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
  • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
• • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• This invention relates to a process for bleaching a chemical pulp.
• wood is converted into a pulp, usually by chemical means, and then spread on a wire to be dewatered to form the paper.
• Kraft pulping is the most widely practiced form of chemical pulping in North America. The pulp is relatively dark in colour and to produce a commercially acceptable paper, it is generally bleached before being formed into paper.
• bleaching agents include chlorine, chlorine dioxide, hypochlorites, hydrogen peroxide and oxygen. Typically, more than one of these chemicals is required and they are used singly or in admixture in sequence.
• the various bleaching compounds are designated by letter; chlorine is C, chlorine dioxide is D, caustic extraction is E,
• hypochlorite is H
• hydrogen peroxide is P
• oxygen is O
• the above compounds include chlorine and certain chlorine containing compounds and there are concerns about the use of chlorine and chlorine compounds in bleaching pulp.
• Chlorine and chlorine containing compounds react with pulp constituents - mainly lignin, fatty acids and resin acids - to produce chlorinated organic compounds.
• Some of these chlorinated organic compounds are of concern environmentally and some major pulp producing countries have restricted the amount that can be discharged from the bleaching process into waterways. It is reasonable to assume that most countries will introduce legislation restricting the discharge of such compounds.
• the elimination of elemental chlorine and its related compounds in the bleaching process would eliminate the production of chlorinated organic compounds in the effluent but efforts along this line have not been wholly effective.
• TCDD tetrachlorinated dioxins
• TCDF furans
• Oxygen delignification is a process of treating pulp under oxygen pressure, about 100 psig, at elevated
• the delignification process tends to produce weak pulp if delignification is extended too far - i.e. down to about 10 Kappa number.
• the Kappa number of a pulp is a measure of the bleachability of the pulp. It is a number indicating the number of milliliters of 0.1
• United States Patent 4,439,271 to O. Samuelson discloses a process using nitrogen dioxide pretreatment before oxygen delignification. The process retards the depolymerization of cellulose during oxygen bleaching. However, the emission of nitrogen-containing compounds from the bleaching effluent may pose another problem and these nitrogen compounds cannot be recovered by existing kraft pulping chemical recovery systems.
• U.S. Patent 4,404,061 to J.J. Cael discloses that pulps produced from a standard alkaline pulping process can be bleached with monoperoxysulphate to produce
• the dioxiranes are known compounds of the general structural formula:
• R 1 and R 2 may be aliphatic or aromatic groups and may be linked to form cyclic compounds.
• the dioxirane compounds and their preparation are described, for
• the present invention is a process for the bleaching of chemical pulps without use of elemental chlorine or by using elemental chlorine at a lower level than in the prior art, thus avoiding the production of the toxins TCDD and TCDF.
• the present invention is a process of bleaching a chemical pulp that comprises contacting the chemical pulp with a dioxirane.
• the dioxirane may be used with known bleaching agents either in combination or in sequence.
• the pulp is desirably one having a kappa number in the range of 15 to 60 if derived from a softwood species and 5 to 25 if derived from a hardwood species.
• the dioxirane is contacted with the pulp preferably at a temperature in the range of about 5° to 50°C for a time up to about 90 minutes.
• the dioxirane is used in amount sufficient to provide an active oxygen charge, i.e. one active oxygen atom per dioxirane molecule, of from 0.2 to 1.0% based on the oven-dried pulp.
• the dioxirane has the structure:
• R1 and R 2 which may be the same or different, is each an aliphatic or aromatic group and may be linked together to form a ring.
• One dioxirane compound that has proved useful is dimethyldioxirane but any dioxirane compound is appropriate, for example, those compounds where R 1 and R 2 are each alkyl groups with 1 to 4 carbon atoms. If a subsequent bleaching step is used, subsequent that is to the dioxirane treatment then, when the
• dioxirane-treated pulp has a residual lignin of less than 10 Kappa number, that subsequent bleaching of the pulp may be carried out by chlorine dioxide (D) alone or by the sequence chlorine dioxide, caustic extraction, chlorine dioxide (DED).
• D chlorine dioxide
• DED caustic extraction
• the sequence may be set out as D 1 ED 2 .
• Chlorine dioxide in the D 1 stage is used in the range 0.5 to 1%, preferably about 0.8%
• caustic in the E stage is in the range 0.2 to 0.7%, preferably about 0.4%
• chlorine dioxide in the D2 stage is in the range 0.2 to 0.7%, preferably about 0.4%. All the percentages are expressed as weight of oven-dried pulp. If chlorine dioxide alone is used, then it is in the range of 0.5 to 1% by weight of the oven-dried pulp, preferably about 0.8% of the oven- dried pulp.
• the subsequent bleaching may be carried out using the sequence: chlorine; caustic extraction; chlorine dioxide; caustic extraction; chlorine dioxide (CEDED).
• chlorine caustic extraction; chlorine dioxide (CEDED).
• stage C substantially reduced amount of chlorine charge is used in stage C, in stage E 1 the caustic charge is 60% of that in the C stage, in stage D 1 0.5 to 1.2% chlorine dioxide charge is used, in stage E 2 the caustic charge is 50% of that used in D 1 stage and in stage D2 0.25 to 0.6%
• chlorine dioxide charge is used. The percentages are based on the weight of oven-dried pulp.
