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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1042—Use of chelating agents
• • 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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

• This invention relates to the bleaching of lignocellulosic pulp. More particularly, the invention relates to improvements in pulp bleaching.
• Wood is composed of two main parts, namely, a fibrous carbohydrate or cellulosic portion and a non-fibrous portion comprising a complex chemical, commonly referred to as lignin. ⁇
• pulp For use in papermaking processes wood must first be reduced to pulp, which can be defined as wood fibers capable of being slurried or suspended and then deposited as a screen to form a sheet.
• the methods employed to accomplish this pulping usually involve either physical or chemical treatment of the wood, or perhaps some combination of the two processes, to alter its chemical form and to give desired paper properties.
• the wood chips are digested with chemical solutions to solubilize a portion of the lignin and the effect is removal of the lignin.
• chemical solutions to solubilize a portion of the lignin and the effect is removal of the lignin.
• the more usual of these digestive procedures are the sulfite, sulfate or Kraft, soda and modified sulfite processes.
• the resulting material is generally a darkly colored cellulose fiber.
• the dark color is attributable to the fact that not all of the lignin has been removed during digestion and the remaining lignin has been chemically modified.
• This dark pulp is commonly referred to as unbleached pulp. It may pass directly to the papermaking operation if the paper color is unimportant or otherwise, the unbleached lignocellulosic pulps are bleached.
• Bleaching is a term applied to a semi-chemical or chemical step in which the pulp is treated with an active bleaching agent, such as chlorine, chlorine dioxide, ozone, oxygen, hydrogen peroxide, peroxy acids, en2ymes, or a mixture thereof, at a controlled time, temperature, and pH. The desired outcome of these reactions is to brighten the pulp to ever-higher levels of brightness.
• Pulp bleaching is most often a multi-stage process employing chlorine or chlorine- containing compounds such as calcium hypochlorite, sodium hypochlorite and chlorine dioxide.
• chlorine bleaching of lignocellulosic pulps are the processes well known in the art.
• pulp is subjected to a plurality of bleaching, caustic extraction and washing operations to result in bleached, purified and washed pulp of the required brightness and purification.
• the pulp is then discharged from the bleach plant for passage to a pulp dryer to provide dried pulp, and then directly to an on-site paper mill.
• the bleach plant may employ any convenient bleaching sequence such as D 0 EopDiD 2 ,
• OD 0 EopDi, OZEopDiP, CED or DoEC For example, D 0 represents initial delignification with chlorine dioxide solution and E represents alkaline extraction with caustic (in the presence of oxygen and hydrogen peroxide in the case of Eop), C represents reaction with elemental chlorine in acidic medium, Z is ozone, O denotes bleaching with oxygen, P denotes bleaching with hydrogen peroxide, and Dj and D 2 are first and second bleaching stages employing chlorine dioxide. Typically, the pulp is washed after each bleaching and each caustic extraction operation.
• One aspect of this invention relates to an improved bleaching process for bleaching pulp having at least one Eop stage or Ep stage which comprises subjecting the pulp to a Q stage in which the pulp is treated with a chelating agent at a pH of from greater than 2.5 to less than 7 followed by interstage washing prior to treating the pulp in the Eop or Ep stage.
• Another aspect of this invention relates to an improved bleaching process for bleaching pulp comprising a bleaching sequence selected from the group of the formula:
• Q is a stage in which a pulp is treated with a chelating agent at a pH of from greater than 2.5 to less than 7;
• Eop is an extraction stage in which pulp is treated with a composition comprising oxygen, base, and peroxide;
• Ep is an extraction stage in which pulp is treated with a composition comprising base and peroxide.
• Yet another aspect of this invention relates to an improved bleaching process for bleaching pulp comprising a bleaching sequence selected from the group of the formula:
• D 0 is a delignification stage in which pulp is treated with an agent comprising chlorine dioxide preferably no or substantially no elemental chlorine dioxide (ECF).
