EP1101860A1 - Verfahren zum Bleichen von Pulpe mittels aktivem Ozon - Google Patents

Verfahren zum Bleichen von Pulpe mittels aktivem Ozon Download PDF

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EP1101860A1
EP1101860A1 EP00125129A EP00125129A EP1101860A1 EP 1101860 A1 EP1101860 A1 EP 1101860A1 EP 00125129 A EP00125129 A EP 00125129A EP 00125129 A EP00125129 A EP 00125129A EP 1101860 A1 EP1101860 A1 EP 1101860A1
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Prior art keywords
pulp
ozone
stage
dmso
bleaching
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English (en)
French (fr)
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Jorge Luiz Colodette (Engineer)
Ana Campos H. De Brito (Engineer)
Marcelo Rodrigues Da Silva (Engineer)
Elias Salvador (Chemist)
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Praxair Technology Inc
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Praxair Technology Inc
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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
    • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
    • 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
    • D21C9/101—Bleaching ; Apparatus therefor in solvent medium
    • 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
    • D21C9/142—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 in a multistage process involving ClO2/Cl2 exclusively
    • 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
    • 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 activated ozone.
  • chlorinated substances are difficult to degrade naturally because they contain carbon-carbon covalent bonds. From among a broad variety of these materials, the substances 2,3,7,8-tetrachloro-dibenzo-furane (TCDF) and 2,3,7,8-tetrachloro-dibenzo-dioxine (TCDD) have shown to be bioaccumulative, potentially toxic and not environmentally sound.
  • TCDF 2,3,7,8-tetrachloro-dibenzo-furane
  • TCDD 2,3,7,8-tetrachloro-dibenzo-dioxine
  • Ozone a three oxygen based compound, is a strong oxidative agent and highly reactive with lignin.
  • the first kraft pulp treatments 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.
  • U.S. Patent No. 4,959,124 to Tsai treats softwood kraft pulp with the steps of chlorine dioxide delignification (D), ozone bleaching (Z), alkaline extraction (E, Eo, Ep, Eo) and dissolution.
  • Ozone application according to all aforementioned bleaching methods suffers from two major drawbacks. These include: (1) low bleaching efficiency and (2) low bleaching selectivity with regard to pulp lignin.
  • the ozone bleaching efficiency defined as the units of kappa number dropped across the ozone stage per kilogram of ozone consumed, is usually too low to justify the high ozone bleaching cost.
  • the ozone bleaching selectivity defined as the ratio of units of kappa number per units of viscosity dropped across the ozone stage, is usually too low, thus impairing pulp quality.
  • the ozone consumption to reach a target kappa number is lower as compared to conventional ozone bleaching methods.
  • the final pulp viscosity of the ozone treated pulp obtained with the method of this invention is higher than that achieved with conventional ozone methods.
  • a method for bleaching lignocellulosic materials with activated ozone comprising a bleach sequence of at least four sequential stages.
  • the sequential stages include an oxidative treatment stage, an alkaline extraction stage, an activated ozone bleaching stage performed in the presence of a mixture of ethanol and dimethyl sulfoxide (DMSO) in appropriate proportions, and a final bleaching stage.
  • DMSO dimethyl sulfoxide
  • the oxidative treatment stage may be performed with chlorine, chorine dioxide, ozone, hydrogen peroxide, peracids or any other oxidant, under conditions that are well known to the skilled in the art.
  • the alkaline extraction stage may be performed with any source of alkali, preferably sodium hydroxide, under conditions conventionally used in the pulp industry.
  • the activated ozone bleaching stage comprises the acidification of the pulp with a mineral acid to render its pH to a value in the range of from about 1.5 to about 5, the treatment of the acidified pulp with an ethanol/DMSO additive mixture, the treatment of the additive treated pulp with ozone, and the subsequent neutralization of the ozone treated pulp with alkali to render the pulp pH to a value in the range of from about 5 to about 10.
