WO2012015452A1 - Effet de xylanase à faible dose sur la pâte dans un procédé de traitement de blanchiment préalable - Google Patents

Effet de xylanase à faible dose sur la pâte dans un procédé de traitement de blanchiment préalable Download PDF

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Publication number
WO2012015452A1
WO2012015452A1 PCT/US2010/056487 US2010056487W WO2012015452A1 WO 2012015452 A1 WO2012015452 A1 WO 2012015452A1 US 2010056487 W US2010056487 W US 2010056487W WO 2012015452 A1 WO2012015452 A1 WO 2012015452A1
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pulp
xylanase
enzyme
bleaching
treated
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PCT/US2010/056487
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English (en)
Inventor
Caifang Yin
Alfred Trepow
Jacek Kalka
Gopal Goyal
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International Paper Company
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/005—Microorganisms or enzymes
    • 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
    • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
    • D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • 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
    • 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

Definitions

  • This invention relates generally to a pre -bleaching treatment of pulp. More particularly, the invention relates to the effect of low dose Xylanase on pulp in pre-bleach treatment process.
  • Xylanases are used in the pulp and paper industry to enhance the bleaching of pulp and to decrease the amount of bleaching chemicals used in bleaching stages. There have been several mechanisms proposed for the bleaching action of xylanase. One mechanism is that lignin is attached to crystalline cellulose through xylan and xylanase enzymes facilitate bleaching of pulp by hydro lysing xylan, releasing coloured lignin from the pulp. A second proposed mechanism is that xylanase removes xylan thereby improving the alkali extractability of the pulp.
  • xylanase treatment allows subsequent bleaching chemicals such as chlorine, chlorine dioxide, sodium hydroxide, hydrogen peroxide, or combinations of these chemicals to bleach pulp more efficiently than in the absence of xylanase.
  • Pretreatment of pulp with xylanase prior to chemical bleaching increases the brightness and quality of the final paper product and reduces the amount of chlorine-based chemicals which must be used to bleach the pulp. This in turn decreases the chlorinated effluent produced by such processes.
  • a group of xylanase enzymes produced from fungi or bacteria have been practiced by paper industry for pulp prebleaching. It has been demonstrated that using xylanase enzymes in pulp prebleaching reduces total C10 2 consumption by about 10-15% along with a proportional decrease in the caustic usage. Many paper mills have been taking advantage of this non-capital approach to minimize the impact of rising chemical price on the profit.
  • the problems were successfully resolved by simultaneous deployment of the following key strategies in the present invention.
  • the low enzyme dosage is the key factor one out of the three strategies.
  • One aspect of this invention relates to prebleach treatment of pulp with xylanase enzyme prior to chemical bleaching.
  • the unbleached pulp is treated with luminase xylanase up to an amount of about 10-50 g of luminase xylanase per ton of unbleached pulp to enhance subsequent bleaching of the unbleached pulp.
  • the treatment of unbleached pulp is carried out while buffering the unbleached pulp and luminase xylanase with carbon dioxide to a pH of from about 6.5 to about 7.5.
  • Another aspect of this invention relates to a pulp bleaching system having a prebleach treatment of pulp which comprises unbleached pulp and luminase xylanase in an amount from about lOg to about to 13 g per ton of unbleached pulp to enhance subsequent bleaching of the unbleached pulp and carbon dioxide buffering to provide a pH in the prebleach treatment stage from about 6.5 to about 7.5.
  • advantages of some of the embodiments of the process of this invention include 1) reduction of bleaching chemicals such as, C10 2 , H 2 0 2 , NaOH, H 2 S0 4 or any combination of the foregoing, 2) reducing the bleaching cost, 3) reduce steam (energy) consumption, 4) reduce wastewater cooling cost, 5) minimize pulp yield loss, 6) minimize wastewater organic Chemical Oxygen Demand (COD) loading increase to WWTP, 7) improve WWTP efficiency, 8) decrease final effluent COD discharge, 9) minimize the potential impact on paper machine sizing chemistry, 10) high pulp brightness and brightness stability, and/ or 11) a combination of two or more of the aforementioned advantages.
  • Some embodiments of this invention may exhibit one of the aforementioned advantages while other preferred embodiments may exhibit two or more of the foregoing advantages in any combination.
