EP0565625A1 - Procede de blanchiment de pate lignocellulosique sans utilisation de chlore - Google Patents

Procede de blanchiment de pate lignocellulosique sans utilisation de chlore

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Publication number
EP0565625A1
EP0565625A1 EP19920904154 EP92904154A EP0565625A1 EP 0565625 A1 EP0565625 A1 EP 0565625A1 EP 19920904154 EP19920904154 EP 19920904154 EP 92904154 A EP92904154 A EP 92904154A EP 0565625 A1 EP0565625 A1 EP 0565625A1
Authority
EP
European Patent Office
Prior art keywords
pulp
brightness
peroxide
consistency
bleaching
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP19920904154
Other languages
German (de)
English (en)
Inventor
Omar F. Ali
Bruce F. Griggs
Thomas P. Gandek
Michael A. Pikulin
Allen Rosen
Stuart T. Territ
Spencer W. Eachus
David E. White
William H. Friend
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.)
Union Camp Patent Holding Inc
Original Assignee
Union Camp Patent Holding Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Union Camp Patent Holding Inc filed Critical Union Camp Patent Holding Inc
Publication of EP0565625A1 publication Critical patent/EP0565625A1/fr
Ceased legal-status Critical Current

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
    • 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

Definitions

  • the invention relates to methods of bleaching lignocellulosic materials and more particularly, to a multi-stage, chlorine-free process for bleaching wood pulp.
  • the pulp is subjected to an alkaline extraction to remove a substantial portion of any remaining lignin and to prevent redeposition upon the pulp of the by-products from the previous reactions.
  • This treatment is then followed by a final bleaching treatment with an alkaline peroxide solution.
  • OZP oxygen, ozone, peroxide
  • the process of the present invention provides novel combinations of delignification and bleaching steps which eliminate the problems encountered in the prior art by increasing the efficiency and reducing the cost and duration of pulp bleaching.
  • the multi-stage process of the invention also eliminates the use of elemental chlorine and/or chlorine-containing bleaching agents, thus substantially reducing or eliminating pollution of the environment while optimizing the physical properties of the resultant pulp product in an energy efficient, cost effective manner.
  • the present process can work on virtually all wood species, including the difficult-to- bleach southern U.S. softwoods, as well as the more readily bleached hardwoods.
  • Applicants 1 process includes several stages, i.e., a pulping stage, an oxygen delignification stage and an ozone delignification/bleaching stage which together comprise what will be referred to herein as the "front end" of the process.
  • the process further comprises a hydrogen peroxide bleaching stage, which follows directly upon completion of the ozone treatment.
  • the peroxide bleaching stage is referred to in the present specification as the "back end" of the process.
  • the present process does not require or utilize an extraction stage between the ozone delignification/ bleaching treatment and the peroxide bleaching stage, thus reducing both its cost and duration in contrast to prior art bleaching processes, while obtaining pulp with GE brightness values comparable to those in the prior art without sacrificing pulp strength.
  • the present process reduces the amount of lignin as much as is practical in the front end of the process (as evidenced by a corresponding decrease in the K No. of the pulp) without a concomitant substantial (and therefore unacceptable) decrease in pulp strength.
  • This ensures that the viscosity of the pulp exiting the ozone delignification bleaching stage remains sufficiently high to permit the pulp to withstand the effects of the subsequent peroxide bleaching treatment, thus enabling the formation of a final bleached pulp product having sufficient strength and GE brightness (“GEB”) for its intended application.
  • GEB GE brightness
  • the substantially delignified pulp preferably has a GEB of from about 59-65.
  • the subsequent hydrogen peroxide bleaching treatment raises the GE brightness value to about 75 or, in an alternate embodiment, to at least about 83-86.
  • the peroxide treatment phase of the invention may be carried out along a number of paths as described below, with the option chosen depending, at least in part, upon the final GE brightness which is desired for the finished pulp.
  • Fig. 1 schematically illustrates the pulping, oxygen delignification and ozone delignification/bleaching steps which comprise the front end of the process of the invention
  • Fig. 2 schematically illustrates the peroxide bleaching stage at the back end of applicants' process
  • Fig. 3 is a plot of ozone GEB vs. peroxide ceiling GEB obtained with a Kraft-AQ/O m /Z m /P pulp. petailed Description of the Preferred Embodiments
  • the first stage in the method of the present invention is the pulping step.
  • procedures may be utilized which improve the amount of lignin removed from the lignocellulosic material, while minimizing the amount of degradation of the cellulose.
  • FIG. 1 A processing scheme for carrying out the "front end" of the method of the present invention is illustrated in schematic form in Fig. 1.
