EP0561786B1 - Bleaching chemical pulp using chlorine/chlorine dioxide then ozone - Google Patents

Bleaching chemical pulp using chlorine/chlorine dioxide then ozone Download PDF

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Publication number
EP0561786B1
EP0561786B1 EP91916878A EP91916878A EP0561786B1 EP 0561786 B1 EP0561786 B1 EP 0561786B1 EP 91916878 A EP91916878 A EP 91916878A EP 91916878 A EP91916878 A EP 91916878A EP 0561786 B1 EP0561786 B1 EP 0561786B1
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EP
European Patent Office
Prior art keywords
pulp
chlorine
stage
ozone
chlorine dioxide
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP91916878A
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German (de)
English (en)
French (fr)
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EP0561786A4 (en
EP0561786A1 (en
Inventor
Ted Yuan Tsai
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International Paper Co
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International Paper Co
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    • 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
    • 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
    • D21C9/12—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
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone

Definitions

  • the present invention relates to delignification and bleaching of chemical Kraft cellulosic wood pulp fibers for use in papermaking and to the production of a pulp having reduced halogen concentrations, and good brightness and viscosity.
  • Chlorine-based chemicals such as chlorine, chlorine dioxide, and hypochlorite
  • Chlorine-based chemicals have been used in pulp bleaching for several decades, and continue to be used for removing lignin and bleaching the pulp to high brightness.
  • the extent of bleaching hence the degree of brightness obtained, is determined by the type of pulp being bleached and the proposed end use of the paper product.
  • kraft pulps intended for use in making fine writing papers require different bleaching circumstances which will produce the desired brightness in the final paper product.
  • chlorine-based bleaching agents have been employed in the prior art, there are produced chlorinated organics and organic halogens (i.e. chlorides).
  • the compounds are generally insoluble in an aqueous medium and substantial quantities are swept from the pulp with the effluent from one or more of the stages of the bleaching sequence. A relatively smaller percentage of such chlorinated organics and organic chlorides remain in the pulp and eventually appear in the paper product.
  • the "C” factor of the pulp is employed as a measure of the chlorination charge required for a specific pulp.
  • the "C” factor refers to the effective chlorination charge and is equal to the chlorine dioxide plus the chlorine in the charge (expressed in terms of effective chlorine), divided by the Kappa number of the pulp.
  • a "C” factor of 0.22 provides maximum brightness in a pulp without unacceptable degradation of the cellulosic fibers (e.g. reduced strength).
  • Another option to reduce the discharge of chlorinated organic compounds is to reduce the chlorine usage in the first stage of the bleaching process.
  • Two alternatives that produce no significant degradation of pulp properties have been commercialized for this purpose. These are (a) extended delignification in the cooking stage and (b) oxygen delignification. These alternatives, with proper extraction, reduce the lignin content of brown stock going into the bleach plant. They do not, however, reduce the chlorinated organic compounds in the bleached pulp and effluent to sufficiently low levels.
  • a third option to reduce the generation of chlorinated organics in a bleaching process is to substitute chlorine dioxide for chlorine.
  • Chlorine dioxide is a relatively strong oxidant compared to chlorine; to achieve the same degree of delignification, it requires only about thirty-eight weight percent chlorine dioxide on the pulp compared with one hundred weight percent of chlorine.
  • these prior art processes are of the DEDED type wherein the chlorination stage (D) is followed by the conventional extraction (E) and additional chlorination (D) stages.
  • the pulp and the discharge effluents resulting from this prior art option contain higher concentrations of chlorinated organics than are acceptable and/or desirable. Processes using both oxygen delignification and chlorine dioxide substitution have been suggested but do not achieve the regulated concentrations of chlorine-containing residues in either the pulp or the effluent.
  • the present invention comprises a method for the treatment of kraft pulp in preparation for its use in papermaking including the steps of
  • a chemical cellulosic wood pulp e.g. a kraft pulp
  • chlorine dioxide may initially contain up to about 50% chlorine, based on effective chlorine, or in this initial bleaching stage, up to about 50% chlorine may be added to the chlorine dioxide as a substitute for the chlorine dioxide, also based on effective chlorine.
  • the pulp is processed through an ozonation stage. After the ozonation stage, the pulp is processed through the customary extraction, further bleaching, etc. stages.
  • the ozonation takes place immediately following chlorination and prior to extraction. It has been recognized heretofore that ozone as a strong oxidant tends to degrade the pulp. Also, the art teaches that any use of ozone on pulp should be preceded with an acid wash, for example to remove heavy metals known to be harmful to the stability of ozone and/or decomposition products that may cause low pulp properties (e.g. strength). Contrary to such prior art, the present inventor has found that the ozonation can take place immediately following an initial chlorine dioxide/chlorine (D c ) bleaching stage as defined hereinabove.