  • a low dosage of luminase xylanase is required in the prebleach treatment of pulp as compared to conventional usage of xylanase in treating pulp that use a higher dosage followed by improved mixing and pH control using acids including carbon dioxide as buffering agent to provide a pH in the prebleach treatment stage from about 6.5 to about 7.5.
  • Chemical Pulp it is meant any type of virgin fiber, secondary fiber, woody or nonwoody fiber, softwood, hardwood or a mixture thereof which has been treated by chemical pulping such as, but not limited to, Kraft pulp, soda pulp or sulfite pulp and is subsequently in a form suitable for bleaching.
  • the chemical pulp comprises virgin fiber.
  • Chemical pulp also includes Kraft pulp, soda pulp or sulfite pulp which has been exposed to an alkali oxygen delignification stage prior to practicing the method of the present invention.
  • Other conditions associated with the production of chemical pulp including Kraft and sulfite pulps are described in Pulp Bleaching: Principles and Practice (edited by Dence and Reeve, 1996; which is herein incorporated by reference).
  • Xylanases has been isolated from a variety of organisms including bacteria and fungi. Xylanase has proven to be a valuable enzyme for the pre-bleaching of pulp to enhance delignification of wood pulp by facilitating the removal of lignin from pulp. Therefore, xylanase prebleaching results in the use of lower amounts of bleaching chemicals as compared to nonenzymatic bleaching.
  • bleaching refers to whitening process carried out on pulps by selective chemical removal of residual lignin and other colored materials, and with minimal degradation of the cellulosic constituents. With respect to secondary fibers, bleaching can also have a dye removal function.
  • the term "Bleaching Chemical” refers to a variety of chemical used in the bleaching of wood pulp such as chlorine (Cl 2 ), sodium hypochlorite (NaOCl), calcium hypochlorite [Ca(OCl) 2 ], chlorine dioxide (C10 2 ), sodium hydroxide, peroxide (H 2 0 2 ), sodium chlorite (NaC10 2 ), Oxygen (0 2 ), Ozone (0 3 ) and others.
  • Bleaching Sequence refers to series of stages, each with specific objectives (e.g., delignification, solubilization, destruction of chromophoric groups), that contribute to an overall whitening effect. Typically the pulp is washed between stages.
  • Kappa Number refers to modified permanganate test value on pulp which has been corrected to 50% consumption of chemical. Kappa number has the advantage of a linear relationship with lignin content over a wide range. For pulp samples under 70% yield, the percent Klason lignin is approximately equal to the Kappa number times a factor of 0.15.
  • Buffer refers to chemical solution that lower pH when acids are added. Such acids include, but not limited to, C0 2 , and H 2 S0 4 .
  • Buffering Action refers to ability to neutralize acids and bases as they are formed during a chemical reaction and thus resist a change in pH.
  • Oxygen Delignification refers to treatment of pulp in alkaline medium with oxygen to degrade and solubilize lignin, typically employed as the first stage of a bleaching sequence or as a bleaching "pre-stage". The process is generally carried out at "medium consistency”. Oxygen is added as a gas and magnesium salts are usually employed as an additive to "protect" the cellulose from degradation.
  • Chlorine dioxide (D) Stages refers to initial delignifying stage (D 0 ) and/or brightening stages (Di and D 2 ) in a bleaching sequence used to produce high-brightness pulp.
  • D 0 initial delignifying stage
  • Di and D 2 brightening stages
  • the highest and most stable brightness is achieved when at least one chlorine dioxide (D) brightening stage is used with an alkaline extraction in between.
  • Alkaline Extraction Stage-(E- Stage) refers to essential stage in any multistage bleaching sequence; it solubilizes the dark- colored chlorinated and / or oxidized lignin compounds formed in the initial acid delignification stage (e.g., chlorination or chlorine dioxide) and in later stages.
  • an E-stage When used prior to the final bleaching stage, an E-stage also serves to "activate" the pulp for more effective brightening.
  • Peroxide Extraction Stage-(Ep- Stage) refers to alkaline extraction stage supplemented with a peroxide agent.
  • Oxidative Extraction Stage-(Eo- Stage) refers to alkaline extraction stage supplemented with an oxidizing agent, most commonly oxygen. Peroxide or hypochlorite may also be used as supplemental chemicals to provide a brightening effect and/or to reduce effluent color.
