EP0905307A1 - Procédé pour l'emploi de l'ozone dans un procédé de blanchiment de type ECF - Google Patents

Procédé pour l'emploi de l'ozone dans un procédé de blanchiment de type ECF Download PDF

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Publication number
EP0905307A1
EP0905307A1 EP98115927A EP98115927A EP0905307A1 EP 0905307 A1 EP0905307 A1 EP 0905307A1 EP 98115927 A EP98115927 A EP 98115927A EP 98115927 A EP98115927 A EP 98115927A EP 0905307 A1 EP0905307 A1 EP 0905307A1
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EP
European Patent Office
Prior art keywords
bleaching
pulp
ozone
stage
reaction
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.)
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Application number
EP98115927A
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German (de)
English (en)
Inventor
Jorge Luiz Colodette
Ana Campos H. De Brito
Marcelo Rodrigues Da Silva
Elias Salvador
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Praxair Technology Inc
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Praxair Technology Inc
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Publication date
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Publication of EP0905307A1 publication Critical patent/EP0905307A1/fr
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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
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/24—Continuous 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/26—Multistage processes
    • D21C3/263—Multistage processes at least one stage being in presence of oxygen
    • 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
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds

Definitions

  • This invention relates to a method for removing lignin from wood pulp, and more particularly to a method for bleaching lignocellulosic materials using ozone.
  • chlorinated substances are difficult to degrade naturally because they are comprised of carbon-carbon covalent bonds. From among a broad variety of these materials, the substances 2,3,7,8-tetrachlorodibenzofurane (TCDF) and 2,3,7,8-tetrachlorodibenzodioxine (TCDD) have shown to be bioaccumulative, potentially toxic and not environmentally sound.
  • TCDF 2,3,7,8-tetrachlorodibenzofurane
  • TCDD 2,3,7,8-tetrachlorodibenzodioxine
  • Ozone a three oxygen based compound, is a strong oxidative agent and highly reactive with lignin. It is first use as a bleaching agent for fibrous substances, including those used for the manufacture of paper, wherein the fibers are subjected to a chlorine dioxide and ozone gas mixtures. The first kraft pulp ozonolysis were effected in low and high consistencies and it was observed that the ozone dissolution in the fibrous suspension was a determining factor in the process. See, M. Byrd et al., "Delignification and bleaching of chemical pulps with ozone: a literature review", Tappi Journal, March 1992.
  • ozone stage has been shown to be useful in the bleaching sequence.
  • the ozone stage is preceded by a stage with oxygen, in alkaline medium, and followed by a simple alkaline extraction stage, or else the extraction supplied with oxygen, with peroxide or with oxygen and hydrogen peroxide.
  • the final bleaching can be effected by chlorine dioxide (ECF sequences) or hydrogen peroxide (TCF sequences) stages. See, Patent No. WO 91/18145 to B.F. Gregg et al.
  • U.S. Patent No. 4,959,124 to Tsai treats softwood kraft pulp with the steps of chlorine dioxide delignification (D), ozone bleaching (Z) and alkaline extraction (E, Eo, Ep, Eo).
  • This invention is directed to a ECF bleaching method for bleaching lignocellulosic materials comprising a bleaching sequence of at least three sequential stages, the stages including an oxidative treatment stage, an alkaline extraction stage, and an acidification bleaching treatment stage using ozone.
  • the oxidative treatment stage comprises a chlorine dioxide treatment employing a kappa factor between 0.05 and 0.40, with a pH of between from about 2 to about 5, at a reaction consistency in the range of from about 3% to about 15%, a reaction temperature of between about 20°C to about 90°C, and a reaction time of from about 10 minutes to about 180 minutes.
  • the alkaline extraction stage comprises an addition of an alkali source to render the pH of the reaction to above about pH 10, at a reaction time of from about 30 minutes to about 180 minutes, a reaction consistency range of from about 5% to about 15%, and a reaction temperature of from about 50°C to about 120°C.
  • the alkaline extraction stage comprises a treatment with oxygen having a dosage of from about 0.2% to about 1.2%, at a reaction pressure of from about 100 kPa to about 500 kPa.
  • the alkaline extraction stage also includes a treatment with peroxide having a dosage of from about 0.2% to about 1.5%.
  • the alkaline extraction stage further comprises addition of a magnesium having a dosage of from about 0.01% to about 0.2%.
  • the acidification bleaching stage comprises a treatment at a pH of from about pH 0 to about pH 5 using a mineral acid, the treatment having a reaction consistency of from 1% to about 15%, at a reaction temperature of from about 20°C to about 90°C, and a reaction time of from about 1 minute to about 60 minutes.