  • the activated ozone bleaching stage is carried out at a reaction consistency of from about 1% to about 15%, at a reaction temperature of from about 20°C to about 90°C, and at a reaction time of from about 1 to about 120 minutes.
  • the mineral acid dose ranges from about 0.5% to about 4%
  • the ethanol dose ranges from about 0.001 to about 20%
  • the DMSO dose ranges from about 0.001 to about 8%
  • the ozone dosage ranges from about 0.1% to about 1.0%
  • the alkali dose ranges from about 0.5 to about 3%. All dosages are based on dry pulp fiber weight.
  • the activated ozone treated pulp is then washed and/or directly conveyed to the final bleaching operation, wherein it is further treated with chorine dioxide and/or hydrogen peroxide, in one or-more steps, under conditions conventionally known to the skilled in the art, to render a product of desired final quality.
  • "kappa number” shall mean the number of milliliters of a 0.1N KMnO 4 solution consumed by 1 gram of bone dry pulp and correlates with the pulp bleachability. Viscosity is an indirect measurement of the average degree of polymerization of the pulp cellulose chains and correlates with the pulp strength properties.
  • efficiency shall mean the number of kappa units (kappa numbers) dropped across the (ZE)-stage per kilogram of ozone applied (kg/t).
  • pulp kappa number shall mean the percent kappa number divided by the percent viscosity dropped across the (ZE)-stage.
  • the values of pulp kappa number, viscosity and brightness were measured according to Tappi standard procedures.
  • Figure 1 is a schematic representation of a sequence of bleaching stages that shows the preferred mode of activated ozone application according to the process of this invention.
  • This invention may be accomplished by pulp treatment with activated ozone after it has been treated with an oxidizing agent and extracted with alkali. After the activated ozone treatment, the pulp is bleached with chlorine dioxide and/or hydrogen peroxide until the desired brightness is achieved.
  • the ozone stage is activated with a mixture of organic solvents, namely, ethanol and dimethyl sulfoxide (DMSO) in appropriate proportions.
  • a mixture of organic solvents namely, ethanol and dimethyl sulfoxide (DMSO) in appropriate proportions.
  • ethanol/DMSO mixture act synergistically in the ozone stage improving both the efficiency and selectivity of ozone reaction with the pulp.
  • the role of the ethanol is to improve the efficiency of ozone bleaching by increasing the rate of lignin removal (kappa units removed/ mass unit of ozone consumed).
  • Ethanol functions as a free radical scavenger during ozone bleaching by capturing certain free radicals, namely hydroxyl and superoxide, which propagates ozone decomposition reactions. By capturing these free radicals, ethanol minimizes ozone losses in undesirable reactions, thus increasing overall process efficiency.
  • DMSO Dimethyl sulfoxide
  • DMSO has the property of both functioning as a free radical scavenger and increasing the uniformity of ozone contact with pulp fibers. Consequently, it protects pulp carbohydrates against degradation.
  • DMSO is known to disrupt the ordered water structure by breaking the intra-molecular hydrogen bonds and complexing with water. A change in water structure enhances the diffusion rate of ozone into the water and, consequently, reduces the build up of ozone concentration in localized areas.
  • the use of the organic solvent mixture (ethanol/DMSO) in the ozone stage has the unexpected effect of synergistically improving both efficiency and selectivity of the ozone stage at the same time.
  • the organic solvents must be added to the pulp together so that the synergistic effect can be obtained.
  • the treatment with activated ozone is preceded by oxidation and alkali extraction stages, said oxidation and alkali extraction stages being followed by pulp washing.
  • ozone does not react with previously oxidized lignin compounds that are extracted by the alkali, nor with a pulp having a high kappa number and a high content of transition metals that are partially removed in the oxidation stage.
  • the activated ozone reacts more efficiently and selectively with a pulp having a low kappa number that contains a residual lignin low in carry-over material and low in structures containing free phenolic units (or "phenolic lignin”).
  • Carry-over material is defined as non-oxidized and oxidized organic matter coming with the pulp from previous stages of the operation.