  • Wood chips 2 are introduced into a digester 4 together with a white liquor 6 comprising sodium hydroxide, sodium sulfide and, in the preferred embodiment, an anthraquinone additive.
  • a white liquor 6 comprising sodium hydroxide, sodium sulfide and, in the preferred embodiment, an anthraquinone additive.
  • Sufficient white liquor should be introduced into digester 4 to substantially cover the wood chips.
  • the contents of digester 4 are then heated at a temperature and for a time sufficient to allow the liquor to substantially impregnate the wood chips.
  • the use of the Kraft/AQ pulping technique is preferred since the inclusion of the anthraquinone additive contributes significantly to the degree of lignin removal without causing significant adverse affects upon the desired strength characteristics of the remaining cellulose.
  • the amount of anthraquinone in the cooking liquor should be at least about 0.01% by weight, based upon the oven dried ("OD") weight of the wood to be pulped, with amounts of from about 0.02 to 0.1% generally being preferred.
  • OD oven dried
  • the Kraft/AQ technique costs more to perform than, for example, an unmodified Kraft treatment, this additional cost is at least partially offset by the savings in the cost of chemicals needed for the subsequent oxygen, ozone and peroxide stages.
  • the pulping stage can be carried out with the use of techniques for extended delignification such as the Ka yr MCC, Beloit RDH and Sunds Cold Blow methods. These techniques also offer the ability to remove more of the lignin during cooking without adversely affecting the desired strength characteristics of the remaining cellulose to a significant degree. Still further, the pulping stage may be carried out, if desired, with the use of an unmodified Kraft process. The brownstock pulp which results from the use of this technique is darker in color than that obtained with the Kraft/AQ and extended delignification processes described above due to the presence of a greater amount of unbleached lignin remaining in the pulp.
  • techniques for extended delignification such as the Ka yr MCC, Beloit RDH and Sunds Cold Blow methods. These techniques also offer the ability to remove more of the lignin during cooking without adversely affecting the desired strength characteristics of the remaining cellulose to a significant degree.
  • the pulping stage may be carried out, if desired, with the use of an un
  • the Kraft process is therefore not particularly practical for use in the present invention unless it is coupled with an oxygen treatment which is sufficient to remove correspondingly more lignin in the oxygen delignification step without adversely affecting the strength of the oxygen delignified pulp.
  • This combination is capable of producing a pulp of sufficient brightness and viscosity to permit effective ozone and peroxide bleaching to the high GEB values stated above.
  • the combination of Kraft pulping plus "standard" oxygen delignification (described below) produces a pulp which does not retain sufficient viscosity, i.e., strength, to form a useful product upon completion of the remainder of applicants' process as described herein.
  • the pulping step is conducted so that, for a southern U.S. softwood, for example, a K No. in the range of about 16-20, a cupriethylenediamine ("CED") viscosity in the range of about 18-28, and a GE brightness in the range 15-25 is typically obtained.
  • CED cupriethylenediamine
  • the digester 4 produces a black liquor containing the reaction products of lignin solubilization together with the brownstock pulp 8.
  • the cooking step is typically followed by washing to remove most of the dissolved organics and cooking chemicals for recycle and recovery, as well as a screening stage (not shown) in which the pulp is passed through a screening apparatus to remove bundles of fibers that have not been separated in pulping.
  • the brownstock 8 is treated in 5 washing units comprising, in sequence, a blow tank 10 and washing unit 12 where residual liquor 14 contained in the pulp is removed.
  • Oxygen Delignification 10 The next stage in the process of the present invention, i.e., the oxygen delignification step, primarily involves removal of residual lignin from the brownstock pulp. In one oxygen delignification technique (i.e., "0") well-known in the prior art, the washed pulp
  • the oxygen deligni ⁇ fication treatment may be modified and conducted in a manner which allows for the removal of increased __. percentages of the lignin remaining in the brownstock pulp without causing an unacceptable corresponding decrease in the viscosity of the pulp.
  • This allows conventional Kraft pulping to be used with such modified oxygen delignification techniques while still obtaining the desired K Nos. and viscosities.
  • the brownstock pulp is treated at low to medium consistency with an amount of alkali necessary to ensure uniform application thereof upon the pulp.
  • the brownstock is maintained at a pulp consistency of less than about 10% and preferably less than about 5% by weight.
  • the consistency of the pulp is generally greater than about 0.5%, however, since lesser consistencies are not economical to process in this manner.
  • a most preferred consistency range is 0.5 to 4.5%.
  • the consistency of the pulp is raised to at least 18 percent.
  • the pulp consistency is raised from about 20-25% to about 35%, and even more preferably, to about 27%.
