EP0429767A1 - Délignification de fibres contenant de la lignocellulose - Google Patents

Délignification de fibres contenant de la lignocellulose Download PDF

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Publication number
EP0429767A1
EP0429767A1 EP90116168A EP90116168A EP0429767A1 EP 0429767 A1 EP0429767 A1 EP 0429767A1 EP 90116168 A EP90116168 A EP 90116168A EP 90116168 A EP90116168 A EP 90116168A EP 0429767 A1 EP0429767 A1 EP 0429767A1
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EP
European Patent Office
Prior art keywords
pulp
stage
chlorine
improvement
oxygen
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.)
Ceased
Application number
EP90116168A
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German (de)
English (en)
Inventor
Augustine Ivanhoe Dalton
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Air Products and Chemicals Inc
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Air Products and Chemicals Inc
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Publication date
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Publication of EP0429767A1 publication Critical patent/EP0429767A1/fr
Ceased legal-status Critical Current

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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
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
    • 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 is directed to improvements in processes for bleaching and delignification of wood pulp and other lignocellulosic material.
  • unbleached brown pulp (brown-­stock) from the pulp mill is directed to the bleach plant where it is subjected to a sequential series of alternating delignifying/bleaching and extraction steps, each stage involving distinctively different bleaching chemicals and/or process conditions.
  • the process objective of pulping is to chemically delignify wood or other lignocellulosic material (remove the lignin "glue” that binds the cellulosic fibers together)
  • the primary objective of bleaching is to whiten the pulp, albeit some residual delignification occurs.
  • the measure of effectiveness is the content of the remaining lignin and lignin residues, which is commonly expressed as the Kappa or permanganate number.
  • Kappa the content of the remaining lignin and lignin residues
  • bleaching one still determines the Kappa number, but the primary analytical parameters are the pulp brightness and viscosity.
  • bleach processes are chlorine-based.
  • a variety of sequences are used to bleach pulp to the desired target bright- ness levels, typically greater than 79 brightness units (ISO) and commonly 84-88.
  • the latter stages tend to involve milder, and more selective, and correspondingly more expensive bleaching agents like ClO2.
  • the more common bleach sequences use molecular chlorine, chlorine dioxide, or hypochlorite.
  • C C hlorination with chlorine (Cl2), commonly accomplished with co-addition (C D ) or pretreatment (D/C) with chlorine dioxide.
  • E Alkali E xtraction with NaOH.
  • E P or E O Peroxide or oxygen-reinforced alkali extraction.
  • D D ioxide treatment with chlorine dioxide (ClO2).
  • H Alkaline H ypochlorite bleaching, typically with sodium hypo­chlorite (NaOCl).
  • the actual sequence utilized by a given plant is a reflection not only of target brightness, but also local process economics, brownstock species, end use of pulps, and age of the bleach plant.
  • Chlorine reduction can also be achieved by substituting part of the chlorine requirements by high levels of chlorine dioxide in the chlorination stage.
  • oxygen prebleaching the chief advantage is that theoretically no significant capital is involved. However most mills do not have sufficient ClO2 capacity to handle the additional load.
  • one achieves the environmental objective of reduced chlorine consumption the chemical savings advantage of oxygen bleaching is lost since one is sub­stituting the considerably more expensive chlorine dioxide (45-50 /lb) for chlorine (8-10 /lb).
  • the increased consumption of chlorine dioxide may require investment in additional on-site dioxide generators since the dioxide is unstable and must be made on-site as needed.
  • E O Oxygen-reinforced alkali extraction
  • E O is now commonly practiced in most bleach plants.
  • E O is a relatively low capital, chemical cost-savings technology that simply involves mixing/injecting oxygen into the alkaline pulp of the first alkaline extraction stage which results in reduced chemical requirements in the subsequent bleach stages.
  • the reduced chemical require­ment to achieve brightness often allows the option of converting a five stage bleach processes to only three stages ("short sequence bleaching"); e.g., C D EDED ⁇ C D E O D (J. S. Enz, et al., TAPPI , 143 (1984) at optimal conditions of 60°C and 25 psig, an O2 contact time of no more than 5 minutes is required, and these systems are so designed.
