US20020056533A1 - Method of treating chemical cellulose pulp - Google Patents

Method of treating chemical cellulose pulp Download PDF

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Publication number
US20020056533A1
US20020056533A1 US09/262,912 US26291299A US2002056533A1 US 20020056533 A1 US20020056533 A1 US 20020056533A1 US 26291299 A US26291299 A US 26291299A US 2002056533 A1 US2002056533 A1 US 2002056533A1
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chlorine dioxide
practiced
recited
pulp
treatment
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US09/262,912
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Tapani Vuorinen
Sari Juutilainen
Aki Vilpponen
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Andritz Oy
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Andritz Oy
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Application filed by Andritz Oy filed Critical Andritz Oy
Assigned to AHLSTROM MACHINERY OY reassignment AHLSTROM MACHINERY OY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: VILPPONEN, AKI, VUORINEN, TAPANI, JUUTILAINEN, SARI
Assigned to ANDRITZ-AHLSTROM OY reassignment ANDRITZ-AHLSTROM OY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: AHLSTROM MACHINERY OY
Assigned to ANDRITZ OY reassignment ANDRITZ OY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: ANDRITZ-ALSTROM OY
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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
    • D21C9/1026—Other features in bleaching processes
    • 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

Definitions

  • the invention relates to a method of treating chemical cellulose pulp from an alkaline pulping process in a chlorine dioxide stage which includes an acid treatment at a temperature of over 80° C.
  • Chlorine dioxide bleaching is a well-known and widely used bleaching procedure.
  • Conventional chlorine dioxide bleaching is usually performed at a temperature of 50-80° C. and a with a chlorine dioxide dosage of about 10-30 kg per ton of pulp.
  • Typical sequences used are, for example, D o ED 1 ED 2 and OD o ED 1 ED 2 and modifications thereof.
  • the treatment time in a D o stage is usually shorter than in other D stages, being for example, between about 30-90 minutes.
  • the pH of the pulp decreases to the range of 1-3 towards the end of the D o stage. In the D 1 and D 2 stages the treatment time is 2-3 hours and the pH a little higher than in the Do stage.
  • the chlorine dioxide stage (all types) is usually performed at a temperature of about 70° C., while the treatment time in the D o stage is 0.5-2 hours and in the D 1 and D 2 stages 2-3 hours. Higher temperatures than about 70° C. have typically been avoided as the low final pH in the range of 1-3 in the D stage combined with a high temperature and long treatment time deteriorates the strength properties of the pulp fibers.
  • Finnish patent application no. 944808 and WO publication no. 96/12063 disclose an acid treatment (A), also known as a hot acid step, method for pulp by which the consumption of chlorine dioxide can be reduced.
  • A removes hexenuronic acids, which can react with chlorine dioxide and thus increase chemical consumption, from the pulp.
  • the acids may be removed by adjusting the pH of the pulp to the range of 2-5, preferably between 2.5-4, and treating at a temperature of over 80° C., preferably between 90-110° C., at a time between 30-300 minutes.
  • the kappa number of the pulp is typically reduced by 2-9 units.
  • the present invention provides an alternative method of combining a hot acid step with a bleaching sequence utilizing chlorine dioxide.
  • the invention provides a method which may be practiced in an economical manner, particularly in bleaching plants of existing pulp mills. In other words, the invention is capable of fitting chlorine dioxide bleaching of pulp into a bleaching plant in an overall economical and environmentally acceptable manner.
  • the method of the invention is characterized in that the chlorine dioxide stage comprises successively at least a first chlorine dioxide step, and an acid treatment step, and that the pH of the first chlorine dioxide step is adjusted so that the final pH of the pulp in the first chlorine dioxide step is over 4.
  • the conditions during the first chlorine dioxide step are such that the hexenuronic acid groups in the pulp do not react with chlorine dioxide.
  • a D stage may comprise, successively, a D step and an A step.
  • the chlorine dioxide step of the DA stage is performed so as to have a final pH of over 4, preferably over 5.
  • the highest desirable pH value at the end of the first ClO 2 step is normally about 7.