  • the high consistency pulp is directed to an oxygen reactor for delignification using conventional conditions.
  • the advantage of using the O m process is illustrated by comparison of the K Nos. and viscosities obtained using southern softwoods to those obtained with the O process under otherwise substantially identical process conditions.
  • the pulp thus obtained will typically have a K No. of about 12 to 14 and a viscosity of about 15. This K No. is too large to permit later delignification using the ozone stage of the present invention.
  • the use of conventional Kraft pulping with the modified high consistency oxygen bleaching surprisingly results in a pulp having a K No. of less than about 9, while the viscosity of the pulp is maintained above about 12 to 14.
  • K No. and viscosity are related in that the ratio of the change in viscosity to the change in K No. , referred to as the "delignification selectivity" of the process, is a measure of the efficiency of the O m technique for removing lignin while maintaining adequate levels of viscosity therein.
  • the use of the 0 m process, as described above, thus results in an enhanced degree in the selectivity of the delignification, signified by a reduction in K No. of at least about 20% greater than that obtained with the use of an "O" stage.
  • the combination of Kraft pulping and 0 m oxygen delignification will result in an enhanced delignification selectivity, i.e., a sufficiently low K No. and a sufficiently high viscosity, to permit further delignification and bleaching by ozone and peroxide.
  • a first amount of alkaline material is applied to pulp at low consistency by combining the pulp with a quantity of alkaline material in an aqueous alkaline solution.
  • the consistency of the pulp is then increased to a high consistency of at least about 18%.
  • a second amount of alkaline material is applied to the high consistency pulp to obtain a total amount of alkaline material applied to the pulp.
  • the pulp is then subjected to oxygen delignification whereby the enhanced delignification selectivities of the 0 m process are achieved.
  • the alternate 0 S technique is most preferred because a lower proportion of the alkaline material (i.e., than with the 0 m process) is applied to the low consistency pulp. This, in turn, reduces the amount of alkaline material utilized in mixing chest 18 and also reduces the amount of this material removed via pressate discharge 32 (see below) .
  • pressate discharge 32 see below
  • splitting the application of the alkaline material between the high and low consistency pulp reduces the amount of pressate discharge 32 which, in turn, reduces the amount of alkaline material which must be reintroduced, thus saving chemical. Further the high consistency alkaline treatment portion of the 0.
  • the method permits rapid modification of the amount of the alkaline material present in the pulp entering the oxygen delignification reactor to compensate for changes in the properties (i.e., wood type. Kappa or K. No. and viscosity) of the incoming brownstock, or to vary the degree or extent of oxygen delignification for a particular pulp.
  • washed brownstock 16 is introduced into a mixing chest 18 where it is substantially uniformly treated with sufficient alkaline material 20 for a time sufficient to distribute a first amount of alkaline material throughout the pulp.
  • the low consistency treatment portion of this 0, process is carried out in the same manner as the 0 m process, but less alkaline material (i.e., about half as much) is applied to the pulp.
  • an aqueous sodium hydroxide solution is combined with the low consistency pulp in an amount sufficient to provide essentially the same amounts on the OD pulp as was achieved by the O process.
  • At least about 0.4% to about 3.5% by weight of sodium hydroxide is deposited on the pulp, based on oven dry pulp after thickening with the balance applied to the high consistency pulp.
  • Other alkali sources having equivalent sodium hydroxide content can also be employed instead of sodium hydroxide if desired.
  • Oxidized white liquor is a convenient plant stream which may be utilized.
  • the alkaline treated pulp 22 is forwarded to a thickening unit 24 such as a twin roll press where the consistency of the pulp is increased to the desired value.
  • the pulp consistency increasing step also removes residual liquid or pressate 26. A portion 28 of this pressate 26, ay be directly recycled back to brownstock washer 12.
  • a portion 30 may instead be directed to mixing chest 18 for use in the low consistency pulp alkaline treatment step. Since the consistency of the pulp is increased in the thickening unit 24, a certain amount 32 of pressate may continually be discharged to the plant liquid recovery system to maintain water balance in the mixing chest 18.
  • Additional alkaline material 36 is applied to the high consistency brownstock 34 produced by the thickening unit 24 to obtain the desired total amount of alkaline material on the pulp prior to oxygen delignification.
  • This total amount of alkaline material is selected to achieve the desired extent of delignification in the subsequent oxygen delignification step which is carried out on the alkaline material treated high consistency pulp.
  • the total amount of alkaline material actually applied onto the pulp will generally be between 0.8 and 7% by weight based on oven dry (“OD") pulp, and preferably between about 1.5 and 4% for southern softwood and between about 1 and 3.8% for hardwood. About half these amounts are preferably applied in each of the low consistency and high consistency treatments.