• ECF elemental chlorine dioxide
• advantages of some of the embodiments of the 5 process of this invention include 1) reduction of bleaching chemicals such as, ClO 2 , H 2 O 2 , NaOH, H 2 SO 4 or any combination of the foregoing, 2) reducing the bleaching cost, 3) low capital requirement, 4) high pulp brightness and brightness stability, 5) higher pulp viscosity, 6) improved bleached plant performance and stability, 7) reduction in filtrate AOX or 8) a combination of two or more of the aforementioned advantages.
• Some embodiments of this invention may exhibit one of 0 the aforementioned advantages while other preferred embodiments may exhibit two or more of the foregoing advantages in any combination.
• the bleaching Eop or Ep stage In this process, less peroxide is required in the bleaching Eop or Ep stage as compared to conventional bleaching process that do not include a Q stage followed by a washing stage to obtain comparable levels of brightness or higher brightness can be obtained using the same5 amount of peroxide in the Eop or Ep stage.
• the present bleaching sequence facilitates the pulp metal profile prior to the Eop or Ep stage to be more conducive to peroxide treatment by selectively removing detrimental metals such as Mn, Fe, and Cu while maintaining beneficial alkaline earth metals such as Mg and Ca.
• the ratio of the Mg and Ca to Mn/Fe/Cu is greatly increased with the O 0 ZQ treatment when compared with the conventional D 0 treatment O given the same specified conditions.
• One aspect of this invention relates to an improved bleaching process for bleaching pulp having at least one Eop stage or Ep stage which comprises subjecting the pulp to a Q stage in which the pulp is treated with a chelating agent at a pH of from greater than 2.5 to less than 7 followed by interstage washing prior to treating the pulp in the Eop or Ep stage.
• the Q stage and following interstage washing can be at any stage in the process provided that Q stage followed by a washing stage or an oxygen delignification stage occurs prior to Eop or Ep stage.
• the Q stage may occur after brownstock washing and at prior to any delignification stage. Thereafter, the pulp can be washed immediately following the Q stage or at any subsequent point prior to the Eop or Ep stage or for example, prior to or after a subsequent D 0 delignification stage.
• the Q stage can also occur after earlier delignification stages as for example an oxygen delignification stage and/or a D 0 delignification stage followed by a subsequent interstage washing prior to the Eop or Ep stage.
• Q stage with interstage washing can be immediately preceding the Eop or Ep stage, or can be separated from these stages by one or more other stages.
• Another aspect of this invention relates to an improved bleaching process for bleaching pulp comprising a bleaching sequence selected from the group of the formula:
• Chelating agents used in the Q stage can be varied widely depending on their effectiveness to bind and hold on (delate) the peroxide detrimental metals mainly Mn at the pH requirement of the Q stage. Any conventional chelating agents can be used for the practice of this invention The selection will be therefore dictated by the effectiveness of the chelants under use conditions.
• useful chelating agent include but are not limited to diethylene triamine pentaacetic acid (DTPA), to aminopolycarboxylic acids (APCA), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), phosphoric acids, ethylenediaminetetramethylene-phosphonic acid (EDTMP),diethylenetriaminepentamethylenephosphonic acid (DTPMP), nitrilotrimethylenephosphonic acid (NTMP), polycarboxylic acids, gluconates, citrates, polyacrylates, and polyaspartates or any combination thereof.
• DTPA diethylene triamine pentaacetic acid
• APCA aminopolycarboxylic acids
• EDTA ethylenediaminetetraacetic acid
• NTA nitrilotriacetic acid
• phosphoric acids ethylenediaminetetramethylene-phosphonic acid
• DTPMP diethylenetriaminepentamethylenephosphonic acid
• NTMP n
• citrates, keto acids, gluconates, heptagluconates, phosphates, and phosphonates also work well in reducing the content of free heavy metal ions in the paper to acceptable levels.
• Preferred chelating agents are DTPA or EDTA and the more preferred chelating agent is DTPA.
• the pH of the Q stage is in the range from greater than 2.5 to about 7.0. 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 3.0 to about 7.0.
• the pH is from about 4.0 to about 7.0.
• the pH is from about 5 to about 6 and in the most preferred embodiments of the invention, the pH is from about 5.0 to about 5.5.