  • the ozone dosage ranges from about 0.1% to about 1.0% on a dry pulp basis.
  • the acidification bleaching treatment stage is followed by an alkaline treatment comprising an addition of an alkali source to render the pH of the reaction to about 11.0, the reaction time of from about 5 minutes to about 90 minutes, and the reaction temperature of from about 40°C to about 90°C.
  • the acidification bleaching treatment stage is followed by an alkaline treatment.
  • the alkaline treatment step may be preceded by an intermediate washing.
  • the acidification bleaching treatment stage further comprises addition of chlorine dioxide at a dosage of from about 0.1% to 3.0% on a dried pulp basis to achieve a desired brightness at a final pH of from about pH 2 to about pH 5.5, with a reaction consistency in the range of from about 1% to about 15%, at a reaction time of from about 30 minutes to about 300 minutes, in a reaction temperature of from about 30°C to about 90°C.
  • Two separate chlorine dioxide stages may be added.
  • a washing stage may take place between the chlorine dioxide stages.
  • An alkaline extraction stage may take place between the separate second chlorine dioxide extraction stages.
  • one or two hydrogen peroxide stages may be added instead of the final one or two chlorine dioxide stages.
  • the hydrogen peroxide in a dosage of from about 0.5% to about 3.0% on a dried pulp basis to achieve a desired brightness at a final pH in the range of from about pH 9.0 to about pH 12.0, with a reaction consistency of from about 5% to about 25%, at a reaction time of from about 30 minutes to about 240 minutes, and in a reaction temperature of from about 30°C to about 120°C.
  • the addition of a magnesium having a dosage of from about 0.02% to about 0.2%, on a dry pulp basis.
  • This invention is also directed to a ECF bleaching method for bleaching lignocellulosic materials comprising a bleaching sequence which includes a plurality of stages in sequential order, the stages including an oxidative treatment stage, an alkaline extraction stage and an acidification bleaching treatment stage using ozone.
  • the acidification bleaching treatment stage comprises an addition of ozone in a pulp ozonolysis step, at a reaction pH of from about pH 0 to about pH 5, a reaction consistency range of from about 0.1% to about 1.0% on a dry pulp basis, and a reaction temperature of from about 20°C to about 60°C.
  • this invention is directed to a bleaching method for ECF bleaching of lignocellulosic material comprising a bleaching sequence, the method comprising delignifying the lignocellulosic material using oxygen to form a delignified pulp; bleaching the delignified pulp with chlorine dioxide forming a bleached pulp; extracting the bleached pulp using an alkali source forming an alkaline extracted pulp; treating the alkaline extracted pulp with ozone in an acidic medium forming an ozone treated pulp; treating the ozone treated pulp with an alkali source; and bleaching the ozone treated pulp.
  • Another embodiment accounts for an intermediate washing prior to treating the ozone treated pulp with an alkali source.
  • This invention may be accomplished by pulp treatment with ozone after it has been oxidized with chlorine dioxide and extracted with alkali. After the ozone treatment, the pulp is extracted again with alkali and then bleached with chlorine dioxide until the desired brightness is achieved.
  • ozone does not react with previously oxidized lignin compounds which are extracted by the alkali, nor with a pulp having a high kappa number.
  • the ozone reacts more selectively with a pulp having a low kappa number which contains a residual lignin low in free phenolic structures. These structures are responsible for the low selectivity of the ozone bleaching, and the low phenolic character of the pulp arises from a previous treatment with chlorine dioxide followed by alkaline extraction.
  • This invention shows that ozone bleaching is most efficient when carried out after the pulp has been oxidized with chlorine dioxide and extracted with alkali. Moreover, the present invention contains an alkaline extraction step between the chlorine dioxide and the ozone stages. Thus, ozone would not have to react with chlorine dioxide degraded compounds and would more effectively react with a pre-bleached pulp having a low kappa number.
  • This invention relates to an ECF method for bleaching lignocellulosic material from hardwoods, softwoods, their mixture, or recycled fibers.
  • the proposed bleaching method is comprised of a number of steps, with possible variants in and between the steps.
  • the present invention allows employment of different types of lignocellulosic materials obtained by different types of pulping processes.
  • the lignocellulosic material may optionally be treated with oxygen prior to the bleaching method of this invention.
  • the first step which is optional, consists of a pulp delignification treatment with oxygen aiming at the maximum reduction in the residual lignin content without significantly impairing the cellulose chain degree of polymerization.
  • This treatment can vary from a simple and conventional oxygen stage to the utilization of double stages, also including the addition of chelation agents and hydrogen peroxide. To better understand this step, a more detailed description is described below:
  • the decrease of the kappa number of the pulp varies from about 40-50% for the systems (OO) and OQ(OP)
  • the second step of the process involves pulp treatment with chlorine dioxide at a medium consistency and in acid medium (pH ⁇ 4).
  • the amount of chlorine dioxide used in this process can be expressed by an index here named as kappa factor, which relates the kappa number of the unbleached pulp with the percent of active chlorine used in the referred stage.
  • this kappa factor can vary from 0.05 to 0.40, which will depend on the type of wood employed in the process for obtaining the pulp, the type of pulp, how and if the oxygen delignification was effected and the availability of chlorine dioxide.
  • This stage is represented usually in the industry by the symbol "D 0 " or "D 100 ".
  • This step can also employ molecular chlorine and chlorine dioxide mixtures, the combination being more effective for pulp delignification than chlorine or chlorine dioxide alone.
  • These mixtures can be effected in the forms: (DC), (CD) and (C+D).
  • the brightness achieved in this stage varies from 60 to 75% ISO, for kappa factors varying from 0.10 to 0.24, respectively.
  • the first chlorine dioxide stage can be replaced by a simple acidification or else by a chelation stage.
  • the third step includes an alkaline extraction stage (E) aiming at solubilizing the compounds oxidized in the chlorine dioxide stage. It has been suggested that a nucleophilic substitution caused by the alkaline stage is necessary to create new electrophilic attack sites in the remaining lignin structure. See, "The chemistry of delignification”. A general concept: Part II", J. Gierer, January, 1982, Holzaba .
  • This alkaline extraction stage can be proceeded with oxygen (Eo), hydrogen peroxide (Ep), or a combination thereof (Eop).
  • a fourth variant of the alkaline extraction is the pressurized processes, (PO), Pp or P HT , wherein elevated temperatures and greater dosages of oxygen and peroxide in relation to the Eop stage are generally used.
  • the kappa number varies from 2.0 to 7.0, the brightness from 70 to 80% ISO and the viscosity from 18 to 35 cP.
  • a fourth step of the present invention consists of an ozone treatment of the pulp in acid medium, under conditions that result in maximum decrease of the kappa number with a minimal degradation of the carbohydrates.
  • these conditions is the utilization of chlorine dioxide together with ozone, wherein a probable synergistic effect may occur due to the simultaneous action of both reagents.
  • Other conditions of optimization is the use of chelation agents for the control of metal profile, control of pH, pulp consistency, control of ozone concentration and gas/pulp contact efficiency.
  • a chelation agent for example oxalic acid, diethylenetetraamine pentaacetic acid (DTPA) or diethylenetriamine tetraacetic acid (EDTA), may be applied to the pulp to reduce the content of metals comprised therein.
  • DTPA diethylenetetraamine pentaacetic acid
  • EDTA diethylenetriamine tetraacetic acid
  • the pH of the pulp is preferably adjusted to a range between 0 and 5 before the application of ozone.
  • the consistency in which the ozone stage is carried out may be high, medium or low. High consistency is advantageous since it provides an efficient gas/pulp contact surface, in view of the fact that the pulp floccus are "fluffed" before the ozone delignification stage.
  • the drainage/pressing of the pulp to obtain the high consistency is considered to be a washing step, wherein the dissolved organic material may be recycled to the mill recovering plant.
  • the pulp obtained after the ozone stage may or may not be subjected to a rapid alkaline extraction to solubilize the compounds degraded during the reaction of lignin with ozone.
  • This pulp has a kappa number of less than 4.0, a brightness between 80-86% ISO and a viscosity between 13-25 cP.
  • This alkaline extraction can be effected with oxygen (Eo), peroxide (Ep) or oxygen plus peroxide [Eop, (PO), Pp or P HT ].
  • the sixth step and beyond are bleaching stages involving chlorine dioxide and/or hydrogen peroxide to achieve final brightness and viscosity of 86-90% ISO and 12-25 cP, respectively.
  • FIG. 4 shows the bleaching sequence 10 of DEo(ZE)D.
  • Pulp 20 from the post oxygen washer is fed into medium consistency pump 30, and is then passed into medium consistency mixer 32 with chlorine dioxide 62 prior to proceeding to D-stage 34. All the pumps and mixers referred to herein are of medium consistency.
  • the pulp is mixed with sodium hydroxide (and/or hydrogen peroxide) 64 prior to pump 38, and is then mixed with oxygen 66 in mixer 40 prior to the Eo (or Eop) extraction stage 42.
  • the pulp is mixed with sulfuric acid 68 and proceeds to pump 46 and mixer 48, where the pulp undergoes treatment with ozone 70.
  • the ozone treated pulp is then mixed with sodium hydroxide 72 and is transferred to extraction stage 52 via pump 50.
  • the pulp is then washed in washer 54 and pumped through pump 56 to mixer 58, where it is treated again with chlorine dioxide 74 in D-stage 60.
  • the resulting bleached pulp 76 is then passed to the final washer.