  • Oxidative peroxide Extraction Stage-(Eop-Stage) refers to alkaline extraction stage supplemented with peroxide and an oxidizing agent.
  • the term “Brightening” refers to 1) any chemical treatment to pulp that increases its brightness. 2) Chemical modification of colored elements in high-yield pulps to render them colorless without removing them, thus retaining the yield advantage of these pulps.
  • COD Chemical Oxygen Demand
  • Biochemical Oxygen Demand refers to amount of oxygen consumed in natural aerobic biological processes.
  • Carryover refers to active or inactive enzyme entrained with the pulp leaving the enzyme treatment stage.
  • Consistency refers to mass or weight percentage of oven dry fiber in a pulp solution, e.g., pulp and water, or stock (pulp and additives) and water. It is expressed as a percentage of this material in the solution, in terms of bone dry (BD), oven dry (OD), or air dry (AD) weight. Consistency is often described qualitatively as low, medium, or high without reference to a standard nomenclature. The following ranges are given as a general guide: very low consistency (0 - 1%), low consistency (1 - 8%), medium consistency (8 - 16%), and high consistency (16 - 40%>).
  • retention time refers to contact period of pulp with a bleaching chemical; usually measured from the point of chemical addition to the point where residual chemical is washed out or displaced by another chemical.
  • the term “Medium-Consistency Centrifugal Pump a.k.a (MC) Pump” refers to a pump which generates localized shear forces high enough to fluidize pulp suspensions up to 15% consistency so that they behave like Newtonian fluids. Air separation and evacuation is an important aspect of pump design, since air would otherwise accumulate in the eye of the pump.
  • the term “Decker or Gravity Thickener” refers to a device for increasing the consistency of dilute fiber suspensions up to the 2-8 percent level, consisting of a rotating screen drum which is wholly or partially submerged in an open vat containing the fiber suspension. Water flows into the cylinder by virtue of the difference in liquid level between the vat and cylinder.
  • a “slusher” or “slush thickener” the stock moves from the inlet side of the vat through the dewatering zone to the other side of the vat where the stock is discharged.
  • pulp is retained on the cylinder and is couched off by a rubber roll.
  • High Density Storage or Buffer Storage refers to large-volume, high-density storage of unbleached or bleached pulp to provide surge capacity between the pulp and paper mills or between sections of the pulp mill, and thus allow for interruptions in either supply or demand. It is also defined as storage of pulp within the 8 to 15%) range of consistency. Description of the invention
  • One aspect of this invention relates to prebleach treatment of pulp with xylanase enzyme prior to chemical bleaching.
  • the unbleached pulp is treated with luminase xylanase in an amount effective up to an amount of about 10-50g of luminase xylanase per ton of unbleached pulp to enhance subsequent bleaching of the unbleached pulp.
  • the treatment of unbleached pulp is carried out while buffering the unbleached pulp and xylanase enzyme with carbon dioxide to a pH of from about 6.5 to about 7.5 and with a good mixing between pulp and luminase enzyme.
  • the prebleach treatment of pulp with lower levels e.g., 10-20 g/t
  • luminase a bacterial-produced endo-P-l,4-xylanase
  • Verenium's Luminase PB-100 and PB-200 a bacterial-produced endo-P-l,4-xylanase enzymes
  • the optimum pH range for prebleaching treatment of pulp with luminase is about 6.8-7.2 (i.e., slightly acidic to slightly neutral) by using acid and preferably carbon dioxide as the pH buffering agent to provide this pH range.
  • a medium consistency (MC) centrifugal pump is required to provide a good mixing of pulp and luminase enzyme.
  • the luminase enzyme can be added to brownstock or post 02 washer repulper or standpipe prior to medium consistency pump (aka, MC pump).
  • Luminase enzyme is most typically added at the suction side of MC pump following the addition of acid or D filtrate for pH control.
  • the Luminase enzyme can be added at the thich stock pump to improve pulp consistency from 10% to 7% consistency.
  • the enzyme treatment is completed in a brownstock High Density (HD) tower or storage tank.