• the consistency (CSC) of the pulp in the Q stage may vary widely and any consistency that provides the desired increase in pulp brightness may be used.
• the pulp may be bleached under low consistency conditions (i.e. from about 3 % to about 6 % based on the total weight of the mixture of pulp and bleaching chemicals), medium consistency conditions (i.e. from about 8 % to about 14 % based on the total weight of the mixture of pulp and bleaching chemicals) or high consistency conditions (i.e. from about 20 % to about 30 % based on the total weight of the mixture of pulp and bleaching chemicals).
• the consistency is preferably from about 3.5% to 30%, more preferably from about 5.5% to 20%, and most preferably from about 6.0% to about 10%.
• the Q stage retention times will vary widely and times used in conventional bleaching stages may be used. Usually, retention times will be at least about 10 minutes. Retention times are preferably from about 10 min. to about 300 min., and are more preferably from about 15 minutes to about 120 min. and most preferably from about 20 min. to about 80 min.
• the Q stage bleaching temperatures employed in the critical bleaching stage may vary widely and temperatures employed in conventional bleaching stages may be used.
• useful temperatures can be as low as about 25 0 C or lower and as high as about 100 0 C or higher.
• the bleaching temperature is usually from about 25 0 C to about 120 0 C, preferably from about 40 0 C to about 100 0 C, more preferably from about 60 0 C to about 90 0 C and most preferably from about 40 0 C to about 50 0 C.
• Pulp washing after the Q stage removes all the or a portion of the chelated metals to protect peroxide used in the subsequent Ep or Eop stage.
• at least about 50% of the chelated metals are removed and in the more preferred embodiments at least about 75% of the chelated metals are removed by washing after the Q stage.
• all or substantially all of the chelated metals are removed by washing after the Q stage.
• interstage washing is immediately after the Q stage.
• the pulp is subjected to extraction in an Eop or Ep stage.
• the Eop stage refers to alkaline extraction of pulp with oxygen (O) and hydrogen peroxide (P)
• Ep stage refers to alkaline extraction of pulp with hydrogen peroxide (P).
• Conventional processes and apparatus can be used in the Ep or Eop stage. See for example "Pulp Bleaching Principles and Practice of Pulp Bleaching” Carlton W. Dence and Douglas W. Reeve, TAPPI Press, 1996 and references cited therein.
• one of the advantages of a preferred embodiment of this invention is the reduction of bleaching chemicals such as H 2 O 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 Q stage.
• the reduction in the amount OfH 2 O 2 is typically at least about 10 %, preferably at least about 60 %, more preferably from about 15 % to about 50 % and most preferably from about 20 % to about 40 % less than the amount OfH 2 O 2 used in the same or substantially the same bleaching processes which do not include the Q stage followed by interstage washing to obtain the same or substantially level of pulp brightness in the Do stage.
• hydrogen peroxide when 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 15 to about 200 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 10 to 200 pounds Of H 2 O 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 chlorine dioxide used in the practice of the process of this invention can vary widely and any amount sufficient to provide the desired degree of brightness can be used.
• 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.
• Another advantage a preferred embodiment of this invention is the reduction of AOX resulting from the Eop and/ or Ep stages as compared to the same or substantially the same bleaching processes which do not include the Q stage.
• the reduction in the amount of AOX is typically at least about 20 %, preferably at least about 30 %, more preferably from about 10 % to about 50 % and most preferably from about 20 % to about 30 % less than the amount of AOX produced in the same or substantially the same bleaching processes which do not include the Q stage to obtain the same or substantially level of pulp brightness in the Eop and/or Ep stages.
• the Eop or Ep pulp brightness and viscosity were higher than those treatments without Q stage, which indicates the positive impact of Q 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
• 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 Q stage.
• a D 0 delignification or other oxidative delignification stages as for example with O 2 , peracetic acid and the like is applied prior to the
• 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 H2SO 4 addition, associated BaSO 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 ClO 2 , H 2 SO 4 , or combination thereof in the DO stage as compared to the same or substantially the same bleaching processes which do not include the Q stage.
