EP0919661A1 - Procédé de blanchiment au péroxyde de substances cellulosiques et lignocellulosiquesm - Google Patents

Procédé de blanchiment au péroxyde de substances cellulosiques et lignocellulosiquesm Download PDF

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Publication number
EP0919661A1
EP0919661A1 EP98204179A EP98204179A EP0919661A1 EP 0919661 A1 EP0919661 A1 EP 0919661A1 EP 98204179 A EP98204179 A EP 98204179A EP 98204179 A EP98204179 A EP 98204179A EP 0919661 A1 EP0919661 A1 EP 0919661A1
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Prior art keywords
pulp
bleaching
stage
peroxide
hydrogen peroxide
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EP98204179A
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German (de)
English (en)
Inventor
Lewis D. Shackford
William J. Miller
Brian P. Roy
Barbara Van Lierop
Richard M. Berry
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Pulp and Paper Research Institute of Canada
Beloit Technologies Inc
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Pulp and Paper Research Institute of Canada
Beloit Technologies Inc
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Application filed by Pulp and Paper Research Institute of Canada, Beloit Technologies Inc filed Critical Pulp and Paper Research Institute of Canada
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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
    • D21C9/1057—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
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

  • This invention pertains, generally, to the bleaching of lignocellulosic material in the pulp and paper industry and, in particular, to a process to improve the performance of a pulp bleaching sequence which uses hydrogen peroxide. It is especially valuable when used in conjunction with a bleaching sequence designed for the production of pulps bleached without the use of chlorine compounds.
  • Hydrogen peroxide is an oxidizing chemical, commonly used in the brightening of mechanical, semimechanical, semichemical, and recycled pulps. It is also used in chemical pulp bleaching to aid in delignification.
  • the Pulp & Paper Research Institute of Canada has developed several novel ways to bleach mechanical pulps.
  • the high temperature peroxide system disclosed by Lierbergott, et al. is of interest because it pursues the same brightness development as conventional high consistency bleaching systems, but does so at medium consistency (10-14%). This is achieved by increasing the temperature of the pulp to about 85°C and lowering the pH, which is differentiated from conventional high consistency peroxide systems. Because of the faster reaction resulting, the retention time is reduced from hours to minutes (15-30 min.), and no silicate is required to stabilize the peroxide solution. The peroxide charge remains about the same as that of the conventional systems.
  • a high temperature peroxide system has been proposed in a copending application of Bottan, G. to be operated at 85-95°C. for very short periods of time. No one has yet proposed to superheat pulp and to operate a peroxide stage under pressure at short retention times in excess of 100°C. It is desirable to minimize the pulp retention time in order to minimize the capital investment required, while maintaining brightness similar to that which can be achieved using very long retention times.
  • Reactivation of Residual Peroxide has been proposed by Anthony Lachenal of the Centre Technique du Textil in Grenoble, France for use in the bleaching of mechanical pulps.
  • This allows the reactivation of the non-consumed (or residual) peroxide (after the first reaction stage tower) by increasing the alkalinity of the pulp suspension.
  • the aim is to eliminate expensive dewatering equipment normally used after the bleaching tower to recover the residual peroxide and to recirculate it to the point of addition of the fresh peroxide (usually at a mixer before the bleaching tower).
  • This proposal becomes important when compared with a conventional two stage peroxide bleaching system which requires the expensive dewatering equipment between stages.
  • the first stage reaction takes place for several hours in a conventional tower at 60°C., prior to reactivation of the residual peroxide.
  • Caustic is then added in quantities proportional to the peroxide residual obtained after several hours of reaction at 60°C.
  • hydrogen peroxide has been primarily used in medium consistency systems, in which the pulp slurry, from a previous stage, is dewatered in a thickener or washer to about 10-14% consistency.
  • the peroxide solution is conventionally added, together with alkali, at the repulper (discharge from the thickener or washer) or before the medium consistency tower in a medium consistency pump or mixer.
  • Hydrogen peroxide is also used in the final stages of pulp bleaching to achieve a high brightness stable bleached pulp.
  • Use of hydrogen peroxide in bleaching of pulps has been limited to temperatures typically less than 90°C., as it has been believed that the peroxide would decompose, resulting in very poor utilization of the bleach chemical, reduced pulp strength, and poor economics of bleaching.
  • the use of hydrogen peroxide under conditions of high temperature and relatively long retention time has been proposed as a means for developing very high brightness pulps, when used at the end of a conventional or chlorine free bleaching sequence.