  • E O technology is optimized for and directed to saving bleach chemicals in the subsequent (3rd stage and later) stages. Recently it was reported by Sjoblom, et al. (K. Sjoblom, et al., 1988 Int'l Pulp Bleaching Conference , pages 263-270) that a chlorine reduction in the chlorination stage could be achieved by increasing the dosage of the very expensive chlorine dioxide to the chlorination stage as previously disclosed by Annergren, et al., ( 1988 Int'l Pulp Bleaching Conference , page 37) and also modifying the E O stage conditions including increased temperature, pressure, oxygen contact time, added MgSO4 and optionally reinforcing the E O stage with hydrogen per­oxide.
  • Pulp brightness could be maintained only with increased chlorine dioxide dosages to the chlorination stage which was disclosed by Annergren, et al. 1988 Int'l Pulp Bleaching Conference , page 37, and also by Axegard ( TAPPI Journal , 54, October 1986). Even so, the utility of the described process is severely limited. To reduce required chlorine by this technology, an increase in bleach chemical costs is required as well as additional reinvestment in new E O process equipment to accommodate the required increased O2 reaction times and additional chlorine dioxide capacity. To reduce relatively inexpensive chlorine, as therein proposed, one must incur the costs of the considerably more expensive chlorine dioxide, hydrogen peroxide, MgSO4 and added capital equipment.
  • Among the objects of the present invention is to provide an improved bleaching process comprising a simple and easily implemented chlorine-­reduction technology that does not simultaneously require significant capital investment and which results in net chemical savings while achieving desired pulp brightness and strength (viscosity).
  • the required dosage/charge of chlorine and/or both chlorine and chlorine dioxide is reduced without detri­ment to final brightness and viscosity, by heating the pulp to 85-100°C and addition of a small amount of hydrogen peroxide to the pulp (without need of magnesium sulfate or other stabilizer) just prior to or directly after the addition of oxygen in the existing E O stage.
  • the process of the invention is applicable to treatment of lignocellulosic pulp in a multistage bleaching process comprising sequential chlorination and oxygen alkali extraction stages in which the chlorination stage optionally contains either or both chlorine (Cl2) and/or chlorine dioxide (ClO2), conventionally indicated as a C, C D or D/C stage.
  • FIG. 1 illustrates an embodiment of a conventional system employing a five-stage sequence for delignification and bleaching of wood pulp.
  • the illustrated system comprises 5 consecutive treating towers designated C (chlorination), E (alkali extraction), D (ClO2 treatment), followed by E and D.
  • C chlorination
  • E alkali extraction
  • D ClO2 treatment
  • the unbleached pulp is treated with Cl2, with or without ClO2 reinforcement in the first C tower.
  • the pulp enters at the bottom of the first C tower, flowing upwardly through the tower and discharging at the top of the tower into a washing section wherein it is washed with water.
  • the washed pulp is discharged from the washer via line 14, sodium hydroxide being added thereto.
  • Line 14 discharges the thus alkalized pulp into a steam mixer 15 by which it is brought to a temperature in the range of 40-70°C.
  • the thus heated pulp is pumped at 15 into the top of the E tower 16, where it is sub­jected to alkaline extraction followed by water washing as indicated at 18.
  • the washed pulp is then pumped, at 20, into the bottom of the first D tower 22 and flows upwardly through that tower in which it is treated with ClO2.
  • the pulp is again washed with water at 24 and pumped into the top of the second E tower 25 with addition of sodium hydroxide.
  • Discharged from the bottom of tower 25 the pulp is again washed in water at 26 and introduced into the bottom of the second D tower 28 for a second treatment with ClO2; the thus bleached pulp discharged from the top of tower 28 being water washed at 29.
  • the conventional 5 stage system (C D EDED) of Figure 1 is often replaced by a short three stage sequence (C D E O D); see Enz, et al., TAPPI Pro­ceedings, 1983 Pulping Conference, pages 309-313; Boussard, et al., op. cit., pages 315-317).
  • the three stage sequence without loss in pulp quality was made possible by introduction of molecular oxygen into the pulp entering the thus modified alkali extraction stage (“oxygen alkali extraction") designated by the symbol E O , illustrated in Figure 2, like parts bearing the same reference characters as in Figure 1 wherein applicable.
  • an O2/pulp mixer or O2 diffuser 30 is provided in the line feeding the E O tower.
  • a primary objective of the present invention is to enable reduction in the required amount of chlorinating agent needed to be employed in delignifi­cation and bleaching of lignocellulosic pulp to obtain the desired product without adverse effect on pulp brightness or viscosity, while avoiding the otherwise negative impact on environment of chlorine-based bleach plant ef­fluents.