  • HD brownstock High Density
  • one further aspect of the present invention is directed to a process that ensures all enzymes are effectively consumed in the enzymatic treatment of the pulp and/or there is no or substantially no active enzymes present in the pulp composition prior to bleaching of the enzyme-treated pulp.
  • the enzyme-treated pulp composition prior to bleaching may contain from 0 to 50g of active xylanase, preferably from 0 to 40g, more preferably 0 to 30 wt%, and most preferably 0 to 20g of active xylanase per ton of enzyme treated pulp.
  • This range may include less than 0.25, 0.5, 1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50g of active xylanase per ton of pulp transferred to the bleaching step, including any and all ranges and subranges contained therein.
  • Luminase xylanase enzyme outperforms other market xylanase products because of the two key differences between Luminase and market xylanase products: 1) Luminase is produced from bacteria rather than fungi for other market xylanase, and 2) Luminase seems to have better penetration and reactivity than other xylanase products (determined collectively by the enzyme's protein size, shape, and charge).
  • luminase enzyme has made it possible to reduce enzyme dosage that not only improves the net bleaching cost reduction, but provides a mechanism to minimize filtrate COD increase commonly observed in enzyme trials.
  • paper mills used 75-300 g/t enzyme dosage based largely on recommendations from enzyme suppliers. Dropping the enzyme dosage to 10-50 g/t will substantially reduces the net bleaching cost as well as pulp yield loss and bleach filtrate COD increase
  • the temperatures employed in the enzyme treatment stage may vary widely and any temperatures employed in conventional enzyme treatment may be used.
  • useful temperatures can be as low as about 40 °C or lower and as high as about 70 °C or higher.
  • the temperature is usually from about 40 °C to about 70 °C, preferably from about 45 °C to about 65 °C, and most preferably from about 50 °C to about 60 °C.
  • retention time employed in the enzyme treatment stage may vary widely and any retention time employed in conventional enzyme treatment may be used. Usually, retention time will be at least about 30 minutes. Retention times are preferably from about 15 min. to about 240 min., and are more preferably from about 30 minutes to about 240 min. and most preferably from about 40 min. to about 240 min.
  • the consistency (CSC) of the pulp may vary widely and any consistency that provides the desired increase in pulp brightness may be used.
  • the pulp may be treated under low or medium consistency conditions (i.e. from about 2% to about 15% based on the total weight of the mixture of pulp and bleaching chemicals).
  • the consistency is preferably from about 5% to 15%, more preferably from about 8% to 15%, and most preferably from about 10% to about 12%.
  • a washer is disposed after the enzyme treatment step and prior to bleaching to wash the pulp.
  • the washed pulp is then sent to bleaching and the remaining composition may be utilized elsewhere in the process of the invention.
  • the remaining composition may contain enzyme, preferably active enzyme.
  • washing the pulp after the enzyme treatment step removes a substantial portion of the enzyme from the pulp composition after the enzyme treatment step and prior to bleaching.
  • the remaining composition may in part or in whole be recycled for use at any one or more of the aforementioned upstream enzyme addition points described above in the process of the invention including but not limited to the high shower side or the repulper side of the brown stock decker.
  • the remaining composition containing enzyme after washing may be used as a substitute to dilution water that may be mixed with fresh Luminase before entered on the repulper side of the brown stock decker.
  • the remaining composition containing enzyme after washing can be added anywhere between the repulper side of the brown stock decker and/or prior to the enzyme treatment step including but not limited to those enzyme addition points described hereinabove in the process of the invention.
  • Eop stage - Lower Eop stage pH is the key to leverage the bleach filtrate COD.
  • Backing off Eop pH is made possible by effective enzyme treatment particularly with using C0 2 for pH adjustment (better enzyme penetration and efficiency due to more buffered pH with CO 2 ).
  • the reduced Eop pH and temperature also contributes to an improved bleaching cost reduction and a minimum filtrate COD increase.
  • the reduction in the Eop conditions (pH or NaOH charge, temperature and sometime H202 charge) after enzyme treatment is made possible by the functionality of the luminase enzyme to break down the lignin- xylan bonds, making residual lignin more accessible and reactive for removal in the first two delignification (D 0 Eop) stages of the bleach plant.
  • the reduced temperature in the Eop filtrate can improve COD removal efficiency in mill wastewater treatment plant (WWTP).