  • Phenolic lignin is defined as that fraction of the lignin incoming with the pulp that contains a free phenolic hydroxyl group. Both carry-over material and phenolic lignin are responsible for the low efficiency and selectivity of the ozone bleaching stage.
  • the low content of carry-over material and the low phenolic character of the pulp treated in accordance with the process of this invention arise from the fact that the pulp is previously treated with an oxidizing agent and alkali in separate stages.
  • This invention shows that the activated ozone bleaching stage is most efficient and selective when carried with a pulp that has been previously treated with an oxidizing agent and extracted with alkali.
  • This invention relates to a method for bleaching lignocellulosic material from non-wood fibers, hardwoods, softwoods, their mixture, or recycled fibers.
  • the proposed bleaching method is comprised of a number of stages with possible variants in and between the stages.
  • the present invention allows employment from different types of lignocellulosic materials obtained by different types of pulping processes.
  • the lignocellulosic materials may be treated with oxygen prior to the bleaching method of this invention. Oxygen treated lignocellulosic materials are actually preferred in relation to regular ones.
  • the first stage of the process involves pulp treatment in an oxidative stage with an oxidant that is aimed at dissolving transition metals, and attacking lignin containing free phenolics units (or phenolic lignin) and carry-over material incoming with the pulp from previous stages.
  • the second stage of the process involves pulp treatment in an alkaline extraction stage with any source of alkali.
  • This treatment aims at extracting and solubilizing the compounds oxidized in the previous oxidative 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.
  • the third stage of the process which is the novelty of the present invention, consists of an activated ozone treatment (aZE) of the pulp in acid medium, under conditions that result in maximum decrease of the pulp kappa number with a minimal degradation of its carbohydrates.
  • aZE activated ozone treatment
  • the ethanol/DMSO mixture acts synergistically so as to maximize ozone reaction with pulp lignin and minimize ozone reaction with pulp carbohydrates.
  • the activated ozone treatment stage is effected at a consistency of from about 1% to about 15% and a temperature of from about 20°C to about 90°C, for reaction periods of from about 1 to about 120 min, with ozone doses of from about 0.1% to about 1.0% based of pulp fiber dry weight.
  • the ethanol/DMSO mixture is added to the pulp immediately before ozone injection. Ideally, the two solvents should be added together as a mixture.
  • the doses of DMSO may vary in the range of from about 0.01% to about 8% based on pulp fiber weight and that of ethanol in the range of from about 0.01% to about 20%.
  • the pulp is neutralized with a suitable alkali source, preferably sodium hydroxide, to a pH in the range of from about 5 to about 10.
  • a suitable alkali source preferably sodium hydroxide
  • the activated ozone treated pulp is then subsequently bleached with chorine dioxide and/or hydrogen peroxide, to render a product of desired brightness.
  • chorine dioxide and hydrogen peroxide bleaching are well known to those skilled in the art.
  • FIG. 1 shows the bleaching sequence 10 of DEop(aZE)D.
  • the unbleached pulp 20 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 hydrogen peroxide 64 prior to pump 38, and is then mixed with oxygen 66 in mixer 40 prior to the Eop extraction stage 42.
  • the pulp is mixed with sulfuric acid 68 and proceeds to pump 46, where it receives the mixture ethanol/DMSO 70, and mixer 48, where the pulp undergoes treatment with ozone 72.
  • the activated ozone treated pulp is then mixed with sodium hydroxide 74 and is transferred to the neutralization tower 52 via pump 50, completing the (aZE)-stage.
  • the pulp is then washed in washer 54 and pumped through pump 56 to mixer 58, where it is treated again with chlorine dioxide 76 in D-stage 60.
  • the resulting bleached pulp 78 is then passed to the final washer.
  • Example 1 refers to a pulp treatment with 0.4% ozone based on pulp weight at 10% consistency, 30°C and pH 2.5, followed by alkali neutralization with 1.2% NaOH at 10% consistency, 60°C and 30 min, and pulp washing with excess distilled water. The combination of these chemical treatments is designated from here on as the (ZE)-stage.