  • the required retention time is 1-3 hours. It has been shown that pressurized oxygen peroxide systems at long retention times can increase the brightness ceiling of the pulp over what can be obtained using conventional atmospheric peroxide bleaching stages. It is desirable to minimize the required retention time under pressure in order to reduce the capital investment required for the installation. For example, according to the prior art, the use of 100+°C. for 1-3 hours has been demonstrated in the laboratory to be very effective in reducing the amount of time required for the peroxide bleaching process. It seems though, that the economics may not be very attractive for this process as the capital required for a 1-3 hour pressurized peroxide stage is quite high.
  • EP-A-0 285 530 discloses a short peroxide bleaching step under pressure at a temperature greater than 100°C. This document teaches that this single peroxide bleaching process occurs at a pH of at most 9 and additionally teaches that a high efficiency washing step should follow the short pressurized bleaching reaction.
  • a method for using hydrogen peroxide for bleaching cellulosic and lignocellulosic pulp in a three stage bleaching sequence comprises the steps of adjusting consistency of the pulp to 10% - 18% and introducing the pulp to a mixer in which sodium hydroxide is added to bring the pulp to a pH of greater than 8.5; adding hydrogen peroxide to equal from 0.5%-5.0%, by weight, of the pulp; heating the pulp to a temperature greater than 100 degrees Celsius while maintaining sufficient pressure to prevent boiling of pulp liquor; passing the pulp through a reactor column at a rate which provides a reaction time in the column of less than 45 minutes; cooling the pulp without adding additional hydrogen peroxide and discharging the cooled pulp to a washer, in which a substantial portion of the unconsumed bleaching chemicals and dissolved material is removed from the pulp, and in which the pulp consistency may be adjusted to a preferred value for a second stage of bleaching treatment.
  • the second bleaching stage comprises the steps of adding sufficient alkali or acid to adjust the pH of the pulp to a preferred value for the bleaching chemical; introducing the pulp to a mixer in which the second bleaching chemical is mixed with the pulp; discharging the pulp from the mixer into a reaction vessel in which the pulp is held for a sufficient time to permit consumption of a substantial portion of the applied chemical; discharging the pulp from the reaction vessel to a washer, in which a substantial portion of the unconsumed bleaching chemicals and dissolved organic material is removed from the pulp and in which the pulp consistency is adjusted, if necessary, to 8%-18%.
  • the pulp is exposed to a third stage of bleaching treatment, the third stage treatment comprising all steps identical to those recited for said first stage hydrogen peroxide bleaching treatment subsequent to adjustment of pulp consistency.
  • one step of high temperature peroxide bleaching under pressure in accordance with the first stage is combined with a second step of peroxide bleaching by reactivating residual hydrogen peroxide.
  • the second step of peroxide bleaching includes the steps of introducing the pulp to a mixer and while a significant residual of hydrogen peroxide remains in the pulp; adding a second quantity of alkali for reactivating residual hydrogen peroxide and sufficient to bring the pulp to a pH of at least 9; and depositing the pulp from the mixer in a reaction tower and allowing the reaction to proceed for a sufficient time to permit consumption of a substantial portion of the residual hydrogen peroxide.
  • pulp from a conventional washer or thickener is discharged through pipe 10 into mixer 100, where steam for heating the pulp and alkali for increasing the pH of the pulp is added through pipe 15.
  • the pulp is heated and adjusted to a pH of more than 8.5, preferably 9.5-10.5.
  • the heated and pH adjusted pulp is discharged from mixer 100 through pipe 20 to a conventional medium consistency pump 200 which pumps the pulp through pipe 30 to a mixer 300.
  • Hydrogen peroxide solution is added to the mixer 300 through pipe 35 in a quantity sufficient to assure desired brightness development will be achieved at the end of the reaction.
  • magnesium compounds for protection of cellulose viscosity may also be added with the alkali solution through pipe 15, the peroxide solution through pipe 35, or separately through pipe(s) 16 and/or 36.
  • sequestrants such as SiO 2
  • chelants such as EDTA or DTPA
  • the pulp which has been heated to the desired reaction temperature, and adjusted to the desired pH, is pumped through pipe 40 into the upflow tube column 400, which is sized for the retention time desired for the reaction.
  • the upflow tube is sized to assure a pulp retention time of 1-30 minutes, preferably 5-20 minutes, after which the pulp is discharged through pipe 50 to an appropriate discharge device 500, such as a valve, and thence through pipe 60 to subsequent washing and bleaching stages.