• the reduction in the amount of ClO 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 ClO 2 used in the same or substantially the same bleaching processes which do not include the Q 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.
• Another advantage a preferred embodiment of this invention is the reduction of AOX resulting from the D 0 stage as compared to the same or substantially the same bleaching processes which do not include the Q stage.
• the reduction in the amount of AOX is typically at least about 20 %, preferably at least about 30 %, more preferably from about 10 % to about 50 % and most preferably from about 20 % to about 30 % less than the amount of AOX produced in the same or substantially the same bleaching processes which do not include the Q stage to obtain the same or substantially level of pulp brightness in the Do stage.
• the amount of chlorine dioxide in the Do extraction stage liquor is preferably from about 10 to about 200 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 200 pounds of ClO 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 brightness is higher than those treatments without Q stage, which indicates the positive impact of Q treatment on the chlorine dioxide efficiency and selectivity in the Do stage.
• the brightness is at least about 1 %, preferably at least about 2 %, more preferably from about 3 % to about 5 % and most preferably from about 6 % to about 7 % greater than the brightness of the pulp made by the same or substantially the same bleaching processes which do not include the Q stage.
• the other sequences are, for example, D o EopDi, OD o EopDi, D o EopDjD 2 , OD o EopDiD 2 , D o EopDiEpD 2 , OD o EopDiEpD 2 , DEopDiP.
• bleaching process of this invention may include other bleaching stages as for example bleaching with Cl 2 , peroxy acids, chlorine dioxide, ozone and the like, and extraction stages such as extraction with oxygen, ozone, borohydride, chlorine dioxide and the like in the presence other bases such as Mg(OH) 2 .
• Illustrative of such bleaching processes are 0(Do/C Q)Eop, (DoQ)EopD, (DoQ)EOPDD, (D 0 Q)EopED, (D 0 Q)EDEpEopD, ZEQ(Eop)D, ZQ(Eop)D, DoQEpZ(Eop) , DoQEpZD(ZD), D 0 Q(Eop)D(ZD), D 0 Q(Eop)PP, D 0 Q(Eop)DZ, DoQEopDi, ODoQEopD i , DoQEopD , D 2 , ODoQEopD i D 2 , DoQEopD i EpD 2 , ODoQEopD ] EpD 2 , DQEopD i P and the like in which D is as described above and Z is ozone, E is extraction in the presence of base, O is oxygen,
• 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. Illustrative of these products and processes for their manufacture are those described in USP Nos. 5,902,454 and 6,464,832.
• 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.
• Aluminum based chemicals which may be added to furnish are sodium aluminate, poly aluminum silicate sulfate and poly aluminum chloride.
• Other 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 pulp was made from southern hardwood cooked by the Kraft process.
• the unbleached pulp had 10.1 Permanganate number, 26% brightness, and 24 cP viscosity.
• the pulp was bleached in lab with a D 0 EpD and D o /QEpD three-stage ECF (elemental chlorine free) bleaching sequence.
• Each bleaching stage was conducted in sealed plastic bags at the specified conditions (consistency, pH, temperature, and retention time). All pulp samples were preheated to the bleaching temperature, and all the chemicals were added sequentially and mixed thoroughly with the pulp before addition of another chemical.
• the chemical addition sequence in the D stages arc deionized water, acid or caustic (whatever needed for pH control), and ClO 2 .
• the chemical addition sequence was deionized water, caustic, H 2 O 2 , and O 2 .
• the pulp was squeezed to collect filtrate for pH, residual, and COD measurement.
• the pulp was repulped at 1% consistency with deionized water and dewatered on a Buchner funnel and repeat a couple of time to simulate a pulp washing stage in mills.
• the washed pulp was analyzed for brightness, viscosity, and pulp dirt. All the filtrate and pulp analysis was done with the standard published procedures understood by all the people working in the field.
• Table 1 shows the bleaching results and conditions of hardwood pulp on two control ECF bleaching sequences on the left two columns and two D/Q based ECF bleaching sequences on the two right columns.
• Two control ECF sequences (Bleach Nos. 1 & 2) were performed by varying the ClO 2 usage distribution in the Do and Di stage while maintaining the constant total ClO 2 charge. A final pulp brightness of 82% was achieved.