  • the final pH of the first or the second chlorine dioxide bleaching stage is less than 4, typically 1-3.5.
  • hexenuronic acids do not react with chlorine dioxide at the pH range of over 4 and thus no chemical is consumed by reactions with chlorine dioxide. Chlorine dioxide is reduced to chlorite but it does not decompose further.
  • the chlorine dioxide dose in this step is about 0.1-1.5% active Cl (1-15 kg active Cl/admt), preferably between about 0.5-1.0% active Cl (5-10 kg active Cl/admt).
  • the conditions are typically as follows:
  • pH 2-5 preferably between 2.5-4;
  • the temperature in the D step of the DA stage is preferably over 70° C., preferably over 75° C., most preferably between 80-100° C., which is higher than the temperature of a conventional D stage.
  • the temperature in the D and the A steps is essentially the same and there is no special need to cool or to heat the pulp between the steps, which is advantageous for energy economy.
  • the invention is not limited to high temperature in the D step, but rather the D step may also be performed at the conventional D step temperature of below 70° C.
  • the treatment time in the D step of the invention is short, less than 10 minutes, preferably 30 seconds to 3 minutes.
  • the chlorine dioxide treatment time is over 30 minutes, even 120 minutes depending on the temperature and therefore a conventional D step requires its own reactor.
  • the DA stage according to the invention may be practiced by performing the acid treatment in a reactor tower but because of the short retention time the D step preceding the A step may take place, for example, in the feed line of the A step tower.
  • the pulp flowing in the line is heated to the desired temperature, for example about 90° C., and chemicals, such as chlorine dioxide, and alkali or acid if necessary to adjust the pH, are mixed into the pulp.
  • the pulp flows under these conditions for the required period, e.g. one minute, and subsequently, acid is added to the pulp and it is supplied into the acid tower.
  • the acid demand in the A step is reduced as the reactions of chlorine dioxide with the pulp lignin produce hydrochloric acid and organic acids as byproducts.
  • the chlorine dioxide stage as described above comprises in addition to the D and A steps described above a second D step, i.e. the chlorine dioxide stage comprises a first chlorine dioxide step, then a hot acid treatment step, and then a second chlorine dioxide step (DAD, or D/A/D).
  • the second ClO 2 step is performed in acidic conditions, in other words the pH may be less that 2 but preferably is between 2-4.
  • the pH may be less that 2 but preferably is between 2-4.
  • Adjustment of the temperature is not necessary, either, but rather the entire chlorine dioxide stage may be practiced essentially at the same temperature as the A step, and no special adjustments of the temperature are needed between the steps.
  • the treatment time in the second D step is preferably also short, less than 10 minutes, preferably 1-5 minutes, and it may be performed for example in the discharge line of the A step tower prior to the washer following the DAD stage.
  • Chlorine dioxide is added to the pulp flowing in the discharge line and the temperature and the pH are adjusted if necessary.
  • the required chlorine dioxide dose is typically 0.5-2.0% active Cl (5-20 kg active Cl/admt).
  • the acid treatment removes hexenuronic acids from the pulp and therefore the amount of chlorine dioxide chemical required in the second ClO 2 step is smaller than with pulp from which hexenuronic acids have not been removed.
  • the chlorine dioxide treatment may be considered to have been divided into two relatively short partial treatments. Both steps may be practiced at a high temperature; therefore the temperature and the treatment time must be chosen so as to cause as little viscosity loss in the pulp as possible. Two partial treatments contribute to a more homogenous brightness of the pulp than a single longer treatment.
  • the DA stage may be also practiced by chelating the pulp with EDTA, DTPA or a corresponding compound, after the A step in order to remove harmful metals; i.e. a DAQ stage may be utilized.
  • a DAQ stage may be utilized.
  • Providing a chelating treatment in connection with the DA stage is advantageous particularly if the bleaching sequence comprises a later bleaching stage with a chemical such as peroxide which is adversely affected by heavy metals.
  • the Q step may be performed at essentially the same temperature as the preceding D and A steps.
  • the pH may be in the range of 3-6.
  • the total amount of chlorine dioxide needed in the DA stage is not greater than the amount needed in an AD stage although the first D step is performed before the acid treatment.