  • an appropriate discharge device 500 such as a valve
  • water or liquor at a cooler temperature may be used for dilution into the top of the upflow tube through pipe 70.
  • Fig. 2 schematically describes another preferred embodiment of the present invention which is identical to that shown in Fig. 1, except for the addition of a downflow tower 600.
  • the upflow tube is sized to assure a pulp retention time of 1-30 minutes, preferably 5-20 minutes, after which the pulp is discharged through pipe 50 to an appropriate discharge device 500, such as a valve, through pipe 60 to a conventional bleaching tower 600, preferably one which is already installed at the pulp mill and can be reused for this new bleaching stage instead of a chlorine based bleaching sequence.
  • the pulp is retained in this tower for an additional 1-5 hours at the desired reaction temperature to consume a substantial portion of the hydrogen peroxide applied on the pulp.
  • the pulp is bleached in column 400 at more than 100°C., it may be desirable to reduce this temperature to prevent "flashing" of the pulp.
  • This embodiment may be desirable in some mills to limit potential emissions of steam and residual chemical to the atmosphere. This may be accomplished by adding cooler water or liquor to dilute the pulp through pipe 70. For example, for pulp treated in the upflow column at 12% consistency at 110°C., the addition of 1.5-2.5 m 3 /ton pulp of 50-60°C. liquor, will cool the pulp to less than 100°C., and result in a drop in consistency to about 10% consistency, which will not significantly decrease the performance of the second step of the reaction. It may be especially desirable to maintain the pulp at the maximum temperature allowable at atmospheric pressure.
  • the pulp is discharged from pipe 60 into tower 600 and is allowed to flash to atmospheric pressure.
  • the pulp entering the downflow tower will be at its maximum possible temperature, for example, 98-100°C., which will enhance the consumption of peroxide in the second phase of the reaction.
  • the flashed steam discharges through pipe 90 to heat exchanger 700.
  • the heat exchanger is used to pre-heat the wash water applied on the washer prior to the peroxide stage, thereby reducing the amount of steam necessary to be applied to the stage through pipes 15 and 37. This increases the temperature of the wash water in pipe 101 prior to its application to the conventional washer through pipe 110.
  • Fig. 3 The embodiment shown in Fig. 3 is identical to that of Fig. 2 up to the point of discharge of the pulp from upflow reaction column 400. In this case the pulp retains a substantial amount of residual peroxide upon discharge.
  • the pulp is discharged through pipe 50 to an appropriate mixing valve 500, where additional alkali is added through pipe 55 to increase the pH of the pulp to more than 8.5, preferably 9.5-10.5 for the second step of the reaction.
  • the pulp after flash cooling, is discharged through pipe 60 to a conventional downflow tower 600, for the second phase of the reaction.
  • the conventional downflow tower is sized to consume a substantial portion of the remaining peroxide, and will typically retain the pulp for 1-5 hours. Bleached pulp is discharged from tower 600 through pipe 80 to subsequent process steps.
  • the valve 500 serves to reduce the pressure from the upflow tube 400 and allow the liquor with the pulp to flash.
  • the alkali is added to the pulp just upstream of the valve, and the turbulence created in the valve serves to mix the alkali with the pulp. It is recognized that the installation of any mixing device at this location of the process is substantially equivalent to the function of the valve.
  • Fig. 4 describes another preferred embodiment of the present invention which is identical to Fig. 3, except for reactivation of pulp in mixing device 550.
  • the upflow tube is sized to assure a pulp retention time of 1-30 minutes, preferably 5-20 minutes, after which the pulp is discharged through pipe 50 to an appropriate mixing device 550, in which the residual peroxide is reactivated by the addition of alkali through pipe 55, after which the pulp is allowed to flash and steam from such flashing is conducted through pipe 90 to heat exchanger 700 to preheat the water from pipe 101 to higher temperature water which is discharged through pipe 110 and used for washing of the pulp upstream of the bleaching stage.
  • Fig. 5 is a schematic diagram of a bleaching sequence employing the present invention.
  • Pulp from a washer or thickener 10 is discharged through pipe 11 and is fed to a mixer 20, where steam and/or bleaching chemicals are applied through pipe(s) 12 and 13 to heat the pulp to the desired reaction temperature, and to increase the pH of the pulp to the desired level for first treatment with peroxide.