  • Enzyme pretreatment has allowed the mill to cut all the steam usage off in all of its bleach stages, leading to lower wastewater temperature and improved WWTP operation efficiency.
  • the COD increase is minimized to less than 10% with the help of prebleach washer and by manipulating the enzyme dosage and enzyme application (e.g., C0 2 ) and optimizing D 0 Eop delignification operation conditions (e.g., D 0 C10 2 charge and Eop pH and temperature).
  • the aeration power to increase the dissolved oxygen (DO) level
  • macronutrients nitrogen and phosphorus (N and P) concentrations in the wastewater treatment plant needs to be increased to successfully treat a higher COD enzyme treated effluent and for a higher treatment efficiency.
  • one of the advantages of a preferred embodiment of this invention is the reduction of bleaching chemicals such as C10 2 , H 2 0 2 , NaOH, or combination thereof in the Eop and/ or Ep stages as compared to the same or substantially the same bleaching processes which do not include the enzyme treatment stage.
  • the reduction in the amount of H 2 0 2 is typically at least about 5 %.
  • hydrogen peroxide is used as a bleaching agent in the Eop or Ep extraction stage.
  • the amount of hydrogen peroxide in the bleaching liquor is preferably from about 5 to about 100 pounds per ton of pulp on a dry basis.
  • the hydrogen peroxide is conventionally obtained from suppliers as a mixture of 50 % water and 50 % hydrogen peroxide on a weight basis, but other proportions of water and hydrogen peroxide can be used, provided they are equivalent to from 5 to 100 pounds of H 2 0 2 chemical. These amounts of hydrogen peroxide can be applied to the methods of brightening mechanical as well as chemical pulps according to the present invention.
  • the amount of extraction agent oxidant used e.g. hydrogen peroxide and hypochrite
  • the amount of bleaching agent used is usually at least about 0.2 % based on the dry weight of the pulp.
  • the amount of bleaching agent is from about 0.5 % to about 1 %, more preferably from about 0.5 % to about 0.8 % and most preferably about 0.5-0.8 % on the aforementioned basis.
  • the Eop or Ep pulp brightness and viscosity were higher than those treatments without enzyme treatment, which indicates the positive impact of enzyme treatment on the peroxide efficiency and selectivity in the Ep stage.
  • the viscosity is typically at least about 5 %, preferably at least about 10 %, more preferably from about 5 % to about 15 % and most preferably from about 5 % to about 10 % greater than the viscosity of the pulp made by the same or substantially the same bleaching processes which do not include the enzyme treatment stage.
  • the brightness is typically at least about 2 %, preferably at least about 10 %, more preferably from about 5 % to about 15 % and most preferably from about 7 % to about 10 % greater than the brightness of the pulp made by the same or substantially the same bleaching processes which do not include the enzyme treatment stage.
  • the pH in the D 0 stage of the present invention is higher than the pH of the conventional D 0 bleaching stage.
  • the advantages of higher pH are higher brightness, less AOX formation, elimination of H 2 SO 4 addition and associated BaS0 4 scale formation or a combination of two or more thereof.
  • the pH of the D 0 stage is preferably in the range from greater than 3 to about 6. Any pH within this range can be used.
  • the pH can be as high as about 4, 5, or 6 and as low as about 2.5 to about 3.
  • the pH is from about 3 to about 6.
  • the pH is from about 4 to about 6 and in the most preferred embodiments of the invention, the pH is from about 4.5 to about 5.5.
  • one of the advantages of a preferred embodiment of this invention is the reduction of bleaching chemicals such as C10 2 in the Do stage as compared to the same or substantially the same bleaching processes which do not include the enzyme treatment stage.
  • the reduction in the amount of C10 2 is typically at least about 5 %, preferably at least about 10 %, more preferably from about 5 % to about 20 % and most preferably from about 10 % to about 20 % less than the amount of C10 2 used in the same or substantially the same bleaching processes which do not include the enzyme treatment stage to obtain the same or substantially level of pulp brightness in the Eop and or Ep stages.
  • the amount of extraction agent used e.g.
  • sodium hydroxide, magnesium hydroxide, potassium hydroxide, ect.) used in the practice of the process of this invention can vary widely and any amount sufficient to provide the desired lignin extraction efficiency and the desired degree of brightness can be used.