• the chlorine used in the C stage is generally applied in combination with varying amounts of chlorine dioxide.
• Aspen pulp (50g oven-dried weight), produced by the kraft process to a Kappa number of 16.4, at 39% pulp consistency, was treated with the dimethyldioxirane (DMD) solution in acetone (280mL, 4.59g/L concentration, i.e.
• DMD dimethyldioxirane
• OCED OCED
• a third sample of the same aspen kraft pulp (50g oven-dried weight), was also bleached by a conventional process using a CED sequence. Elemental chlorine
• bleaching was carried out at 3% pulp consistency and 20°C for one hour using 3.3% available chlorine charge on oven-dried pulp, extraction at 74°C for two hours using sodium hydroxide (2.0% by weight on oven-dried pulp) at 12% pulp consistency, and chlorine dioxide (1.0% by weight on oven-dried pulp) delignification at 74°C for three hours at 6% pulp consistency.
• delignification has better mechanical properties than that treated with molecular oxygen to a level of 67% delignification. This fully bleached pulp at 86.8%
• Elrepho which was DMD-treated, has similar zero-span tensile strength to that of a pulp, at 89.9% Elrepho, bleached by a conventional CED bleaching process.
• a fourth sample of aspen pulp (50g oven-dried weight), produced by the kraft process to a Kappa number 16.4, at 39% pulp consistency, was treated with DMD solution in acetone (170 mL, 4.44g/L concentration, i.e. 0.33% active oxygen by weight on oven-dried pulp) and 80 mL of acetone at 25°C for three hours.
• This DMD treated pulp was filtered and washed with a large amount of distilled water.
• the resulting pulp was then further delignified with chlorine dioxide (1.0% by weight on oven-dried pulp) at 74°C for three hours at 6% pulp consistency, extracted with sodium hydroxide (0.72% by weight on oven-dried pulp) at 10% pulp consistency and 74°C for two hours , and bleached by another chlorine dioxide stage (0.5% by weight on oven-dried pulp) at 6% pulp consistency and 74°C for three hours.
• a fifth sample of the same aspen kraft pulp (100g oven-dried weight) was delignified by molecular oxygen at 12% pulp consistency using sodium hydroxide (4.0% by weight on oven-dried pulp), magnesium sulphate (0.5% by weight on oven-dried pulp), and molecular oxygen (100 psig) at 110°C for one and a half hours.
• This molecular- oxygen-delignified aspen pulp was further bleached with elemental chlorine (2% available chlorine by Weight on oven-dried pulp) at 20°C for one hour at 3% pulp
• a seventh sample of the same aspen kraft pulp (100g oven-dried weight) was delignified by molecular oxygen at 12% pulp consistency using sodium hydroxide (4% by weight on oven-dried pulp), magnesium sulphate (0.5% by weight on oven-dried pulp), molecular oxygen (100 psig) at 115°C for one and a half hours.
• the resulting oxygen- delignified pulp was thoroughly washed with a large amount of deionized water.
• Spruce pulp (50g oven-dried weight), produced by the kraft process to a Kappa number of 32, at 37% pulp
• a second sample of the same spruce kraft pulp (50g oven-dried weight) was also bleached by a conventional process using CED sequence. Bleaching with elemental chlorine was carried out at a 3% pulp consistency and 20°C for one hour using 6.4% available chlorine on oven-dried pulp, extraction at 12% pulp consistency and 74°C for two hours using sodium hydroxide (3.8% by weight on oven-dried pulp), and chloride dioxide (1% by weight on oven-dried pulp) bleaching at 6% pulp consistency and 74°C for three hours.
• Results shown in Table 4, illustrate that the DMD- treated pulp can be bleached to the same brightness as that bleached by a conventional process.
• the former uses a significantly reduced amount of elemental chlorine compared with that required by the conventional process.
• the present invention provides a process for treating pulp that can be subsequently fully bleached to 90% Elrepho, either without or with only small amounts of elemental chlorine.
• the DMD-treafeed pulps that have a residual lignin content corresponding to 5 Kappa number or less have pulp strengths equivalent to those of the untreated pulps.
• the fully-bleached pulps produced by the process of the invention have strength properties similar to those produced by conventional bleaching processes using high elemental chlorine charge.
• the bleaching of chemical pulps with the dioxirane compounds can be modified for a range of bleaching
• delignification being placed before or after the oxygen treatment.
• the use of two oxygen containing compounds can have the virtue of eliminating a wash step needed between stages of a sequence when chlorine and compounds of chlorine are used.
• the pulps used in this invention can be kraft, sulphite, soda, or other types of chemical pulps from hardwood and softwood species.
• the invention extends to chemical pulps and this term is intended to extend to pulps produced by the treatment of wood species with organic solvents to separate the wood components.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Compounds Of Unknown Constitution (AREA)
• Detergent Compositions (AREA)

Priority Applications (8)

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Publications (1)

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Cited By (3)

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• 1990
  • 1990-02-16 WO PCT/CA1990/000052 patent/WO1991012369A1/en active IP Right Grant
  • 1990-02-16 JP JP2503855A patent/JPH0718113B2/ja not_active Expired - Lifetime
  • 1990-02-16 BR BR909007993A patent/BR9007993A/pt unknown
  • 1990-02-16 AU AU51686/90A patent/AU641640B2/en not_active Ceased
  • 1990-02-16 EP EP90903735A patent/EP0515362B1/de not_active Expired - Lifetime
  • 1990-02-16 DE DE69008870T patent/DE69008870T2/de not_active Expired - Fee Related
• 1992
  • 1992-08-12 NO NO92923145A patent/NO923145L/no unknown
  • 1992-08-14 FI FI923644A patent/FI102195B/fi active

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