  • the heated and pH adjusted pulp is discharged through pipe 21 to a pump 30 to transfer the pulp to a mixer 40.
  • the pulp will be heated to above 100°C., it is conventional to apply steam for final heating ahead of the mixer, typically through a pipe 34.
  • Additional chemicals including alkali, peroxide, chelants, and others may be added through pipes 32 and 33, and homogeneously mixed with the pulp prior to discharge through pipe 41 to the first peroxide reaction vessel 50.
  • the peroxide reaction vessel 50 is sized for 1-30 minutes retention time, preferably 5-20 minutes to achieve substantial delignification and/or brightness increase prior to being discharged through pipe 51 to a discharge device 52. It is preferable for the best operating cost of the sequence, but not necessary, to wash the pulp following the first peroxide treatment, and if the washing device is a non pressurized device, it will be preferable to cool the pulp prior to discharge from the first peroxide reaction vessel. Cooler dilution liquor may be added in the first peroxide reaction vessel 50 through pipe 53. It may be desirable to dilute the pulp prior to the pump with filtrate fed through pipe 54 if the washing device requires low consistency pulp for its proper operation.
  • the pulp is washed on washer 60, and the washed pulp is discharged through pipe 61 to a mixer 70.
  • the second step in this preferred embodiment is an ozone stage which may be operated at either high or medium consistency, however, it is preferable that this be a medium consistency stage operating at conventional washer discharge consistencies of 10-14% to minimize the capital cost for the installation. As is known in the prior art, it is necessary to operate at a pH of less than 4 to achieve optimum results from the ozone stage.
  • an acid such as sulfuric acid
  • an acid such as sulfuric acid
  • the acidified pulp is pumped with pump 70 through pipe 71 to a mixer 80, in which ozone gas is applied through pipe 72 .
  • the pulp is discharged to the ozone reaction vessel 90 and is held for up to about 10 minutes to allow nearly complete consumption of the ozone.
  • the pulp is discharged from he ozone reaction vessel through pipe 91 to a discharge device 92, which may consist of a valve, a plurality of valves, or a mechanical device to reduce the pressure from the ozone reaction vessel.
  • the pulp is discharged through pipe 93 to a gas separation device 220, where the gas is separated from the pulp and is discharged through pipe 202 to treatment and/or reuse in the mill.
  • the degassed pulp is discharged through pipe 102 to a pump 210. It is preferable for the best operating cost of the sequence, but not necessary, to wash the pulp following the ozone stage prior to the next stage of bleaching. It may be desirable to dilute the pulp prior to the pump with filtrate fed through pipe 103 if the washing device requires low consistency pulp for its proper operation.
  • the pulp is fed through pipe 104 to washer 120, and is washed using water or filtrate applied through pipe 115.
  • Pulp from the washer 120 is discharged through pipe 121 and is fed to a mixer 130, where steam and/or bleaching chemicals are applied through pipe(s) 122, 123, and 124 to heat the pulp to the desired reaction temperature, and to increase the pH of the pulp to the desired level for first treatment with peroxide.
  • the heated and pH adjusted pulp is discharged through pipe 131 to a pulp 140 to transfer the pulp through pipe 141 to a mixer 150.
  • As the pulp will be heated to about 100°C., it is conventional to apply steam for final heating ahead of the mixer, typically through a pipe 144.
  • Additional chemicals including alkali, peroxide, chelants, and others may be added through pipes 142 and 143, and homogeneously mixed with the pulp prior to discharge through pipe 151 to the second peroxide reaction vessel 160.
  • the peroxide retention vessel 160 is again sized for 1-30 minutes retention time, preferably 5-20 minutes to achieve substantial delignification and/or brightness increase prior to being discharged through pipe 161 to a discharge device 152. It is preferable to wash the pulp following the second peroxide treatment; however, it may not be necessary if an additional bleaching stage is added which is not significantly affected by the presence of residual peroxide and/or dissolved organic matter.
  • the washing device is a non pressurized device, it will be preferable to cool the pulp prior to discharge from the first peroxide reaction vessel. Dilution of the pulp with a cool liquor may be accomplished in the second peroxide reaction vessel 160 through pipe 153. It may be desirable to dilute the pulp prior to the pump with filtrate fed through pipe 154 if the washing device requires low consistency pulp for its proper operation. The pulp is then washed on a washing device 180 using water or filtrate applied through pipe 156.