  • the final pH of over 4 in the first D step prevents reactions between chlorine dioxide and hexenuronic acids.
  • a DA stage has produced pulp of at least as good quality as an AD stage.
  • a disadvantage of the AD stage may be the release of malodorous gases in the acid step if the pulp after washing still contains adequate amounts of sulfur compounds from digestion.
  • malodorous gases are oxidized by the bleaching chemical during the DA stage.
  • the method of the invention is applicable to chemical cellulose pulps manufactured by the sulfate process and other alkaline methods, which pulps typically contain hexenuronic acid compounds.
  • the pulp to be treated has preferably been oxygen delignified after digestion and before the chlorine dioxide stage.
  • the DA stage according to the invention may be at the beginning of the bleaching sequence, for example after oxygen delignification, or later in the sequence, for example after a peroxide stage. Therefore the invention is advantageously applied for example in connection with the following treatment/bleaching sequences or partial treatment/bleaching sequences:
  • E indicates an alkaline bleaching stage
  • OP or “PO” indicate a bleaching stage based on oxygen and/or peroxide, possibly at least part of the steps being pressurized and O indicating oxygen chemical and P peroxide, and the first letter in each step signifying the main effective bleaching chemical and the second letter, when used, designating a bleaching chemical supporting the bleaching reaction.
  • a method of treating chemical cellulose pulp from an alkaline pulping process e.g. the kraft process in a chlorine dioxide stage.
  • the method comprises: (a) In the chlorine dioxide stage, bleaching the chemical cellulose pulp in a first chlorine dioxide step, and adjusting the pH of the pulp in the first chlorine dioxide step so that the final pH of the step is over 4. And then, (b) in the chlorine dioxide stage effecting an acid treatment of the chemical cellulose pulp at a pH of between 2-5 and at a temperature of over 80° C.
  • (a) is practiced so that the final pH of the first chlorine dioxide step is over 5, and so that hexenuronic acid groups in the pulp substantially do not react with chlorine dioxide.
  • the temperature in the first chlorine dioxide stage is over 70° C., preferably over 75° C., and most preferably between about 80-100° C.
  • the treatment time in the first chlorine dioxide step is less than ten minutes, preferably between 30 seconds-3 minutes.
  • the chlorine dioxide dosage during the practice of (a) is preferably between about 0.5-1.5% active chlorine.
  • (b) is practiced so that the pH is between 2.5-4, the temperature is between 90-110° C., and the time is between 30-300 minutes, preferably pursuant to the formula described above. Since (a) and (b) are in the same stage there is no intermediate (i.e. between step) washing.
  • the method preferably further comprises (c) bleaching the chemical cellulose pulp, after (b), in a second chlorine dioxide step.
  • a)-(c) are practiced so that the treatment temperatures in the first chlorine dioxide step, the acid treatment step, and the second chlorine dioxide step, are substantially the same (between about 90-100° C., e.g. about 95° C.).
  • the treatment dosage is preferably between about 0.5-2.0%, and the temperature and time parameters are substantially the same as for the first chlorine dioxide step.
  • the method may also further comprise (d) treating the chemical cellulose pulp with chelating agent (such as EDTA, DTPA, mixtures thereof, or other chelating agents) after (a) and (b), especially if further treatment of the pulp is to be provided in a peroxide or other bleaching stage sensitive to the presence of metals. Also all of steps (a) through (c) may be practiced in a line leading up to an acid tower, in the acid tower, and in a line leading from the acid tower to a washer. All of the steps DAD of the stage are of course practiced without between step washing, inherent in the fact that they are part of the same stage.
  • chelating agent such as EDTA, DTPA, mixtures thereof, or other chelating agents
  • FIG. 1 schematically illustrates by way of example a preferred apparatus for carrying out the method of a preferred embodiment of the invention, that is treating cellulose chemical pulp from an alkaline process in a DAD stage.
  • chemical cellulose pulp e.g. produced by kraft pulping
  • a preceding treatment stage 10 by a high consistency pump 12 to an acid tower 18 .
  • the consistency of the pumped pulp is between about 6-25%, preferably between about 8-18%.