  • Example 2 refers to the same treatments described in example 1, except that 10% of ethanol based on fiber weight was added in the ozone stage.
  • Example 3 was effected under the same conditions as example 1, except for the addition of 4% DMSO in the ozone stage.
  • Example 4 was performed similarly to example 1, except for the addition of a mixture of 10% ethanol and 4% DMSO in the ozone stage.
  • Examples 5-8 were done under the same conditions as example 4, except for the dosages of the ethanol/DMSO mixtures, which were varied in a wide range as shown in Table 1.
  • the results of the examples 1 to 8 were interpreted on the basis of (Z E )-stage efficiency and selectivity and final pulp brightness. The values of pulp kappa number and viscosity measured after the (ZE)-stage were used to calculate the values of efficiency and selectivity.
  • the gain in (ZE)-stage efficiency obtained with the mixture of ethanol/DMSO (57%) is higher than the sum of the gains achieved with ethanol alone (41%) and DMSO alone (11%) which adds up to only 52%.
  • the increase in selectivity derived from the use of the mixture of ethanol/DMSO (40%) is higher than the sum of the selectivity improvements caused by the ethanol (4%) or DMSO (29%) alone, which amounts to 33% only.
  • Examples 5 to 8 further shows that the (ZE)-stage efficiency, selectivity and brightness improvements derived from pulp treatment with ethanol/DMSO mixture prior to ozone treatment holds true even for additive doses much lower than those described in the example 4. However, the benefits of using the additive mixture tend to decrease as its doses are diminished.
  • Bleaching of chemical pulp is usually effected in a sequence of multiple stages.
  • the (ZE)-stage will normally be one of the stages of such a sequence. It is important to determine whether or not the enhanced efficiency, selectivity and brightness gain obtained in the (ZE)-stage, derived from the addition of the DMSO/ethanol mixture to the pulp prior to the ozone reaction, holds true when this stage is applied in a sequence of multiple stages. In other words, it is important to determine the impact of using such additive mixture in the ozone stage on the total bleaching chemical requirement and quality of the finally bleached pulp. This is demonstrated through examples 9 to 13 shown below.
  • the pulp sample employed in this series of examples was obtained from a kraft pulp mill, in the last washing stage after the oxygen delignification, having a kappa number of 9.1, viscosity 36.1 mPa.s and brightness 55% ISO.
  • the pulp was bleached using five different bleaching protocols.
  • Example 9 refers to the DEopDD ECF bleaching sequence that has been used commercially by many pulp mills (reference).
  • the first D-stage was carried out at 10% consistency, 60°C temperature, 30-min reaction and final pH 3.0 (adjusted with sulfuric acid).
  • the Eop-stage was carried with 1.1% NaOH, 0.5% O 2 and 0.5% H 2 O 2 based on fiber weight at 10% consistency, 200 kPa pressure, 90°C temperature, 90 min reaction and pH 11.0.
  • the second and third D-stages were carried out at 10% consistency, 70°C temperature, 180-min reaction and final pH 3.8 (adjusted with sodium hydroxide). Pulp washing between stages was effected with excess distilled water. Evaluation of pulp final brightness and viscosity was done according to Tappi standard procedures.
  • Example 10 refers to a bleaching sequence using ozone in the first stage of the process, (ZE)DEopD sequence.
  • the (ZE)-stage was performed with 0.4% ozone based on pulp weight at 10% consistency, 30°C and pH 2.5, followed by pulp treatment with 1.2% NaOH at 10% consistency, 60°C and 30 min, and pulp washing with excess distilled water.
  • the first and second D-stages and the Eop-stage were performed under the same conditions and using the same procedures described in example 9.
  • Example 11 refers to the same sequence of Example 10, except that the ozone treatment was activated with a mixture of ethanol/DMSO. All bleaching stage conditions were kept the same, except those of the (ZE)-stage where a mixture of 10% ethanol and 4% DMSO was added to the pulp slurry prior to the ozone treatment.