  • Fig. 6 is a schematic diagram of a bleaching sequence employing the present invention applied to an existing bleach plant.
  • a typical sequence which exists in many bleach plants today is DcEoDED.
  • An existing conventional bleach plant may be modified to incorporate the concepts according to the present invention very economically.
  • the investment for conversion may be as little as three mixers, three reaction vessels, an ozone generator, and miscellaneous piping to incorporate the change. In some cases, it may be necessary to make some changes to the materials in existing bleach towels, piping, and other equipment.
  • the existing chlorination tower may not be used in the new bleaching sequence, but may serve as additional storage or other pretreatment prior to the new bleach plant.
  • the existing Eo stage will be used as a chelant stage where EDTA, DTPA, or other chelant is added and is operated at a controlled pH and temperature, preferably 5-7 pH and 10-60°C.
  • the retention time of 30-90 minutes that typically exists in a conventional Eo stage is suitable for the chelation stage.
  • the existing D1 stage After washing on the existing Eo washer, the existing D1 stage will be used as a first peroxide stage (P1), by diverting the pulp to a new mixer suitable for addition of peroxide, adding the appropriate reaction vessel, and discharging to the existing D1 tower, with or without reactivation of residual peroxide according to the present invention.
  • the first peroxide stage will operate at a pH of about 8.5 to about 12.5, with the first step of the reaction at a temperature of greater than 100°C., preferably 105-120°C., with a reaction time of 1-30 minutes, preferably 5-20 minutes.
  • the existing E stage After washing on the existing D1 washer, the existing E stage will be used as an ozone stage, by diverting the pulp to a new mixer suitable for addition of ozone, adding the appropriate reaction vessel and gas separator, and discharging to the existing E tower.
  • the ozone stage will operate at a pH of less than 4, preferably 2-4, at a temperature of 30-70°C., preferably less than 50°C., with a reaction time of less than 10 minutes preferably less than 5 minutes.
  • the existing D2 stage After washing on the existing D2 washer, the existing D2 stage will be used as a second peroxide stage (P2), by diverting the pulp to a new mixer suitable for addition of peroxide, adding the appropriate reaction vessel, and discharging to the existing D2 tower, with or without reactivation of residual peroxide according to the present invention.
  • the second peroxide stage will operate at a pH of about 8.5 to about 12.5, with the first step of the reaction at a temperature of greater than 100°C., preferably 105-120°C., with a reaction time of 1-30 minutes, preferably 5-20 minutes.
  • the pulp may proceed to subsequent post treatments, but preferably will be fully bleached pulp to be transferred to the bleached high density storage tower.
  • Figure 7 illustrates a preferred method for the reuse of filtrates in the QPZP sequence. It is noted that according to the present invention, there is substantial residual peroxide with the pulp following the peroxide treatment, for example, normally the peroxide charged is 2.5% on pulp, but the amount of peroxide consumed in the reaction is typically less than 1.5% on pulp. As peroxide is a relatively expensive bleaching chemical, it is desirable to recover this residual for reuse in the peroxide stages. This is accomplished by recirculating filtrate from the post peroxide stage washing to the washing step preceding the peroxide stage as shown in the Figure. For illustration, typical filtrate flows are shown in the Figure, for example, with each washer discharging at 10% consistency, the filtrate flow with the pulp is 9 kg liquor/kg pulp.
  • the filtrate is recirculated countercurrently through the bleach plant such that the residual peroxide is applied to the pulp on the washer, and a substantial portion of this residual peroxide then carries forward to the peroxide stage.
  • the required peroxide application in the stage is then reduced by the amount carried forward with the pulp.
  • the amount of peroxide residual carried forward is a function of the displacement ratio (washing efficiency) of the washer. For example, if the washer has a displacement ratio of 0.85, then about 60% of the peroxide residual will be recovered.
  • the bleach chemical used in the sequence is reduced substantially by recirculation of filtrates as shown in Figure 7, compared to other filtrate recycle schemes which may be considered.
  • Figure 8 illustrates another preferred method for the reuse of filtrates in the QPZP sequence, which may be preferred if the bleach plant is to be constructed new, that is, without reuse of existing equipment in a bleach plant.
  • Figure 8 includes the use of presses, preferably Twin Roll Washing Presses manufactured by Ingersoll-Rand Company, instead of conventional vacuum or pressure washers or vacuum or pressure diffusers. Typical filtrate flows are shown in the Figure, with each press discharging at 33.3% consistency, the filtrate flow with the pulp is 2 kg liquor/kg pulp.