  • Kappa factor The amount of molecular chlorine required for effective delignification of the pulp of a given Kappa number is expressed by the Kappa factor (KF), thus
  • a Kappa factor in the range of 0.21 to 0.23 is typically advocated and employed in mill practice, based on actual plant experience to provide a balance between suf­ficient delignification and minimizing subsequent/downstream chemical re­quirement to achieve target brightness.
  • C D E O D is representative of a common three-stage sequence with chlorine dioxide substituted for some chlorine in the chlorination stage as is common practice in the art and employing a conventional oxygen alkali extraction stage (3-5 minutes oxygen contact time, 20-25 psig, and 60-70°C). This is the reference sequence in which it is demonstrated that total chlorine charge (C+D) in the chlorination stage can be reduced by practice of the invention.
  • the oxygen reaction vessel was a direct steam-heated pressure vessel containing a removable rack upon which seven circular stainless steel mesh trays are arranged, one above the other.
  • the trays allow thin layers of pulp to be dispersed within the vessel so as to provide inti­mate contact with oxygen in order to simulate good O2/pulp contact available in the bleach plant.
  • Each individual pulp sample removed from the trays of the extraction reactor was subjected separately to different levels of dioxide charge in order to determine the bleaching performance profile, i.e., brightness vs. dioxide charge.
  • the extracted pulp sample was placed in a polyester bag and a calculated amount of aqueous chlorine dioxide added (usually 0.5 to 2.0% on pulp) followed by sufficient water to bring pulp consistency to 10%.
  • the bag was sealed and rapidly brought to 70°C and maintained at this temperature for 3 hours. At this time, typically an aliquot of bleach liquor was also removed and analyzed for residual dioxide. The dioxide bleached pulp was then treated with sulfur dioxide to bring the pH to 3 prior to forming handsheets for brightness measurements.
  • Results are graphically represented as brightness versus dioxide charge which is a measure of the ability of this sequence to achieve target brightness.
  • Kappa number (T236), viscosity (T230), handsheets (T218), and brightness (T217) determinations were made in accordance with the respective TAPPI Standard Test Procedure identified by the numbers in parentheses. Chem­ical charges are on a weight percent basis; pulp weight is reported on an air dry basis.
  • Examples 3-6 were performed as described in example 2 where the chlorine charge alone was reduced by 20% with the chlorine dioxide level maintained at the same (example 1) chlorination stage level so, in effect, to increase the dioxide substitution level to greater than the initial 15%. Otherwise, only the E O stage parameters were changed as described below, with the results compared in Table 2.
  • Ex. 3 graph 4c Extend O2 contact time of E O stage from conventional 5 to 20 minutes. 62.5 73.2 76.2 81.7
  • bar graphs 4a and 4b show the brightness of pulp after receiving treatment under conditions of Examples 1 and 2, respectively, (83.9 at full chlorine dosage and 73.4 at 20% reduction in chlorine dosage).
  • Bar graph 4c shows that the loss in brightness at lowered chlorine dosage is not compensated by extension of the time of exposure to added oxygen (Example 3).
  • Bar graph 4d shows that some further increase in brightness is had by raising the temperature of the E O stage to 100° or 110°C (Example 4) while maintaining the oxygen exposure at 20 minutes.
  • Example 5 (bar graph 4e) carried out at the conventional E O temperature (70°C) at extended time of O2 exposure (20 minutes) but with addition of hypochlorite to the E O stage does not achieve acceptable brightness.
  • Table 2 The results of Examples 3 to 6 are summarized in Table 2.
  • Example 7-8 Demonstration that Pulp Brightness can be Maintained with 20% Less Chlorine by Both Adding Peroxide and Increasing Alkaline Pulp Temperature Prior to Addition of Oxygen in the E O Stage
  • Example 9-11 Demonstration that the Pulp Properties of Brightness, Vis­cosity, Cleanliness, and the Quality of the E O Stage Effluent can be Maintained with a 30% Reduction in Chlorine and 100% Reduction/Elimination of Chlorine Dioxide in the Chlorination Stage (C D E O D vs. C ⁇ E O )
  • the desired reduced chlorination bleach process of the present invention can be achieved by reducing the needed chlorinating agent (molecular chlorine with or without chlorine dioxide) dosage to that required to maintain a Kappa factor in the range of 0.11 to 0.20, employing selected operating conditions not conventional in the oxygen alkali extraction stage (E O ) following the initial under chlorination at reduced KF, said conditions including:

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
EP90116168A 1989-11-17 1990-08-23 Délignification de fibres contenant de la lignocellulose Ceased EP0429767A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US43855189A 1989-11-17 1989-11-17
US438551 1989-11-17

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EP0429767A1 true EP0429767A1 (fr) 1991-06-05

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EP90116168A Ceased EP0429767A1 (fr) 1989-11-17 1990-08-23 Délignification de fibres contenant de la lignocellulose

Country Status (8)

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EP (1) EP0429767A1 (fr)
JP (1) JPH03161586A (fr)
BR (1) BR9004674A (fr)
CA (1) CA2023916A1 (fr)
FI (1) FI904662L (fr)
MY (1) MY106117A (fr)
NO (1) NO903893L (fr)
ZA (1) ZA907008B (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994011568A1 (fr) * 1992-11-13 1994-05-26 A. Ahlstrom Corporation Procede de blanchiment de pate de cellulose
WO2009005791A1 (fr) * 2007-06-29 2009-01-08 International Paper Company Procédé de blanchiment comportant au moins une étape d'extraction
SE2330103A1 (en) * 2023-02-24 2024-08-25 Valmet Oy Method and system for recycling textile material

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4568420A (en) * 1984-12-03 1986-02-04 International Paper Company Multi-stage bleaching process including an enhanced oxidative extraction stage
EP0206560A2 (fr) * 1985-06-17 1986-12-30 Pulp and Paper Research Institute of Canada Traitement alcalin au peroxyde et à l'oxygène pour des pâtes chimiques non-blanchies et chlorées

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6416958A (en) * 1987-07-13 1989-01-20 Toshiba Corp Apparatus for monitoring condition of waste liquid

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4568420A (en) * 1984-12-03 1986-02-04 International Paper Company Multi-stage bleaching process including an enhanced oxidative extraction stage
US4568420B1 (en) * 1984-12-03 1999-03-02 Int Paper Co Multi-stage bleaching process including an enhanced oxidative extraction stage
EP0206560A2 (fr) * 1985-06-17 1986-12-30 Pulp and Paper Research Institute of Canada Traitement alcalin au peroxyde et à l'oxygène pour des pâtes chimiques non-blanchies et chlorées

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994011568A1 (fr) * 1992-11-13 1994-05-26 A. Ahlstrom Corporation Procede de blanchiment de pate de cellulose
WO2009005791A1 (fr) * 2007-06-29 2009-01-08 International Paper Company Procédé de blanchiment comportant au moins une étape d'extraction
SE2330103A1 (en) * 2023-02-24 2024-08-25 Valmet Oy Method and system for recycling textile material
SE547843C2 (en) * 2023-02-24 2025-12-09 Valmet Oy Method for recycling textile material comprising cellulose

Also Published As

Publication number Publication date
JPH03161586A (ja) 1991-07-11
CA2023916A1 (fr) 1991-05-12
FI904662A7 (fi) 1991-05-18
NO903893D0 (no) 1990-09-06
FI904662L (fi) 1991-05-18
MY106117A (en) 1995-03-31
ZA907008B (en) 1992-05-27
FI904662A0 (fi) 1990-09-21
NO903893L (no) 1991-05-21
BR9004674A (pt) 1991-09-10

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