  • the pulp employed in this series of examples was obtained in a laboratory through the ITC (IsoThermal Cooking) process having a 17.3 kappa number, a 39.3% ISO brightness and a 78.2 cP viscosity.
  • the conditions employed in the bleaching steps for this series of examples are the following:
  • Table I A first comparison of the process of this invention with those from the art is shown in Table I. This table shows the results of final brightness and viscosity of the pulp, total dosage of chlorine dioxide, saving of chlorine dioxide in kg per kg of O 3 used and bleaching efficiency.
  • the process of this invention presented the greatest bleaching efficiency value (2.30%) among the sequences Z-ECF evaluated, being 26.4% and 16.8%, which are superior to the ones of examples 5 and 7, respectively.
  • an increase in the bleaching efficiency means that in order to achieve a similar final brightness a lower consumption of oxidative reagents occurred in the process of this invention in relation as compared to the conventional processes.
  • pulp employed in this series of examples was obtained in laboratory through the ITC process, having a 13.1 kappa number, a 45.4% ISO brightness and a 52.5 cP viscosity.
  • the conditions employed in the bleaching steps for this series of examples were the same as the previous series (examples 1 to 7), except by the pre-delignification stage with oxygen, which is described below:
  • Table II describes the results of final brightness and viscosity of the bleached pulp, total dosage of chlorine dioxide, saving of chlorine dioxide and bleaching efficiency for the process of this invention and the conventional processes.
  • Example 11 clearly shows greater efficiency as compared with the conventional process, with a saving of 1.20 kg of ClO 2 per kg of O 3 consumed.
  • the conventional as shown in examples 9 and 10 provides value for efficiency of 0.78 and 0.90, respectively.
  • the process sequence results in similar final brightness, consumes less ozone and/or chlorine dioxide as well as providing a high final viscosity in relation to the conventional process sequences.
  • the process sequence showed the greatest bleaching efficiency among the sequences Z-ECF.
  • the sequence of this invention DEop(ZE)D
  • example 8 is employed only as a reference since ozone is not used. It is important to emphasize that the use of the process of this invention resulted in an extremely low chlorine dioxide consumption in the entire process and this represents a great advantage from the viewpoint of closing the bleaching plant.
  • the pulp employed in this series of examples was obtained after a conventional delignification stage with oxygen on industrial scale, having a 9.5 kappa number, a 54.0% ISO brightness and a 26.5 cP viscosity.
  • the conditions used in the bleaching steps were similar to the previous series of examples, the only differences in the stages being described below:
  • Table III shows the results comparing the sequence of the present study with those of the art by treating an industrial kraft-O pulp. They show once more that the sequence DEop(ZE)D (example 16) is more efficient in the use of the oxidative reagents with reasonable values of bleaching efficiency, final brightness and viscosity.
  • the process of this invention required 59% less chlorine dioxide in relation to the reference sequence (example 12) resulting in a saving of 1.40 kg of chlorine dioxide/kg of O 3 consumed.
  • the conventional sequence (example 13) showed lower efficiency with a reduction of about 37% in the chlorine dioxide consumption.
  • the pulp employed in this series of examples was obtained after a conventional delignification stage with oxygen on industrial scale and presented a 10.6 kappa number, a 45.8% IS0 brightness and a 27.2 cP viscosity at the beginning of the experimentation.
  • the main difference in the procedure of this series of examples was the utilization of the pressurized peroxide (PO) bleaching instead of a simple oxidative alkaline extraction supplied with oxygen and peroxide, prior to the Z-stage.
  • the pulp treatment with pressurized peroxide was effected in a reactor at a consistency of 10%, pressure of 600 kPa with oxygen, temperature of 95°C and a reaction time of 120 minutes.
  • the charges used in the pulp were: 0.8% of hydrogen peroxide, 0.5% of O 2 , 1.6% of sodium hydroxide and 0.5% of magnesium sulfate.
  • Table IV shows how the industrial kraft-O pulp behaved in view of the different Z-ECF sequences. It can be noted that the ozone stage is at several positions in the sequences, wherein the two variants of the present invention (examples 20-23) showed the greatest final brightness. The low viscosity presented by example 20 was improved when a rapid and simple alkaline extraction was effected, immediately after the ozone stage (example 21).
  • a comparison of examples 22 and 23 shows that the pressurized peroxide stage is a good substitute for the alkaline extraction supplied with oxygen and hydrogen peroxide.
  • the examples shows the efficiency in the reduction of ozone charge applied to achieve the same brightness and a slightly superior viscosity.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
EP98115927A 1997-08-25 1998-08-24 Procédé pour l'emploi de l'ozone dans un procédé de blanchiment de type ECF Withdrawn EP0905307A1 (fr)