  • D c initial chlorine dioxide/chlorine
  • the ozone treatment not only provides delignification and bleaching but also oxidizes substantial quantities of the chlorinated lignin residues left over from the chlorination stage.
  • This oxidative activity converts substantial quantities of the insoluble chlorinated organics to inorganic chlorine-containing compounds and/or to chlorinated organics that are soluble in the acid liquor present in the ozonation stage.
  • the oxidation of these chlorinated residues by the ozone thus not only reduces the chlorinated organic content in the wood pulp, but also reduces the adsorbed chlorinated organics discharged in the effluent.
  • These converted inorganic chlorides generally, are not environmentally hazardous and/or are recoverable.
  • TOCl total organic chloride
  • TOCl refers to the total organically bound chlorine content of the pulp resulting from the bleaching sequence unless indicated otherwise. TOCl is essentially insoluble.
  • the effluent discharge from the bleaching process of the disclosed method has less than 2.0 kg adsorbed organic halogens (AOX) per ton of wood pulp.
  • AOX adsorbed organic halogens
  • the pulp produced by the present invention has a brightness and viscosity that meet or exceed the requirements of industrial papermaking.
  • AOX adsorbed organic halides
  • FIGURES 1-5 are graphic representations, computer-generated from mathematical models depicting the relationship of ozone charge and chlorination factor in obtaining various values of the brightness, viscosity and total chloride on pulp.
  • an aqueous slurry of cellulosic wood fibers as is commonly produced by conventional digestion means in the papermaking industry is processed through sequential stages of a bleaching operation.
  • Softwoods, hardwoods or mixtures thereof may be processed employing the present invention.
  • the slurry preferably is processed directly to the bleaching sequence disclosed herein. If desired, it may be subjected to such treatment as oxygenation, ozonation or other oxidation prior to entering the present sequence, but with attendant increased expense.
  • the pulp slurry is treated with a chlorine-based agent, i.e. chlorine dioxide or a mixture of chlorine dioxide and chlorine.
  • a chlorine-based agent i.e. chlorine dioxide or a mixture of chlorine dioxide and chlorine.
  • the oxidant is principally chlorine dioxide.
  • D is employed to represent a bleaching stage employing chlorine dioxide.
  • D 1 is used to represent the first D stage of a sequence.
  • D c represents a stage employing chlorine dioxide plus chlorine.
  • the chlorine may be present in the chlorine dioxide, i.e. a mixture, or the chlorine dioxide may be first added to the pulp and after a brief time period the chlorine is added.
  • D ⁇ C is at times used to represent this latter chlorine substitution, but herein, the term D c is deemed to encompass both the mixture and the chlorine substitution procedures unless indicated otherwise.
  • the pulp of the present invention is processed through an ozonation stage, Z.
  • ozone tends to be decomposed by certain of the heavy metal components of the pulp that conventionally are removed by an additional acid treat; ment stage that comprises subjecting the pulp to an acidic medium.
  • the pulp moves from the D 1 stage which is an acidic stage directly to the Z stage without an acidic treatment stage.
  • the acid pulp is contacted with ozone in a reaction tower, for exam) ple, for a period of time and employing sufficient ozone to effect oxidation of substantial quantities of the chlorinated lignins and/or other chlorinated components of the pulp, in addition to the contribution of the ozone toward further delignification.
  • Many of the oxidized chlorine-based moieties are soluble in the environment of the Z stage. Thus, these oxidized chlorine-based moieties are solubilized into the liquor and extracted from the pulp during washing following the Z stage.
  • Other of the oxidized compounds are soluble in an alkaline solution such as is present in an E stage.
  • Extraction with an alkaline medium following the Z stage thus serves to remove alkaline-soluble oxidized chlorine-based moieties from the pulp.
  • a preferred complete sequence will include an extraction stage following the ozonation stage.
  • Such extraction stage may be enhanced with oxygen, E o , or peroxide, E p , a combination of oxygen and peroxide, E o+p , or other enhancer.
  • the pulp may be further processed through any of several selected stages.
  • the extraction stage is followed by a further bleaching stage. Chlorine dioxide, i.e. a D 2 stage is preferred as such further bleaching stage.
  • washes may be employed between selected stages, e.g. between the E and D 2 stages.
  • Southern softwood kraft pulp with Kappa number of 32.3 and an initial viscosity of 30.3 cP was used as the wood pulp slurry for all of the following Examples except as otherwise noted.
  • the series of Examples used various combinations of the following bleaching stages:
  • Examples 6-13 the pulp employed was the same as in Examples 1-5.
  • Examples 6-13 involved bleaching sequences using an ozone bleaching stage. Table 2 shows the properties of the pulps of these Examples.