  • the wash water flow to each washer, at a dilution factor of 2, which is typical in bleach plants today, is 4 kg liquor/kg pulp. In this case, the filtrate is used for washing on the press similar to the concept described in Figure 7.
  • the filtrate which contains substantial residual peroxide is also used for dilution of the pulp discharged from the press in the amount of 7 kg liquor/kg pulp.
  • the amount of peroxide recovered is similar to that with the vacuum washer case described in Figure 7.
  • the amount of filtrate recovered in the press is a function of the displacement ratio (washing efficiency) of the press. If the press has a displacement ratio of 0.40, a total recovery of about 60% of the peroxide residual is achieved. This may be attractive for new construction as presses have similar capital requirements as conventional vacuum or pressure washers.
  • One additional benefit of this configuration is the ability to incorporate high consistency ozone bleaching rather than medium consistency ozone bleaching if the washing devices installed are presses. This option reduces the amount of ozone required for bleaching, and reduces the energy demand in the bleach plant.
  • pulp from a conventional washer or thickener is discharged through pipe 10 into mixer 100, where steam for heating the pulp and/or alkali is used for increasing the pH of the pulp is added through pipe 15.
  • the pulp is heated and adjusted to a pH of about 11.
  • the heated and pH adjusted pulp is discharged from mixer 100 through pipe 20 to a conventional medium consistency pump 200 which pumps the pulp through pipe 30 to a mixer 300.
  • Hydrogen peroxide solution is added to the mixer 300 through pipe 35 in a quantity sufficient to assure substantial residual will be maintained at the end of the first step of the reaction.
  • magnesium compounds for protection of cellulose viscosity may also be added with the alkali solution through pipe 15.
  • sequestrants such as silicate and/or chelants ⁇ such as EDTA or DTPA ⁇
  • the peroxide solution can be applied through pipe 35, or separately through pipe(s) 16 and/or 36.
  • the final temperature rise from, for example, 85-90°C. to in excess of 100°C. is achieved by adding steam between the pump 200 and the mixer 300 through pipe 37.
  • the pulp which has been heated to the desired reaction temperature, and adjusted to the desired pH, is pumped through pipe 40 into the upflow tube 400, which is sized for the retention time desired for the first phase of the reaction.
  • the upflow tube is sized to assure a pulp retention time of 5-30 minutes, preferably 5-20 minutes, after which retention time, the pulp retains a substantial residual of peroxide in the pulp slurry.
  • the pulp is discharged through pipe 50 to an appropriate pressing device 560, where the consistency of the pulp is raised from about 10% to about 25%.
  • the filtrate is recycled through pipe 55 to pipe 30 to recover a portion of the peroxide not consumed in the first step of the reaction.
  • the pulp is discharged through pipe 60 to a conventional downflow tower 600, for the second step of the reaction which is operated at high consistency (25-30%).
  • the conventional downflow tower is sized to consume a substantial portion of the remaining peroxide, and will typically retain the pulp for 1-5 hours. Bleached pulp is discharged from tower 600 through pipe 80 to subsequent process steps.
  • the first step of the PAPEROXIDE process is to react the pulp with peroxide at a pH of 8.5-12.5 and at high temperature (>100°C.) for a limited time of less than about 30 minutes, preferably 5-20 minutes. It is important that this step be performed without causing metal contamination of the pulp slurry.
  • the result of this first step is illustrated in the example below:
  • pulp sample was then treated in a chelation stage using 0.6% EDTA on pulp at about 50°C. and for 30 minutes retention time.
  • This pulp sample was then further delignified using a conventional hydrogen peroxide stage and an ozone stage to achieve a kappa number of 1.3 with a brightness of 81.8% ISO.
  • the fundamental principle of this invention is to gain rapid delignification and brightness development in a relatively short period of time, at temperatures of about 100-120°C. and retention time in a small reaction column of less than about 30 minutes, and then discharging the pulp into a conventional large retention tower for about 1-5 hours at atmospheric pressure, i.e., less than about 100°C., without washing the pulp in between the two steps.
  • the use of subsequent retention time at atmospheric pressure for conventional retention times of 1-5 hours will lead to further consumption of hydrogen peroxide accompanied by a further brightness increase. This may allow the incoming pulp to be received at lower brightness than the pulp in the example.
  • This peroxide stage design can be further improved by combining the principle of high temperature and short retention time with reactivation of residual peroxide followed by conventional bleach tower retention.