• Two D/Q based ECF bleaching sequences (Bleach No. 3 & 4) were designed with a varying Do stage ClO 2 charge in order to match the performance (final pulp brightness) of the control sequences.
• the organic chelant, DTPA was added to the pulp slurry after the Do stage "as is" without washing.
• the DTPA dosage was 0.15% and the retention time in the Q stage was 30 min.
• Bleach No. 3 and No. 4 had no H 2 SO 4 addition.
• the Do stage pHs were 5.44 and 4.1 1 at 0.8% and 1.1% ClO 2 charges respectively.
• the Q stage pHs were 5.91 and 4.49, respectively, for 0.8% and 1.1% C1O2 charges in the Do stage.
• Example 3 Using the procedure of Example 1, a series of experiment were carried out to determine the effect of D/Q pH and interstage washing on pulp brightness. The process results and conditions are set forth in the following Table 3.
• the Do stages in Bleach No 5 and No 6 were conducted at 5.44 and 4.1 1 pH for 0.8% and 1.1% ClO 2 charges without H 2 SO 4 addition and the Do pulp was subsequently treated with a Q stage at pH 5.91 and 4.11, respectively without washing of the Do pulp.
• the Do stages in Bleach No. 7 and No 8 were conducted at 2.63 and 2.71 pH for 0.8% and 1.1% ClO 2 charges, respectively, by H 2 SO 4 addition and the subsequent Q stages at pH 4.34 and 4.39. Washing was performed after the low pH Do delignification to manage the Q stage toward 5 optimum pH.
• the 2 lb/t (0.1) DTPA is sufficient to produce significant savings in ClO 2 , H 2 SO 4 , and NaOH as good as higher DTPA charges.
• Example 2 Using the procedure of Example 1 , a series of experiment were carried out to determine the effect of the ClO 2 and DTPA addition sequence. The effects of the ClO 2 and DTPA addition sequence are illustrated in Table 5. The process results and conditions are set forth in the following Table 5.
• the AOX filtrate from the D/Q filtrate of Bleach Nos. 3 and 4 and Do filtrate Bleach Nos. 1 and 2 were evaluated using the EPA approved AOX analysis procedure.
• the analysis of the filtrate AOX shows that the AOX concentration in D/Q filtrate was 19.4 ppm as compared with 43.7 5 mg/1 AOX from the Do filtrate.
• the consistency of both D/Q and D stages are the same.
• the total filtrate AOX from DEp and D/QEp sequences are 0.97 kg/ton of pulp and 0.45 kg/ton of pulp, respectively. Therefore, conversion of the current Do stage to D/Q stage has a potential to decrease AOX formation from ECF bleaching by about 50%.
• the reduced AOX formation in D/Q is mainly due to Do (ClO 2 ) delignification at higher pH with some reduction due to reduced 0 ClO 2 usage in the Do stage.
• 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. The results are shown in the following Table 8.
• Table 7 summaries the performance results of the lab (D 0 EpD) case studies for 82% bleached pulp brightness.
• the expected bleached pulp brightness from the DEopD sequence would be 84%.
• the total chemical cost reduction can be achieved by D/QEpD sequence in compared with the lab DEpD control.
• the viscosity of D/QEpD bleached pulp is about three points higher than that of the DEpD control pulp at the same brightness level.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=39315128

Family Applications (1)

Country Status (5)

Cited By (2)

Families Citing this family (3)

Family Cites Families (33)

• 2006
  • 2006-11-15 US US11/599,848 patent/US20080110584A1/en not_active Abandoned
• 2007
  • 2007-11-13 WO PCT/US2007/023771 patent/WO2008060519A2/en not_active Ceased
  • 2007-11-13 CA CA2669032A patent/CA2669032C/en not_active Expired - Fee Related
  • 2007-11-13 BR BRPI0716684-2A2A patent/BRPI0716684A2/pt not_active IP Right Cessation
  • 2007-11-13 EP EP07861951A patent/EP2082095A2/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events