  • Example 12 refers to an ECF bleaching sequence using ozone in the third stage of the bleaching process, DEop(ZE)D sequence. This sequence is exactly the same as the one described in example 10, except for the fact that the (ZE)-stage was re-located from the first to the third stage of the sequence. All process conditions and procedures were kept the same as described for example 10.
  • Example 13 refers to the same sequence depicted in example 12, except that a mixture of ethanol/DMSO was added to the pulp prior to the ozone treatment.
  • the stage-by-stage conditions used in the various bleaching stages were the same as described for example 12. Effect of ozone stage activation with a mixture of ethanol/DMSO on overall performance of the sequences (ZE)DEopD and DEop(ZE)D applied to an oxygen delignified hardwood kraft pulp.
  • a comparison of examples 9 and 10 indicates that ozone application in the first stage of the ECF bleaching process decreases chlorine dioxide requirement in the order of 1.2 kg ClO 2 per kg of ozone applied. However, in this application mode ozone reduces pulp final viscosity (24%) in relation to the reference sequence, without ozone. On the other hand, if ozone is applied in the third stage, the replacement ratio of ozone for chlorine dioxide is substantially increased.
  • a comparison of examples 9 and 12 shows that each kg of ozone applied in the third stage displaces about 2 kg of chlorine dioxide. Furthermore, the viscosity penalty derived from the ozone treatment is much smaller in this case, being the final viscosity value only 12% lower than that of the reference.
  • examples 1-13 were applied to another type of lignocellulosic material.
  • a hardwood kraft pulp previously delignified with oxygen was used.
  • Examples 14 to 17 were carried out with an oxygen delignified softwood (spruce/pine) kraft pulp, which is more typical of North American pulp mills.
  • Example 14 refers to a pulp treatment with 0.3% ozone based on pulp weight at 10% consistency, 30°C and pH 2.5, followed by alkali treatment with 1.2% NaOH at 10% consistency, 60°C and 30 min, and pulp washing with excess distilled water. The combination of these two chemical treatments is designated from here on as the (ZE)-stage.
  • Example 15 refers to the very same treatments expressed in example 14, except that 10% of ethanol based on fiber weight was added to the pulp prior to the ozone treatment.
  • Example 16 was effected under the same conditions as example 14, except for the addition of 4% DMSO to the pulp prior to the ozone reaction.
  • Example 17 was performed similarly to example 14, except for the addition of a mixture of 10% ethanol and 4% DMSO to the pulp prior to the ozone treatment.
  • a comparison between examples 14 and 15 indicates that addition of ethanol to the ozone treatment substantially increases the efficiency of the (ZE)-stage while having only a slight effect on process selectivity.
  • a comparison between examples 14 and 16 shows that the addition of DMSO to the pulp prior to the ozone treatment increases (ZE)-stage selectivity substantially while slightly improving efficiency.
  • a comparison of examples 14, 15 and 16 with example 17 shows that the benefits of the ethanol and DMSO addition to the ozone stage are more than additive, suggesting that these additives act synergistically to improve ozone bleaching performance.
  • the benefits of adding the ethanol/DMSO mixture in the ozone stage of multiple-stage ECF bleaching sequences is shown in the examples 18 to 22.
  • the benefits of such a treatment are quantified by its impact of final pulp viscosity and total chlorine dioxide requirement to reach a target brightness of 90% ISO.
  • the softwood pulp (spruce/pine) sample employed in this series of examples was obtained from a kraft pulp mill, in the last washing stage after the oxygen delignification.
  • the pulp had a kappa number of 18.9, viscosity of 28.9 mPa.s and brightness of 28.0% ISO.
  • the pulp was bleached using five bleaching protocols.
  • Example 18 refers to the DEopDD ECF bleaching sequence that has been used commercially by many pulp mills.
  • the first D-stage was carried out at 10% consistency, 60°C temperature, 30-min reaction and final pH 3.0 (adjusted with sulfuric acid).