  • about 0.4 to 3.5% by weight preferably about 0.5 to 1.9% for hardwood and 0.75 to 2% for softwood, is applied onto the pulp during each of the low and high consistency alkaline treatments.
  • the alkaline treated pulp 38 is then forwarded to the oxygen delignification reactor 40 where it is contacted with gaseous oxygen 42.
  • Suitable conditions for oxygen delignification according to either the O, O m or 0 S processes comprise introducing gaseous oxygen at about 80 to about 100 psig to the high consistency pulp while maintaining the temperature of the pulp between about 90 and 130°C.
  • the average contact time between the high consistency pulp and the gaseous oxygen ranges from about 15 minutes to about 60 minutes.
  • the partially delignified pulp 44 is forwarded to washing unit 46 wherein the pulp is washed with water 48 to remove any dissolved organics and to produce high quality, low color pulp 50.
  • a first portion 54 of the oxygen stage washer 46 filtrate 52 can be used to advantage in a first shower on the brownstock washer 12. This improves washing and reduces the pressate portion 55 which is used in a second shower on washing unit 12 and later returns into the residual liquor 14 which is sent to the plant recovery without further reuse.
  • a second portion 56 of filtrate 52 is discharged directly to the plant recovery system.
  • a K No. of about 7-10 and a viscosity of above about 13 is readily achieved.
  • a K No. of about 5-8 and a viscosity above about 13 is obtained after the oxygen delignification step.
  • the next step in the process of the invention is ozone delignification and bleaching of the oxygen- delignified brownstock pulp.
  • Treating pulp at high consistencies with ozone without paying particular attention to the comminution of the pulp fibers or to the contact between the individual fibers and the reactant gas stream invariably results in a non-uniform ozone bleaching of the fibers.
  • Such a non-uniform ozone treatment is designated in the prior art with the letter "Z". While the use of a Z stage is not desirable due to the non- uniformities produced, there are situations where the resulting pulp is useful.
  • it is preferred to use a modified ozone technique in which the fibers in a desired size range are uniformly contacted with the ozone gas stream. This ozone treatment has been designated herein as "Z m ".
  • the pulp Prior to treatment with ozone, the pulp is conditioned so as to ensure the most effective selective delignification and to minimize the chemical attack of the ozone on the cellulose.
  • the incoming pulp 50 is directed into a mixing chest 58, where it is diluted to a low consistency.
  • An organic or inorganic acid 60 such as sulfuric acid, formic acid, acetic acid or the like, is added to the low consistency pulp to decrease the pH of the pulp in mixing chest 58 to the range of about 1 to 4 and preferably between 2 and 3.
  • the acidified pulp is treated with chelating agent 62 to complex any metals or metal salts which may be present therein.
  • This chelating step is used to render such metals non-reactive or harmless in the ozone reactor so that they will not cause breakdown of the ozone, thus decreasing the efficiency of the lignin removal and also reducing the viscosity of the cellulose.
  • Preferred chelating agents for this ozone treatment include diethylenetriamine pentacetic acid (“DTPA”) , ethylenediamine tetraacetic acid (“EDTA”) and oxalic acid. Amounts of these chelating agents ranging from about 0.1% to about 0.2% by weight of oven dry pulp are generally effective, although additional amounts may be needed when high metal ion concentrations are present.
  • the acidified, chelated, low-consistency pulp 64 is introduced into a thickening unit 66, such as a twin roll press, for removing excess liquid 68 from the pulp, wherein the consistency of the pulp is raised to a level above about 20%. At least a portion of this excess liquid 68 may be recycled to mixing chest 58 with a remaining portion 68a being directed to the plant recovery.
  • the resultant high consistency pulp 70 is then passed through compaction device 72 such as a screw feeder which acts as a gas seal for the ozone gas and thereafter through a comminuting unit 74, such as a fluffer, for use in reducing the pulp particle size as described below.
  • compaction device 72 such as a screw feeder which acts as a gas seal for the ozone gas
  • a comminuting unit 74 such as a fluffer
  • softwood has been found to be between about 28% and 50%, with the optimum results being obtained at between about 38% and 45% prior to contact with ozone. Within the above ranges, preferred results are obtained as indicated by the relative amount of delignification, the relatively low amount of degradation of the cellulose, and the noticeable increase in the brightness of the treated pulps.
  • the reaction temperature at which the ozone bleaching is conducted is likewise an important factor in the process of the present invention.
