ment, the pulp was again washed with a 20-fold amount of water.
• Such a procedure allows the amount of organing chlorine compounds in the spent bleach liquor to be substan­tially reduced, even by more than 70 %. If the spent bleach liquors from all those stages which precede bleaching stages involving chlorine chemicals are subjected to burning, then the chemical oxygen demand of the spent bleach liquor will also be reduced by more than 50 %.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Biochemistry (AREA)
• Microbiology (AREA)
• Paper (AREA)
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• Cereal-Derived Products (AREA)
• Hard Magnetic Materials (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)
• Investigating Or Analysing Biological Materials (AREA)
• Table Devices Or Equipment (AREA)
• Bakery Products And Manufacturing Methods Therefor (AREA)
• Detergent Compositions (AREA)

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Publications (3)

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Cited By (19)

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• 1989
  • 1989-05-04 FI FI892151A patent/FI86896B/fi not_active Application Discontinuation
  • 1989-09-18 EP EP89117233A patent/EP0395792B1/de not_active Revoked
  • 1989-09-18 ES ES89117233T patent/ES2045320T3/es not_active Expired - Lifetime
  • 1989-09-18 DE DE8989117233T patent/DE68907593D1/de not_active Expired - Lifetime
  • 1989-09-18 AT AT89117233T patent/ATE91518T1/de not_active IP Right Cessation
  • 1989-09-18 NO NO893716A patent/NO172355C/no not_active IP Right Cessation
  • 1989-09-18 JP JP1241666A patent/JPH02293486A/ja active Pending
  • 1989-09-18 CA CA000611771A patent/CA1339593C/en not_active Expired - Fee Related

Non-Patent Citations (1)

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