  • the peroxide solution is added in more than sufficient quantities to guarantee a significant peroxide residual after the completion of the first step of the reaction, which is conducted for a retention time of 1-30 minutes, but preferably for 5-20 minutes, assuring therefore a peroxide residual entering the second step of the reaction.
  • This invention can be applied to the rebuild of existing bleach plants and/or the construction of new bleach plants for the production of ECF or TCF pulps.
  • the use of a short, high temperature peroxide step with or without subsequent retention and with or without reactivation of residual peroxide, and in combination with conventional bleaching chemicals allows very economical construction of short retention time bleach plants.
  • TCF pulp at high brightness, for example, greater than 80%ISO, from an oxygen delignified softwood kraft pulp with an entering kappa number of about 14.
  • This bleaching concept allows the full bleaching operation to take place with a total retention time in the bleach plant of less than two hours. Due to the small bleaching reactors compared to conventional bleaching technology, this approach has an unprecedented low capital cost compared to all current approaches to production of TCF pulps. This is illustrated in the following example:
  • This pulp sample was then treated in a chelation stage using 0.6%EDTA on pulp at about 50°C. and for 30 minutes retention time, followed by bleaching of the pulp to greater than 85% ISO brightness in a P-Z-P sequence.
  • the peroxide stages were performed using short (5-15 minutes), high temperature (107-110°C.) conditions, but with the addition of a conventional ozone bleaching step between the two peroxide stages.
  • the brightness of the bleached pulp is 82.3, 87.6, and 91.0 for total retention times in the two peroxide stages of 10, 20, and 25 minutes, respectively. It should be noted that the kappa number of the bleached pulp is quite low, for example, less than 3.
  • pulp mills today which practice TCF bleaching of pulp using only peroxide as the active bleaching chemical, and these mills produce fully bleached pulps at an exceedingly high kappa, for example, greater than 5, which is undesirable especially from the view of brightness reversion in the paper produced from such pulps.
  • This combination of the use of the first step of the present invention with established ozone bleaching technology has a substantial advantage over current commercial practice for paper quality made from the pulps produced through use of this process.
  • the simulation of this sequence includes an ozone stage operating at high consistency for convenience in the laboratory simulation, that is, about 40% consistency; however, it is recognized that for moderate doses of ozone on pulp, that is, less than about 0.6%, essentially the same results will be achieved when using medium consistency ozone, that is, about 10-14% consistency.
  • the present invention is therefore not intended to be limited to the use of high consistency ozone, in fact, it is preferable to use medium consistency ozone in order to utilize existing equipment in the mill, and this is thus described in the preferred embodiment.
  • the modification of an existing bleach plant using, for example, the existing extraction, hypochlorite, or chlorine dioxide bleaching towers as subsequent retention following the short, high temperature step of the peroxide bleaching stage according to the present invention reduces the operating cost of the bleaching sequence compared to the previous example, and requires minimum added equipment to the existing bleaching plant.
  • This pulp sample was then treated in a chelation stage using 0.6% EDTA on pulp at about 50°C. and for 30 minutes retention time, followed by bleaching of the pulp to greater than 85% ISO brightness in a P1-Z-P2 sequence.
  • the peroxide stages were performed using short (5-15 minutes), high temperature (107-110°C.) conditions, but with the addition of atmospheric retention time following each of the short, high temperature, peroxide stages, and in combination with a conventional ozone bleaching step between the two peroxide stages.