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US91723597A 1997-08-25 1997-08-25
US917235 1997-08-25

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EP0905307A1 true EP0905307A1 (fr) 1999-03-31

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EP98115927A Withdrawn EP0905307A1 (fr) 1997-08-25 1998-08-24 Procédé pour l'emploi de l'ozone dans un procédé de blanchiment de type ECF

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EP (1) EP0905307A1 (fr)
KR (1) KR19990023814A (fr)
CN (1) CN1209480A (fr)
BR (1) BR9803217A (fr)
CA (1) CA2245535A1 (fr)
ID (1) ID23571A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102995478A (zh) * 2011-09-09 2013-03-27 吉林化纤集团有限责任公司 一种制备高质量低污染竹材溶解浆的漂白方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111979822A (zh) * 2020-08-07 2020-11-24 齐鲁工业大学 一种适合无元素氯（ecf）短程序漂白的顺序漂白工艺

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4959124A (en) * 1989-05-05 1990-09-25 International Paper Company Method of bleaching kraft pulp in a DZED sequence
DE4039099A1 (de) * 1989-12-29 1991-07-04 Kamyr Ab Verfahren zum bleichen von cellulosebrei
WO1991018145A1 (fr) * 1990-05-17 1991-11-28 Union Camp Corporation Procede moins polluant de blanchiment de matieres lignocellulosiques
EP0511695A1 (fr) * 1991-04-30 1992-11-04 Eka Nobel Ab Procédé pour le blanchiment de pâte à papier contenant de la lignocellulose

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4959124A (en) * 1989-05-05 1990-09-25 International Paper Company Method of bleaching kraft pulp in a DZED sequence
DE4039099A1 (de) * 1989-12-29 1991-07-04 Kamyr Ab Verfahren zum bleichen von cellulosebrei
WO1991018145A1 (fr) * 1990-05-17 1991-11-28 Union Camp Corporation Procede moins polluant de blanchiment de matieres lignocellulosiques
EP0511695A1 (fr) * 1991-04-30 1992-11-04 Eka Nobel Ab Procédé pour le blanchiment de pâte à papier contenant de la lignocellulose

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102995478A (zh) * 2011-09-09 2013-03-27 吉林化纤集团有限责任公司 一种制备高质量低污染竹材溶解浆的漂白方法
CN102995478B (zh) * 2011-09-09 2015-04-15 吉林化纤集团有限责任公司 一种制备高质量低污染竹材溶解浆的漂白方法

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KR19990023814A (ko) 1999-03-25
CA2245535A1 (fr) 1999-02-25
BR9803217A (pt) 1999-11-03
CN1209480A (zh) 1999-03-03
ID23571A (id) 2000-05-04

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