  • Employing ozonation prior to chlorination Examples 6, 7, 10 and 12, produced pulps of low brightness, except in Examples 7 and 12 where additional and costly extraction and chlorine dioxide stages were added.
  • Examples 8 and 9 (DZED) employed 20% and 7% less chlorine dioxide than Example 11 (DZEDED) plus the fact that the DZED sequence with its fewer stages yielded better viscosity values and almost equal brightness values.
  • the brightness obtained by the DZED sequence is almost equal to the brightness obtained in the more costly prior art CEDED sequence (cf. Ex. 10 and Ex. 5).
  • the DZED (Ex. 8) produced better results than that of ZDED (Ex. 10) at same chemical charge.
  • the DZED produced 84.7% GZ brightness while ZDED produced only 79.0% GZ.
  • the same result has been experienced in the DZEDED (Ex. 11) and ZDEDED (Ex. 12) examples.
  • the DZ sequence also generated less TOCl than that of ZD sequence.
  • Examples 14-16 employed Southern softwood kraft pulp having a Kappa number of 27.3.
  • Table 3 shows certain properties of the resultant bleached pulps. From Table 3 it is noted that enhancement of the extraction stage (e.g. E o , p , or E o+p in the DZED bleaching sequence permits the use of less chlorine dioxide in the D stage and produces a pulp of substantially equivalent brightness and viscosity to the pulp produced using a DZED sequence without such enhancement.
  • E o , p , or E o+p in the DZED bleaching sequence permits the use of less chlorine dioxide in the D stage and produces a pulp of substantially equivalent brightness and viscosity to the pulp produced using a DZED sequence without such enhancement.
  • Examples 17-19 employed Southern hardwood kraft pulp having a Kappa of 14.9. Table 3 also shows the properties of the resultant bleached pulps of these examples. These pulps showed high viscosity and good brightness values as well as relatively low TOCl values employing total chlorine dioxide amounts less than the total chlorine dioxide amounts employed in obtaining substantially equivalent brightness and viscosity values for softwood pulp. For either softwood or hardwood pulps, the total chlorine dioxide employed in these Examples 14-19 is substantially less than the total chlorine dioxide employed to obtain equivalent brightness and viscosity values without employing ozone after chlorination.
  • Table 5 shows the adsorbed organic halogens (AOX) generated in the bleaching stages of the sequences of Examples 1-3, 9, 11 and 14.
  • Examples 1 and 2 showed AOX levels in excess of the desired 2.0 kg per ton of wood pulp.
  • a pre-delignification stage, as in Example 3, produced effluent within the 2.0 kg level, but Example 3 had high levels of chloride in the wood pulp (see Table 2).
  • Examples 9, 11 and 14 involved stages of chlorine dioxide bleaching followed by ozonation.
  • Example 9 represented a DZED sequence, and produced effluent well below the targeted AOX level.
  • Example 14 showed that pre-delignification with oxygen can improve the AOX level, but at the expense of the cost associated with the additional stage (O).
  • the present invention provides for a method of preparation of kraft cellulosic wood pulp fibers for use in papermaking that reduces the total chloride residue in the wood pulp to less than 200 ppm and the AOX discharge per ton of wood pulp to less than 2.0 kg.
  • the wood pulp has a brightness greater than 85% GE and a viscosity above about 14 centipoises.
  • the method is economical and readily adaptable to the current papermaking industry.
  • the percentage of ozone, based on oven dry weight of pulp, employed varies as a function of the "C" factor, the effective ratio of "C" factor to % ozone being between about 0.11 and 0.6, and preferably between about 0.2 and 0.6 for minimizing the TOCl and AOX values while maximizing the brightness and viscosity values of the pulp.
  • Example 6 there are shown the results of two runs in which the dioxin content of the pulp and effluent was determined.
  • Example 55 a control run indicative of prior art bleaching sequences that do not employ ozone, but which do include oxygen and peroxide enhanced extraction, there was no detectable tetrachlorodibenzodioxin (TCDD) in the final bleached pulp.
  • TCDD tetrachlorodibenzodioxin
  • TCDF tetrachlorodibenzofuran
  • the effluent from this run there was detected 2.5 ppt and 30.3 ppt of TCDD and TCDF, respectively,
  • Example 58 a D c ZE o D sequence in accordance with the present invention, there were no dioxins (TCDD or TCDF) detected in either the pulp or the effluent.
  • Table 7 presents the results of a bleaching sequence in accordance with the present invention in which the ozonated pulp at a pH of 12.7 was processed directly to an alkaline extraction stage (enhanced with oxygen) without an intervening water washing (ZE o ).
  • the GE brightness of the pulp and its viscosity were lower than when the pulp was washed with water between the Z and E stages, but these parameter values were still in a range that is acceptable for certain pulps.
  • the simplification of this process can lead to a capital reduction.
  • the TOCl of the pulp was 128 ppm, well below present regulated standards.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
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EP91916878A 1990-08-14 1991-08-14 Bleaching chemical pulp using chlorine/chlorine dioxide then ozone Expired - Lifetime EP0561786B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US56740990A 1990-08-14 1990-08-14
US567409 1990-08-14
PCT/US1991/005834 WO1992003609A1 (en) 1990-08-14 1991-08-14 Bleaching chemical pulp using chlorine/chlorine dioxide then ozone