  • the maximum temperature of the pulp at which the reaction should be conducted should not exceed the temperature at which excessive degradation of the cellulose occurs, which with southern U.S. softwood is a maximum of about 120°F - 150°F.
  • the pulp be uniformly bleached by the ozone.
  • This uniform bleaching is obtained, in part, by comminution of the pulp into discrete floe particles of a size which is of a sufficiently small diameter and of a sufficiently low bulk density so that the ozone gas mixture will completely penetrate a majority of the fiber floes. Generally, a comminuted pulp particle size of 10mm or less has been found to be acceptable.
  • the particles to be bleached should be exposed to the gaseous ozone bleaching agent by mixing so as to allow access of the ozone gas mixture to all surfaces of the floes and equal access by the ozone gas mixture to all floes.
  • the mixing of the pulp in the ozone gas mixture gives superior results with regard to uniformity as compared to the results obtained with a static bed of floes which results in channeling wherein some of the floes are isolated from the ozone gas relative to other floes and are thereby bleached less than other floes.
  • the oxygen delignified pulp particles 76 Upon exiting fluffer 74, the oxygen delignified pulp particles 76 enter a reactor apparatus 78 adapted for bleaching these particles from a first GE brightness to a second, higher GE brightness.
  • the pulp fiber particles 76 are bleached by the ozone in reactor 78 typically to remove a substantial portion, but not all, of the lignin therefrom.
  • a preferred apparatus comprises a paddle reactor as described in application serial no. 07/604,849 of David White et al. entitled PULP BLEACHING REACTOR, the disclosure of which is expressly incorporated herein by ref rence.
  • an internal conveyor 80 preferably in the form of a rotating shaft 82 to which is attached a plurality of paddle members 84, powered by motor 86, is used to provide intimate contact and mixing between the pulp particles and the ozone gas.
  • These conveying means displace and toss the pulp particles in a radial and forward direction while also inducing the ozone to flow and surround the displaced and tossed pulp particles, to expose substantially all surfaces of a majority of these particles to the ozone. This facilitates substantially complete penetration of all surfaces of these particles by the ozone.
  • the paddles move the pulp in a manner such that it appears to be "rolling” or “lifted and dropped” through the reactor.
  • the pulp is dispersed into the gas phase in the reactor, with the pulp particles uniformly separated and distributed throughout the gas, causing uniform bleaching of the pulp.
  • the overall bleaching rate of the pulp particles is thus significantly improved compared to prior art bleaching methods utilizing fast-reacting gaseous bleaching agents such as ozone.
  • the forward movement of the dispersed pulp approximates plug flow and facilitates a high degree of bleaching uniformity.
  • the reactor is designed to simultaneously control pulp contacting, pulp residence time and gas residence time while effectively consuming up to 99 percent of the ozone. In this way the pulp is bleached to the desired degree while a preferably high conversion of ozone is achieved.
  • the ozone gas which is used in the bleaching process may be employed as a mixture of ozone with oxygen and/or an inert gas, or it can be employed as a mixture of ozone with air.
  • the amount of ozone which can satisfactorily be incorporated into the treatment gases is limited by the stability of the ozone in the gas mixture.
  • Ozone gas mixtures which typically contain about 1-8% by weight of ozone in an ozone/oxygen mixture, or about 1-4% ozone in an ozone/air mixture, are suitable for use in this invention.
  • the ozone gas can be introduced at any position through the outer wall of the shell of the reactor.
  • ozone gas 88 is introduced into the reactor 78 in a manner such that it flows, in one embodiment of the invention, countercurrent to the flow of the pulp.
  • This mixture 96 is directed to ozone generator 98 where the appropriate amount of ozone is generated to obtain the desired concentration.
  • the proper ozone/air or mixture 100 is then directed to reactor vessel 78 for delignification and bleaching of pulp particles 76.
  • Pulp fiber floes 102 after treatment, are permitted to fall into tank 104 from which they can be collected and transported to the peroxide bleaching treatment stage described below.
  • the ozonated pulp Upon completion of the front end of the process, the ozonated pulp, to be acceptable for further bleaching treatment in the process of the application, has a brightness of at least about 59, a K No. of less than about 5 and a viscosity of at least about 9 to 10.
  • pulp 92 exiting the ozone reactor is already of sufficient minimum initial GE brightness (i.e., at least about 59) for further bleaching, in the present invention no intermediate extraction (i.e., E) stage prior to peroxide bleaching is needed.
  • the consistency and pH of the pulp 102 exiting the ozone stage must be adjusted prior to carrying out the peroxide bleaching treatment.
  • the consistency is thus raised to a preferred range of between about 10-15% while the pH of the pulp is adjusted upwardly to ensure a final pH of about 9.5-10.5.