  • the Eop-stage was carried with 1.1% NaOH, 0.5% 02 and 0.5% H202 based on fiber weight at 10% consistency, 200 kPa pressure, 90°C temperature, 90 min reaction and pH 11.0.
  • the second and third D-stages were carried out at 10% consistency, 70°C temperature, 180-min reaction and final pH 3.8 (adjusted with sodium hydroxide). Pulp washing between stages was effected with excess distilled water. Evaluation of pulp final brightness and viscosity was done according to Tappi standard procedures.
  • Example 19 refers to a bleaching sequence using ozone in the first stage of the process, (ZE)DEopD sequence.
  • the (ZE)-stage was performed with 0.3% ozone based on pulp dry weight at 10% consistency, 30°C and pH 2.5, followed by alkali treatment with 1.2% NaOH at 10% consistency, 60°C and 30 min, and pulp washing with excess distilled water.
  • the first and second D-stages and the Eop-stage were performed under the same conditions and procedures as described for example 18.
  • Example 20 refers to the same sequence of example 19, except for the fact that a mixture of 10% ethanol and 4% DMSO was added to the pulp slurry prior to the ozone treatment. All other bleaching conditions were kept the same as described in example 19.
  • Example 21 refers to an ECF bleaching sequence using ozone in the third stage of the bleaching process, DEop(ZE)D sequence. This sequence is exactly the same as the one described in example 19, except that the ozone treatment was re-located from the first to the third stage of the sequence. All process conditions and procedures were kept the same as described for example 19.
  • Example 22 refers to the same sequence depicted in Example 21, except that a mixture of 10% ethanol and 4% DMSO was added to the pulp slurry prior to the ozone treatment.
  • the stage-by-stage conditions used in this sequence were the same as in example 21. Effect of ozone stage activation with a mixture of ethanol/DMSO on overall performance of the sequences (ZE)DEopD and DEop(ZE)D for an oxygen delignified softwood kraft pulp.
  • a comparison of examples 18 and 19 indicates that ozone application in the first stage of the ECF bleaching sequence, for the softwood pulp, decreases chlorine dioxide requirement in the order of 1.87 kg ClO 2 per kg of ozone applied. However, in this application mode ozone causes a penalty on pulp viscosity of about 28%, in relation to the reference sequence without ozone. On the other hand, if ozone is applied in the third stage the replacement ratio of ozone for chlorine dioxide is substantially increased.
  • a comparison of examples 18 and 21 shows that each kg of ozone applied in the third stage displaces about 2.63 kg of chlorine dioxide. Furthermore, the viscosity penalty derived from ozone application in the third stage is much smaller, being only 5% lower than that of the reference.
  • the results for the softwood kraft pulp sample also indicate that proper location of the Z-stage in the bleaching sequence has a significant impact on overall efficiency and selectivity of the bleaching process.

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  • Wood Science & Technology (AREA)
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EP00125129A 1999-11-19 2000-11-17 Verfahren zum Bleichen von Pulpe mittels aktivem Ozon Withdrawn EP1101860A1 (de)

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KR (1) KR20010051774A (de)
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CN104790241A (zh) * 2015-05-12 2015-07-22 四川理工学院 一种高纯度高质量竹材溶解浆的清洁制备方法
CN105839449A (zh) * 2016-04-07 2016-08-10 四川理工学院 一种粘胶级竹浆粕的清洁制备方法
CN110656527A (zh) * 2019-09-12 2020-01-07 华南理工大学 一种臭氧和二氧化氯协同高效漂白中浓纸浆的方法及装置
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RU2724362C1 (ru) * 2019-07-04 2020-06-23 Федеральное государственное бюджетное образовательное учреждение высшего образования "Санкт-Петербургский государственный университет промышленных технологий и дизайна (СПбГУПТД)" Способ отбелки целлюлозы
CN110656527A (zh) * 2019-09-12 2020-01-07 华南理工大学 一种臭氧和二氧化氯协同高效漂白中浓纸浆的方法及装置

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