Publications (3)

Publication Number Publication Date
EP0561786A1 EP0561786A1 (en) 1993-09-29
EP0561786A4 EP0561786A4 (en) 1995-11-15
EP0561786B1 true EP0561786B1 (en) 1997-11-26

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EP91916878A Expired - Lifetime EP0561786B1 (en) 1990-08-14 1991-08-14 Bleaching chemical pulp using chlorine/chlorine dioxide then ozone

Country Status (7)

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EP (1) EP0561786B1 (fi)
JP (1) JP3093263B2 (fi)
CA (1) CA2089477A1 (fi)
DE (1) DE69128287T2 (fi)
ES (1) ES2109273T3 (fi)
FI (1) FI930625A (fi)
WO (1) WO1992003609A1 (fi)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ZA93224B (en) * 1992-01-22 1993-08-18 Olin Corp Gas phase delignification of lignocellulosic material.
US6174409B1 (en) 1997-09-19 2001-01-16 American Air Liquide Inc. Method to improve final bleached pulp strength properties by adjusting the CI02:03 ration within a single (D/Z) stage of the bleaching process

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4568420B1 (en) * 1984-12-03 1999-03-02 Int Paper Co Multi-stage bleaching process including an enhanced oxidative extraction stage
US4959124A (en) * 1989-05-05 1990-09-25 International Paper Company Method of bleaching kraft pulp in a DZED sequence

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Publication number Publication date
CA2089477A1 (en) 1992-02-15
JP3093263B2 (ja) 2000-10-03
JPH06503857A (ja) 1994-04-28
FI930625A0 (fi) 1993-02-12
DE69128287T2 (de) 1998-03-19
FI930625A (fi) 1993-03-25
EP0561786A4 (en) 1995-11-15
DE69128287D1 (de) 1998-01-08
WO1992003609A1 (en) 1992-03-05
ES2109273T3 (es) 1998-01-16
EP0561786A1 (en) 1993-09-29

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