  • a peroxide stabilizing agent selected from sodium silicate, magnesium sulfate, a chelate (such as EDTA or DTPA) or mixtures thereof, is added in an amount sufficient to prevent the undesirable decomposition of the hydrogen peroxide bleaching agent.
  • the preferred stabilizing agent is a mixture of magnesium sulfate and sodium silicate.
  • the stabilizing agents are added on a weight percent basis based upon the weight of the pulp, with preferred ranges of use being up to 3% of sodium silicate, up to 0.2% magnesium sulfate, i.e., as magnesium (Mg ++ ) and up to 0.2% of the chelate.
  • a semi-bleached pulp having a final GEB of about 75 can be produced while, along an alternative path a final pulp product having a GEB of at least about 83-86 can be produced.
  • an ozonated pulp with a GEB of 59-65 is contacted with at least about 0.9%, preferably from about 1-1.5% and most preferably about 1.1% by weight of a peroxide solution, preferably hydrogen peroxide, based upon the weight of the pulp.
  • a peroxide solution preferably hydrogen peroxide
  • the reaction is permitted to continue in a bleaching tower for approximately three hours, with no further mixing of the pulp and peroxide once they are initially combined.
  • the pulp must be at a GEB of at least about 59 prior to the peroxide bleaching stage in order to achieve a final GEB of at least 83.
  • the process for forming GEB pulp of 83+ as described above may be modified by reducing the concentration of the peroxide bleaching agent by about 2/3, i.e., to between about 0.20%-0.65% and preferably about 0.4% by weight of the pulp.
  • the pulp is placed in contact with this material (without additional mixing) for about three hours.
  • the GEB of the ozonated pulp which serves as the starting material must be at least about 59.
  • pulp having an ozone GEB of about 65 is contacted with at least about 0.7% by weight of hydrogen peroxide for a truncated period of about 2-15 minutes, preferably about 5-7 minutes, in contrast to the three hour interval in the procedure described above, with continuous mixing.
  • hydrogen peroxide for a truncated period of about 2-15 minutes, preferably about 5-7 minutes, in contrast to the three hour interval in the procedure described above, with continuous mixing.
  • the ozone stage GEB must be at least about 65 to permit the formation of a semi-bleached pulp of about 75 GEB.
  • the preferred technique combines the truncated process described above (utilizing at least about 0.3% by weight of peroxide) to initially raise the GEB of the pulp by at least about 7 points, and preferably by about 10 points, i.e., to a a GEB of about 70-75, followed by tower bleaching this bleached pulp for about three hours (with from about 0.6% by weight peroxide) so as to obtain a final product having a GEB of at least about 83.
  • the truncated step may be utilized as an initial bleaching stage in the formation of 83+ GEB pulp.
  • the effluent from the final peroxide bleaching stage (i.e., to 83 GEB) is recycled into the ozone delignified pulp prior to the initial bleaching stage.
  • the pulp mixed with fresh peroxide it is also continuously blended with the effluent from the final P- stage.
  • the effluent of the initial stage is discharged.
  • Recycling the effluent from the final bleaching stage to the initial peroxide stage serves two purposes. First, residual peroxide in the bleaching effluent which is recycled may be consumed in the initial stage (see, e.g.. Example 6). Additionally, recycling the effluent to the initial stage helps to boost the ozone pulp brightness level prior to the final peroxide bleaching stage. As a result, the total amount of fresh hydrogen peroxide required in the bleaching operation is significantly reduced, thus providing an economic advantage tied to the use of the process. Peroxide levels in the effluent discharge are also significantly reduced.
  • Bleached pulp with a GE brightness of 83+ can also be produced from ozone delignified pulp with a GEB of 55+, i.e., in contrast to the 59+ GEB pulp used in the systems described above.
  • a Kraft- AQ/O m or 0 S /Z m pulp is subjected to two consecutive three hour peroxide bleaching treatments, each utilizing at least about 0.9% and perferably from about 1-1.5% of peroxide by weight, which increases the ceiling brightness by about 4 points and thus provide a sufficient bleaching action to raise the GEB of the pulp from 55+ to 83+.
  • no extraction is carried out between the ozone and the peroxide stages.
  • the pulp upon exiting the oxygen delignification stage, must have a K No. of 9 or less and a viscosity of at least about 17 cps. This ensures that the pulp retains sufficient strength after oxygen delignification to permit it to withstand the effects of the modified ozone treatment carried out prior to the peroxide bleaching stage.
  • ozonated pulp 102 is passed through washer 106 to remove the by-products 108 of the ozone delignification reaction.