  • the investment per peroxide bleaching stage is reduced to about $250,000 or less, or a total investment for the 350 mills in North American industry of about $90 million. Compared to the prior art, this represents a savings of between $130-430 million.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
  • Detergent Compositions (AREA)
EP98204179A 1994-07-11 1995-06-29 Procédé de blanchiment au péroxyde de substances cellulosiques et lignocellulosiquesm Withdrawn EP0919661A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US27353994A 1994-07-11 1994-07-11
US273539 1994-07-11
EP95926123A EP0797703B1 (fr) 1994-07-11 1995-06-29 Procede de blanchiment au peroxyde de substances cellulosiques et lignocellulosiques

Related Parent Applications (1)

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EP95926123A Division EP0797703B1 (fr) 1994-07-11 1995-06-29 Procede de blanchiment au peroxyde de substances cellulosiques et lignocellulosiques

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EP0919661A1 true EP0919661A1 (fr) 1999-06-02

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EP98204179A Withdrawn EP0919661A1 (fr) 1994-07-11 1995-06-29 Procédé de blanchiment au péroxyde de substances cellulosiques et lignocellulosiquesm
EP95926123A Revoked EP0797703B1 (fr) 1994-07-11 1995-06-29 Procede de blanchiment au peroxyde de substances cellulosiques et lignocellulosiques

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EP (2) EP0919661A1 (fr)
JP (1) JP2787618B2 (fr)
CN (1) CN1176673A (fr)
AT (1) ATE189716T1 (fr)
BR (1) BR9508388A (fr)
CA (1) CA2194880A1 (fr)
DE (2) DE69515066T2 (fr)
ES (1) ES2107399T3 (fr)
FI (1) FI970104A (fr)
PT (1) PT797703E (fr)
RU (1) RU2141016C1 (fr)
WO (1) WO1996001920A1 (fr)
ZA (1) ZA955290B (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7297225B2 (en) * 2004-06-22 2007-11-20 Georgia-Pacific Consumer Products Lp Process for high temperature peroxide bleaching of pulp with cool discharge

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU5823896A (en) * 1995-06-20 1997-01-22 A. Ahlstrom Corporation Method and apparatus for treating material which conducts heat poorly
JP2002266272A (ja) * 2001-03-12 2002-09-18 Nippon Paper Industries Co Ltd セルロース質繊維材料パルプの漂白方法
US20050051288A1 (en) * 2003-09-09 2005-03-10 Caifang Yin Extended retention and medium consistency pulp treatment
CN100412267C (zh) * 2006-04-30 2008-08-20 华南理工大学 一种中浓纸浆过氧化氢双塔漂白方法
FR2910027B1 (fr) * 2006-12-13 2009-11-06 Itt Mfg Enterprises Inc Procede de blanchiment des pates papeteries chimiques par traitement final a l'ozone a haute temperature
JP5585323B2 (ja) * 2010-09-07 2014-09-10 王子ホールディングス株式会社 製紙用パルプの漂白方法
CN115821617B (zh) * 2022-12-06 2024-01-05 金隆浆纸业(江苏)有限公司 一种纸浆漂白方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0285530A1 (fr) * 1987-04-02 1988-10-05 Elf Atochem S.A. Procédé de blanchiment de pâtes
FR2661430A1 (fr) * 1990-04-30 1991-10-31 Atochem Procede de blanchiment au peroxyde d'hydrogene de pates a papier a haut rendement.
EP0578304A1 (fr) * 1992-07-06 1994-01-12 SOLVAY INTEROX (Société Anonyme) Procédé pour le blanchiment d'une pâte à papier chimique

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE500616C2 (sv) * 1993-06-08 1994-07-25 Kvaerner Pulping Tech Blekning av kemisk massa med peroxid vid övertryck

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0285530A1 (fr) * 1987-04-02 1988-10-05 Elf Atochem S.A. Procédé de blanchiment de pâtes
FR2661430A1 (fr) * 1990-04-30 1991-10-31 Atochem Procede de blanchiment au peroxyde d'hydrogene de pates a papier a haut rendement.
EP0578304A1 (fr) * 1992-07-06 1994-01-12 SOLVAY INTEROX (Société Anonyme) Procédé pour le blanchiment d'une pâte à papier chimique

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7297225B2 (en) * 2004-06-22 2007-11-20 Georgia-Pacific Consumer Products Lp Process for high temperature peroxide bleaching of pulp with cool discharge

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Publication number Publication date
CA2194880A1 (fr) 1996-01-25
PT797703E (pt) 2000-07-31
FI970104A (fi) 1997-03-10
ZA955290B (en) 1996-12-27
ATE189716T1 (de) 2000-02-15
RU2141016C1 (ru) 1999-11-10
JP2787618B2 (ja) 1998-08-20
ES2107399T1 (es) 1997-12-01
DE69515066T2 (de) 2001-04-19
BR9508388A (pt) 1998-07-14
EP0797703A1 (fr) 1997-10-01
FI970104A0 (fi) 1997-01-10
EP0797703B1 (fr) 2000-02-09
JPH09508945A (ja) 1997-09-09
ES2107399T3 (es) 2000-07-01
CN1176673A (zh) 1998-03-18
DE797703T1 (de) 1998-02-19
WO1996001920A1 (fr) 1996-01-25
DE69515066D1 (de) 2000-03-16

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