  • the amount of caustic used is usually at least about 0.5 % based on the dry weight of the pulp.
  • the amount of bleaching agent is from about 1 % to about 8%, more preferably from about 1.5 % to about 3 % and most preferably about 1-2 % on the aforementioned basis.
  • the amount of chlorine dioxide in the Do extraction stage liquor is preferably from about 10 to about 100 pounds per ton of pulp on a dry basis.
  • the chlorine dioxide is conventionally obtained from suppliers as a mixture of 90 % water and 10 % chlorine dioxide on a weight basis, but other proportions of water and chlorine dioxide can be used, provided they are equivalent to from 10 to 100 pounds of C10 2 chemical.
  • These amounts of chlorine dioxide can be applied to the methods of brightening mechanical as well as chemical pulps according to the present invention.
  • the plant source of pulp for use in this invention is not critical and may be any fibrous plant which can be subjected to chemical pulp bleaching.
  • fibrous plants are trees, including hardwood fibrous trees such as aspen, eucalyptus, maple, birch, walnut, acacia and softwood fibrous trees such as spruce, pine, cedar, including mixtures thereof.
  • at least a portion of the pulp fibers may be provided from non-woody herbaceous plants including, but not limited to, kenaf, hemp, jute, flax, sisal, or abaca although legal restrictions and other considerations may make the utilization of hemp and other fiber sources impractical or impossible.
  • the source of pulp for use in the practice of this invention is preferably hardwood and softwood fibrous trees, more preferably Eucalyptus, Spruce and Aspen and is most preferably Aspen and Spruce.
  • the pulp used in the process of this invention can be obtained by subjecting the fibrous plant to any chemical pulping process. Following the wood digestion process, pulp is separated from the spent pulping liquor. The spent pulping liquor is then recovered and regenerated for recycling. The pulp is then bleached and purified in a bleach plant operation.
  • the pulp of this invention can also be used in the manufacture of paper and packaging products such as printing, writing, publication and cover papers and paperboard products.
  • the bleached pulp of this invention or pulp mixtures comprising the bleached pulp of this invention is formulated into an aqueous paper making stock furnish which also comprises one of more additives which impart or enhance specific sheet properties or which control other process parameters.
  • alum which is used to control pH, fix additives onto pulp fibers and improve retention of the pulp fibers on the paper making machine.
  • Other aluminum based chemicals which may be added to furnish are sodium aluminate, poly aluminum silicate sulfate and poly aluminum chloride.
  • wet end chemicals which may be included in the paper making stock furnish for conventional purposes are acid and bases, sizing agents, dry-strength resins, wet strength resins, fillers, coloring materials, retention aids, fiber flocculants, defoamers, drainage aids, optical brighteners, pitch control chemicals, slimicides, biocides, specialty chemicals such as corrosion inhibitors, flame proofing and anti-tarnish chemicals, and the like.
  • the aqueous paper making stock furnish comprising the bleached pulp and the aluminum based compounds is deposited onto the forming wire of a conventional paper making machine to form a wet deposited web of paper or paperboard and the wet deposited web of paper or paperboard is dried to form a dried web of paper or paperboard.
  • Paper making machines and the use of same to make paper are well known in the art and will not be described in any great detail. See for example, Pulp and Paper Chemistry and Handbook for Pulp & Paper Technologies, supra.
  • the aqueous paper making stock furnish containing pulp, aluminum based and other optional additives and usually having a consistency of from about 0.3% to about 1% is deposited from the head box of a suitable paper making machine as for example a twin or single wire Fourdrinier machine.
  • the deposited paper making stock furnish is dewatered by vacuum in the forming section.
  • the dewatered furnish is conveyed from the forming section to the press section on specially-constructed felts through a series of roll press nips which removes water and consolidates the wet web of paper and thereafter to the dryer section where the wet web of paper is dried to form the dried web of paper of this invention.
  • the dried web of paper may be optionally subjected to several dry end operations such as and various surface treatments such as coating, and sizing and calendering.
  • the paper manufactured in accordance with this invention can be used for conventional purposes.
  • the paper is useful as printing paper, publication paper, newsprint and the like.