  • the washed, ozonated pulp 110 then enters reaction vessel 112 equipped with agitation means such as impeller 114, wherein it is combined with the hydrogen peroxide bleaching solution 116 for about 2- 15, and preferably 5-7 minutes.
  • Pulp 118 having, for example, a GEB of about 70-75 and an acceptable viscosity of at least about 9 cps, may be removed from reaction vessel 112.
  • the pulp (102a or 120) is treated with water 122 in (optional) washer 124.
  • Effluent 126 from washer 124 may be recycled to washer 106 in order to conserve the peroxide bleaching agent.
  • Washed pulp 128, having a GEB of about 70-75, is transported at a low consistency, i.e., about 10%, to reactor vessel 130.
  • pulp 128 is contacted with the peroxide bleaching agent 132 for about three hours and bleached to a GEB of at least about 83.
  • the consistency of bleached pulp 134 is thereafter raised to about 45% by, for example, pressing in a thickening unit such as twin roll press 136.
  • a portion 138 of this pressate is recycled to reaction vessel 112 for use in the initial bleaching treatment as described above, thus significantly reducing the amount of fresh peroxide 116 which must be added.
  • the final pulp product 148 having an acceptable viscosity of at least about 9 cps and a GE brightness of at least about 83 may thereafter be collected for use.
  • the pulp subjected to the peroxide bleaching sequences described below was initially prepared in the laboratory by a Kraft-AQ/O m /Z m process using laboratory equipment to obtain pulp having appropriate K nos., viscosity and GE brightness values to permit it to be used in subsequent peroxide bleaching stages performed according to the present invention.
  • the bag was then removed from the water bath, the clamp was removed, thereby allowing contact between the pulp and the solution, and the pulp and solution were thoroughly mixed by hand. The bag was then unsealed and excess air was removed to minimize the total volume. The bag was then resealed and returned to the water bath at 80°C.
  • step 5 The mixing procedure of step 5 was repeated at 30 minute intervals throughout the reaction. At the end of the reaction, the bag and contents were removed from the water bath and the temperature was lowered by placing the bag in a room temperature water bath.
  • a total of 10 bags containing eight O.D. grams of pulp were prepared for bleaching, according to the general bag-bleaching procedure set forth above.
  • the amounts of stabilizer added were .85% sodium silicate and .05% magnesium sulfate, while the amount of hydrogen peroxide added was 1.3%. All bags were placed in the water bath at 80°C, allowed to equilibrate, and then were initially mixed according to the general procedure. The bags were then removed at intervals over a 3-hour time period. Tappi handsheets were then made in order to measure the GEB of the bleached pulp.
  • Sodium silicate was added at a level of .67% by weight of the level of hydrogen peroxide used in the sample.
  • Magnesium sulfate (as Mg ++ ) was added at a level of .05% by weight, based on the weight of the O.D. pulp.
  • the hydrogen peroxide concentration was varied from .5% to 2.5% (Table 2) , based on the weight of the pulp.
  • the plastic bags were placed in a hot water bath at 80°C, initially mixed per the general bag-bleaching procedure, and then allowed to react for a total time of three hours.
  • Example 4 By plotting the peroxide ceiling GEB against the ozone GEB, as shown in Fig. 3, one can determine what minimum ozone GEB is required in order to get the final desired peroxide GEB. For instance, in order to achieve a final peroxide GEB of at least 83, an ozone GEB of about 59 or greater is required. In order to get a final perox ⁇ ide GEB of 86, an ozone GEB of about 65 is required. To go from an ozone GEB of about 63 to a peroxide GEB of about 83 requires only about 1% of hydrogen peroxide.
  • Example 4 Example 4 :
  • Both Kraft and Kraft/AQ pulps were prepared uti ⁇ lizing the same (soft) wood chip supply. Approximately 500g of the Kraft/AQ pulp were bleached using the 0 m Z m bleaching sequence. Approximately 500g of the Kraft pulp was bleached using the O m C/DED bleaching sequence.
  • a series of ozone bleached pulp samples were prepared for peroxide bleaching according to the general bag-bleaching procedure set forth above. Varying levels of hydrogen peroxide (Table 5) were added to each plastic bag. The bags were then placed in a water bath at 80°C, allowed to equilibrate to that temperature, removed from the water bath after equilibration, and mixed according to the general bag-bleaching procedure. The samples were allowed to react for about 5-7 minutes and then were removed from the water bath. Tappi handsheets were then made in order to measure the GEB of the peroxide bleached pulp.