  • the preceding stage 10 may be a wash stage following digestion, or more often an oxygen delignification stage following digestion, or a wash following oxygen delignification.
  • Alkali or acid is added to the pulp in order to adjust the initial pH for the chlorine dioxide treatment or the first D step so that the final pH is over 4, preferably over 5, in order to prevent reactions between chlorine dioxide and hexenuronic acids.
  • the alkali and the chlorine dioxide may be added directly to the pump 12 as schematically illustrated in FIG. 1, or may be injected into duct 15 between the pump 12 and the tower 18 , or added to a conventional mixer 14 provided for this purpose.
  • the typical chlorine dioxide dosage added (e.g. at 12) is between about 0.5-1.5% active Cl.
  • Steam is preferably added to the pulp in order to raise the temperature typically up to 80-100° C. Steam may be added prior to the pump 12 in a conventional steam mixer (not illustrated) or mixed in the duct 15 following the pump 12 . Alternatively, the pulp may be heated indirectly in the duct 15 by a conventional heat exchanger (not shown).
  • the first D step is performed in the feed line 15 of the acid tower 18 while the pulp flows in the line 15 .
  • the treatment time in this step is typically between 30 seconds to 3 minutes.
  • the first D step is followed by an acid treatment in the tower 18 .
  • the pH of the pulp is adjusted (e.g. decreased), if necessary, to the level 2-5 required by the acid treatment in 18 by adding acid (sulfur acid, hydrochloric acid, waste acid from the production of chlorine dioxide, or any suitable organic acid) to the pulp in the mixer 14 .
  • acid sulfur acid, hydrochloric acid, waste acid from the production of chlorine dioxide, or any suitable organic acid
  • the temperature may be adjusted if necessary but according to the invention all the steps of the DAD stage are preferably practiced at about the same temperature, for example about 95° C., so that no special temperature adjustment is required between the steps.
  • the feed and flow of pulp to the acid tower 18 should be as even as possible by using a conventional distributor 16 or a doctor.
  • the distributor 16 is preferably as disclosed, for example, in U.S. Pat. No. 4,964,950, and its use for the above purpose is described in Finnish patent publication no. 94442. If the device 16 has adequate mixing properties and if desired, acid may be added to the device 16 and thus even avoid the use/purchase of the mixer 14 .
  • the top of the tower 18 is provided with a conventional discharger 20 or a discharge doctor to guide pulp to the discharge line 24 of the tower.
  • the second D step is performed in the discharge line 24 from tower 18 in order to bleach the pulp.
  • Chlorine dioxide may be added to the pulp via the acid tower discharger 20 or to a pump 22 in the discharge line 24 .
  • a separate mixer (not illustrated) may be provided in the line 24 for addition of chemical, preferably between 0.5-2.0% active Cl.
  • the addition of chemicals to the pulp is effected so that a proper treatment time for carrying out the second D step in the discharge line 24 is provided before the conventional washer 26 is reached.
  • the retention time is less than 10 minutes, preferably between about 1-5 minutes.
  • the treatment temperature of the second D step is preferably the same as that of the first D and A steps; thus no special adjustment of the temperature after the A step is needed here either.
  • pulp may be heated or cooled in a conventional heat exchanger (not shown) or by direct feeding of steam. A higher temperature (e.g. between about 75-110° C.) than conventionally is, however, required in order to obtain adequate bleaching during the short treatment time in line 24 .
  • the pH of the second D step is lower than that of the first D step.
  • the pH of the second D step in line 24 is between about 2-4; thus adjustment of the pH is usually not needed after the A step. If necessary, the chemical adjusting the pH may be added at the same time and place as the chlorine dioxide (e.g. in discharger 20 ).
  • Pulp was bleached in a DAD stage in the manner described above and subsequently the pulp was washed in the washer 26 and transported to further treatment.
  • the further treatment is an E stage.
  • the results of one example of this treatment are:
  • Oxygen-bleached initial pulp was tested in a laboratory, the kappa number of which was 11.9, viscosity 1061 ml/g and the ISO brightness 49.2%.
  • the pulp was treated with the following sequences:
  • the final bleached pulp had a viscosity of 868 ml/g, and a brightness of 89.9% ISO.
  • the same initial pulp was treated
  • the final bleached pulp had a viscosity of