  • the filtrate COD in the D 0 stage is strictly dependent upon the enzyme application dosage, decreasing with decreasing enzyme dosage. Therefore, one way to manipulate the filtrate COD increase for luminase enzyme treatment is to control the enzyme dosage rate. Luminase enzyme treatment at 10 g/t for birch pulp bleaching actually leads to a 5% decrease in filtrate COD versus about 10% COD increase at the 15 g/t enzyme dosage while achieving the same 20%> of C10 2 and NaOH reduction at both enzyme dosages.
  • Table 1 The process results and conditions are set forth in the following Table 1.
  • the lab results on HW pulps are summarized in Table 2.
  • the luminase enzyme dosage study on HW pulp shows that a luminase dosage at 20 g/t works as well as a high enzyme dosage at 100 g/t.
  • the HW pulp has excellent response to luminase enzyme, resulting in 6 lb/t (20%) C10 2 reduction and 3 lb/t (25%) NaOH reduction with 1-2% higher final brightness and viscosity.
  • Table 2 The process results and conditions are set forth in the following Table 2:
  • Luminase enzyme treatment did not result in a significant change in filtrate COD.
  • a decrease in Eop temperature however leads to a reduced Eop filtrate COD without adversely affecting the Eop efficiency.
  • the luminase enzyme dosage study on pine pulp shows that there is no performance difference between a luminase dosage at 30 g/t and 100 g/t as shown in Table 5
  • the luminase enzyme of pine pulp results in 4 lb/t (15%) C10 2 reduction and 4 lb/t (25%) NaOH reduction with a significantly higher final brightness and viscosity.
  • the process results and conditions are set forth in the following Table 5.
  • the observed filtrate COD increase for both HW pulp and pine pulp is decreased by reducing luminase enzyme dosage and can be further minimized by dropping Eop temperature.
  • Excellent luminase enzyme responses were achieved in lab and mill trial/practice for all the pulps investigated, demonstrating the viability of luminase as a non-capital cost reduction approach for mills provided that the effective luminase enzyme treatment conditions in the brown stock HD can be achieved.
  • the filtrate COD can be minimized by carefully controlling the enzyme dosage, mixing, and pH in the luminase application as well as Eop stage pH and temperature.
  • Xylanase addition and reaction vessel - the luminase xylanase can be added to brownstock or post 0 2 washer repulper or standpipe prior to MC pump. Luminase xylanase is most typically added at the suction side of MC pump following the addition of acid or D filtrate for pH control. The xylanase treatment is completed in a brownstock high density (HD) tower.
  • HD brownstock high density
  • pre-washer pre-bleach plant washer
  • Eo, or Eop Reduction in the extraction (E, Eo, or Eop) stage pH by up to 2 units (to as low as 9) and temperature by up to 20 °C (to as low as 60 °C) as compared with the case without luminase xylanase treatment
  • the luminase xylanase can be added to last brownstock or post 02 washer repulper or standpipe prior to a thick stock pump (aka, TS pump) or a medium consistency pump (aka, MC pump).
  • a thick stock pump aka, TS pump
  • a medium consistency pump aka, MC pump.
  • luminase xylanase is typically added at the suction side of MC pump.
  • luminase xylanase must be added at the last brownstock or post 02 washer repulper to get initial xylanase and pulp mixing followed by adding mechanical action in the TS pump.
  • the pulp consistency can be diluted from typically 10-12% to 7-8% to further help xylanase distribution and mixing.
  • Luminase xylanase may be added to the pulp line following the addition of acid or D filtrate for pH control before being pumped to a brownstock high density (HD) tower or storage tank where the xylanase treatment is completed.
  • HD brownstock high density
  • the acids used for pH control include, but not limited to, C0 2 , H 2 S0 4 , HC1.
  • the buffering agent C0 2 can be added at the inlet (vat) of the washer to reduce the pH of the pulp while simultaneously reducing pulp carryover.
  • C0 2 can be added at the outlet (repulper) of the washer for pH control.
  • a pre-washer will help to practice low-dosage luminase xylanase in three ways: 1) to reduce the unbleached pulp carryover for improved xylanase efficiency (as xylanase preferentially reacts with COD or saltcake carryover in filtrate before reacting with pulp), 2) to recycle residual xylanase, and 3) to allow the pulp mill to send some part of COD to the recovery boiler for burning rather than dumping in a sewer.