  • the filtrate from a three hour peroxide bleaching of a 63.5 GE brightness pulp was recycled to an intermediate peroxide stage wherein it was fortified with additional fresh peroxide to a concentration of 0.3% by weight of the pulp. This solution was applied to the pulp with mixing and was permitted to react therewith for seven minutes. The pulp was then washed and contacted with 0.6% by weight of peroxide in a three hour final stage to 83.3 GE brightness. The dissolved solids from the final peroxide bleaching stage were thus also recycled to the intermediate mixing step.
  • the total peroxide applied to the pulp in the process outlined above is 0.9 (0.3 + 0.6) percent by weight of the pulp. About 0.1% is, however, recovered from the recycle. The amount of fresh peroxide which must therefore be added is about 0.8% by weight. Thus, about 0.2% fresh peroxide is added to the intermediate stage, thus reducing the total amount of fresh chemical required when the recycle process is used.

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Abstract

Procédé de délignification et de décoloration d'une pulpe lignocellulosique sans utiliser de chlore élémentaire ou des composés contenant du chlore, au moyen d'oxygène délignifiant (40) la pulpe pour l'amener à un nombre de K sensiblement égal ou inférieur à 10, une viscosité supérieure à sensiblement 12 cps et une brillance de GE (GEB) située approximativement entre 33 et 43; on délignifie (78) ensuite davantage la pulpe partiellement délignifiée en la soulevant, la déplaçant et la remuant dans un sens radial tout en la faisant avancer dans un sens axial selon un processus semblable à l'écoulement idéal avec une quantité efficace d'ozone (88) pendant une durée suffisante pour obtenir une pulpe pratiquement délignifiée possédant un nombre de K sensiblement égal ou inférieur à 5, une viscosité située au moins entre approximativement 9 et 10 cps et une brillance de GE d'au moins 59 environ. On peut alors éclaircir la pulpe pratiquement délignifiée (102) pour obtenir un produit final dont la brillance de GE est d'au moins 75 approximativement, ou, en variante pouvant atteindre environ 83+, en mettant en contact la pulpe ozonisée avec une quantité suffisante d'un composé de péroxyde pendant une durée ne dépassant pas environ trois heures et en malaxant éventuellement le mélange pulpe/peroxyde.
EP19920904154 1991-01-03 1992-01-02 Procede de blanchiment de pate lignocellulosique sans utilisation de chlore Ceased EP0565625A1 (fr)

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JP (1) JP2002517173A (fr)
BR (1) BR9205490A (fr)
CA (1) CA2099881A1 (fr)
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US5472572A (en) * 1990-10-26 1995-12-05 Union Camp Patent Holding, Inc. Reactor for bleaching high consistency pulp with ozone
BE1006056A3 (fr) * 1992-07-06 1994-05-03 Solvay Interox Procede pour le blanchiment d'une pate a papier chimique.
SE500616C2 (sv) * 1993-06-08 1994-07-25 Kvaerner Pulping Tech Blekning av kemisk massa med peroxid vid övertryck
SE501836C2 (sv) * 1993-09-21 1995-05-22 Sunds Defibrator Ind Ab Blekning av kemisk massa varvid massan behandlas med komplexbildare före och efter ett ozonsteg
SE0004438L (sv) * 1999-12-02 2001-06-03 Andritz Ahlstrom Inc Miljövänlig fiberlinje för framställning av blekt kemimassa
US7001484B2 (en) 2000-05-04 2006-02-21 University Of New Brunswick Peroxide bleaching of wood pulp using stabilizers and sodium hydrosulfide reducing agent
US20070131364A1 (en) * 2005-12-14 2007-06-14 University Of Maine Process for treating a cellulose-lignin pulp
JP5471050B2 (ja) * 2009-06-09 2014-04-16 三菱瓦斯化学株式会社 Ｔｃｆ漂白方法
SE538752C2 (en) * 2014-11-21 2016-11-08 Innventia Ab Process for the production of a treated pulp, treated pulp, and textile fibers produced from the treated pulp

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WO1986004938A1 (fr) * 1985-02-14 1986-08-28 Edward Francis Elton Procede et appareil de delignification alcaline de materiaux fibreux lignocellulosiques
DE4004364A1 (de) * 1990-02-13 1991-08-14 Sueddeutsche Kalkstickstoff Verfahren zur chlorfreien bleiche und delignifizierung von zellstoff
BR9007533A (pt) * 1990-05-17 1992-04-28 Union Camp Corp Processo para fabricacao de polpa alvejada e para deslignificar e alvejar um material lignoscelulosico

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JP2002517173A (ja) 2002-06-11
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FI933057A (fi) 1993-08-13
WO1992012289A1 (fr) 1992-07-23
FI933057A0 (fi) 1993-07-02

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