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  • Engineering & Computer Science (AREA)
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US09/262,912 1998-03-06 1999-03-05 Method of treating chemical cellulose pulp Abandoned US20020056533A1 (en)

Applications Claiming Priority (2)

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FI980519A FI119383B (fi) 1998-03-06 1998-03-06 Menetelmä massan käsittelemiseksi
FI980519 1998-03-06

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US (1) US20020056533A1 (fi)
EP (1) EP0940498B1 (fi)
CA (1) CA2264423C (fi)
DE (1) DE69931295D1 (fi)
ES (1) ES2263236T3 (fi)
FI (1) FI119383B (fi)
PT (1) PT940498E (fi)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060118260A1 (en) * 2003-03-07 2006-06-08 Martin Ragnar Bleaching of cellulose pulp in a first chlorine dioxide bleaching step
US20060201642A1 (en) * 2005-03-08 2006-09-14 Andritz Inc. Methods of treating chemical cellulose pulp

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8920603B2 (en) 2006-10-11 2014-12-30 Akzo Nobel N.V. Bleaching of pulp
CA2665969C (en) * 2006-10-11 2016-04-12 Magnus Bjoerklund Bleaching of pulp

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6776876B1 (en) * 1994-10-13 2004-08-17 Andritz Oy Method of treating cellulosic pulp to remove hexenuronic acid

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5268075A (en) * 1989-10-19 1993-12-07 North Carolina State University High efficiency two-step, high-low pH chlorine dioxide pulp bleaching process
FI102301B1 (fi) * 1994-10-13 1998-11-13 Ahlstrom Machinery Oy Menetelmä selluloosamassojen käsittelemiseksi
FI105701B (fi) * 1995-10-20 2000-09-29 Ahlstrom Machinery Oy Menetelmä ja laitteisto massan käsittelemiseksi

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6776876B1 (en) * 1994-10-13 2004-08-17 Andritz Oy Method of treating cellulosic pulp to remove hexenuronic acid

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060118260A1 (en) * 2003-03-07 2006-06-08 Martin Ragnar Bleaching of cellulose pulp in a first chlorine dioxide bleaching step
US20060201642A1 (en) * 2005-03-08 2006-09-14 Andritz Inc. Methods of treating chemical cellulose pulp

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Publication number Publication date
EP0940498B1 (en) 2006-05-17
DE69931295D1 (de) 2006-06-22
CA2264423A1 (en) 1999-09-06
EP0940498A1 (en) 1999-09-08
PT940498E (pt) 2006-09-29
FI980519A (fi) 1999-09-07
CA2264423C (en) 2003-01-28
FI119383B (fi) 2008-10-31
FI980519A0 (fi) 1998-03-06
ES2263236T3 (es) 2006-12-01

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