  • a washer is disposed after the enzyme treatment step and prior to bleaching to wash the pulp. The washed pulp is then sent to bleaching and the remaining composition may be utilized elsewhere in the process of the invention.
  • the remaining composition may contain enzyme, preferably active enzyme.
  • washing the pulp after the enzyme treatment step removes a substantial portion of the enzyme from the pulp composition after the enzyme treatment step and prior to bleaching.
  • the remaining composition may in part or in whole be recycled for use at any one or more of the aforementioned upstream enzyme addition points described above in the process of the invention including but not limited to the high shower side or the repulper side of the brown stock decker.
  • the remaining composition containing enzyme after washing may be used as a substitute to dilution water that may be mixed with fresh Luminase before entered on the repulper side of the brown stock decker.
  • composition containing enzyme after washing can be added anywhere between the repulper side of the brown stock decker and/or prior to the enzyme treatment step including but not limited to those enzyme addition points described hereinabove in the process of the invention.
  • one aspect of the present invention is directed to a process that ensures all enzymes are effectively consumed in the enzymatic treatment of the pulp and/or there are no or substantially no active enzymes present in the pulp composition prior to bleaching of the enzyme-treated pulp.
  • the enzyme-treated pulp composition prior to bleaching may contain from 0 to 50g of active xylanase, preferably from 0 to 40g, more preferably 0 to 30 wt%, and most preferably 0 to 20g of active xylanase per ton of enzyme treated pulp.
  • This range may include less than 0.25, 0.5, 1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, and 50g of active xylanase per ton of pulp transferred to the bleaching step, including any and all ranges and subranges contained therein.
  • the mill may increase the aeration power to raise the dissolved oxygen (DO) level to >1 mg/1, preferably to >2 mg/1, throughout the aeration basin and to increase macronutrients nitrogen and phosphorus (N and P) addition to the wastewater to successfully treat a higher COD xylanase treated effluent and for a higher treatment efficiency in wastewater treatment plant.
  • DO dissolved oxygen
  • N and P macronutrients nitrogen and phosphorus
  • Xylanase application system The process of making pulp in a pulp bleaching system comprises at least one Do stage and at least one Eop bleaching stage.
  • a prebleach treatment stage comprises pulp and xylanase in an amount of less than 50g of xylanase per ton of pulp.
  • a buffering agent is used for buffering the pulp and xylanase in order to provide a pH in the prebleach treatment stage from about 6.5 to about 7.5.
  • the viscosity is a measurement used to compare a relative strength property of the pulp. This property is used to determine the percentage of hardwood/softwood for making different grades of paper.
  • the Permanganate Number indicates the amount of lignin that is in the pulp. (The Kappa number is generally used only on the brownstock, while the value for the Permanganate Number is comparative to the bleached pulp.)
  • the procedure for determining the Permanganate Number is:
  • Pulp dirt count is done by a visual count of all the dirt spots on the brightness pad and is the size weighted sum of the total dirt spots according to a Tappi temperature rate.

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  • Chemical & Material Sciences (AREA)
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Abstract

L'invention porte sur un traitement de blanchiment préalable de pâte par une enzyme xylanase avant le blanchiment chimique. Un procédé de fabrication de pâte comporte le traitement d'une pâte par une xylanase dans une quantité de moins de 50 g de xylanase par tonne de pâte. L'étape de traitement est effectuée tout en tamponnant la pâte et la xylanase avec un agent de tamponnement à un pH d'environ 6,5 à environ 7,5 avant au moins un stade de blanchiment pour former une pâte traitée.
PCT/US2010/056487 2009-11-11 2010-11-12 Effet de xylanase à faible dose sur la pâte dans un procédé de traitement de blanchiment préalable WO2012015452A1 (fr)

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US26013309P 2009-11-11 2009-11-11
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US61/285,572 2009-12-11
US32360410P 2010-04-13 2010-04-13
US61/323,604 2010-04-13

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CN102877346B (zh) * 2012-10-23 2014-03-12 山东轻工业学院 一种针阔混合硫酸盐化学浆全无氯漂白的工艺
CN104611964B (zh) * 2015-01-15 2016-04-20 陕西科技大学 一种相思木亚硫酸盐法高白度半化学浆的制浆方法
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