US20070284068A1 - Methods for carbonate pretreatment and pulping of cellulosic material - Google Patents

Methods for carbonate pretreatment and pulping of cellulosic material Download PDF

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US20070284068A1
US20070284068A1 US11/750,101 US75010107A US2007284068A1 US 20070284068 A1 US20070284068 A1 US 20070284068A1 US 75010107 A US75010107 A US 75010107A US 2007284068 A1 US2007284068 A1 US 2007284068A1
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carbonate
recited
pulp
treating
chips
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Raymond Francis
Nam Shin
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Research Foundation of State University of New York
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/222—Use of compounds accelerating the pulping processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/04—Pretreatment of the finely-divided materials before digesting with acid reacting compounds
    • 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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications

Definitions

  • the present invention relates to a process for treating comminuted cellulosic fibrous material, for example, wood chips, with a carbonate pre-treatment prior to cooking the cellulosic material with a cooking chemical in the presence of an anthraquinone (AQ).
  • comminuted cellulosic fibrous material for example, wood chips
  • soda cooking that is, sodium hydroxide [NaOH] as a pulping chemical
  • soda cooking in both batch and continuous digesters.
  • advantages to soda cooking including the ability to raise the design pressure of the recovery boiler to improve the recovery boiler efficiency and the elimination of sulfur in the process.
  • the elimination of sulfur in the cooking process allows for the use of black liquor gasification systems.
  • the use of black liquor gasification results in a power generation increase that is multiple times the power generated using a sulfur-based system.
  • soda cooking includes a lower pulp yield (for both softwoods and hardwoods) than realized by kraft cooking, that is, cooking using sodium hydroxide (NaOH) and sodium sulfide (Na 2 S) as the pulping chemicals.
  • NaOH sodium hydroxide
  • Na 2 S sodium sulfide
  • AQ anthraquinone
  • the volume of NaOH per ton of wood pulp required is higher for SAQ cooking compared to the NaOH required for kraft cooking.
  • This higher volume of NaOH required in SAQ cooking is needed to compensate for the sodium sulfide present in kraft cooking which is not present in SAQ cooking.
  • sodium sulfide (Na 2 S) present in kraft cooking hydrolyzes to NaSH and NaOH and therefore impacts the cooking of the cellulosic material during kraft cooking.
  • the volume of NaOH required in soda AQ cooking is about 20% to 40% higher than in kraft cooking.
  • the higher requirement for NaOH results in higher energy requirements to convert, or causticize, the sodium carbonate (Na 2 CO 3 ) from the recovery boiler to NaOH used in the digester and other parts of the fiber line.
  • hemicelluloses are quickly dissolved in soda, kraft, and SAQ pulping, and that a significant fraction of the applied NaOH is consumed in degrading the hemicelluloses to low molecular weight (MW) products. These low MW organics are difficult to recover from the pulping effluent, referred to in the art as “black liquor,” and they do not have high calorific values. It is also known that the green liquor from the recovery furnace is primarily Na 2 CO 3 when the SAQ process is used.
  • the pulp produced from hardwood material processed using the Lo-Solids® Cooking method with soda-AQ as a cooking chemical can obtain a better terminal brightness than conventional Soda-AQ, but not as bright as pulp produced from kraft cooking.
  • the bleach chemical consumption with Lo-Solids Soda-AQ is better than conventional Soda-AQ for a given final brightness, the pulp still requires a greater quantity of bleaching chemicals than pulp produced by kraft cooking.
  • U.S. Pat. No. 1,887,241 discusses pre-treating, also referred to as pre-cooking, a cellulosic material with sodium carbonate, followed by treating the resulting material with either soda or kraft cooking.
  • pre-treating also referred to as pre-cooking
  • wood chips that have been steamed may undergo this carbonate pretreatment stage at a temperature of about 330 degrees Fahrenheit, that is, about 165 degrees Celsius (C).
  • C degrees Celsius
  • the pretreatment stage using sodium carbonate reduces the quantity of NaOH required. For instance, as disclosed in U.S. Pat. No.
  • 1,887,241 a quantity of 10% sodium carbonate on wood is used along with 15% NaOH, compared to about 25% NaOH added to conventional soda cooking.
  • pretreatment with sodium carbonate at about 165 degrees C. is disclosed in the above-referenced patent, the high temperature treatment disclosed in the '241 patent (published in 1932), for various reasons, has not been accepted in the pulping industry, and is typically not practiced today.
  • the treatment disclosed in '241 patent also does not involve the use of an anthraquinone in any processing step.
  • Recent advantages in the pulping industry include methods for removing silica from cellulosic material using a sodium carbonate containing solution. (See US Application No: 2006/0225852, incorporated by reference herein in its entirety). The methods disclosed in the 0225852 application relate to almost 100% removal of silica contained in cellulosic material, such removal occurring prior to the processing of the fibrous material using conventional methods.
  • aspects of the present invention provide a method for processing cellulose material that overcomes the disadvantages and drawbacks of the prior art methods.
  • some aspects of the present invention provide an avenue for minimizing or eliminating the presence of sulfur from the pulp mill while producing a commercially viable product—a long left, but unresolved need of the Pulping Industry.
  • the present invention in its many aspects, relates to the pretreatment of cellulosic material with carbonate, such as a substantially sulfur-free ( ⁇ 1 g/l total Sulfur) sodium carbonate (Na 2 CO 3 ), followed by cooking the pretreated cellulosic material in the presence of a pulping chemical, such as, sodium hydroxide alone (that is, the “soda” process), but also sodium hydroxide and sodium sulfide (that is, the “kraft” process), or a combination of soda and kraft, and additionally and at least one anthraquinone, i.e. anthraquinone or a substituted anthraquinone, such as 2-methylanthraquinone.
  • carbonate such as a substantially sulfur-free ( ⁇ 1 g/l total Sulfur) sodium carbonate (Na 2 CO 3 )
  • a pulping chemical such as, sodium hydroxide alone (that is, the “soda” process), but also sodium hydroxide and sodium
  • the AQ may be added at anytime during the process. For instance, an AQ may be added to the pretreatment stage, the cooking stage, or even both the pretreatment stage and the cooking stage, as well as before or after each stage. (Addition of AQ to the cooking stage can be performed as described in U.S. Pat. No. 6,569,289, herein incorporated by reference in its entirety).
  • One aspect of the invention is a method of treating comminuted cellulosic fibrous material according to: a) treating the cellulosic fibrous material with a carbonate-containing solution, such as, a substantially sulfur-free carbonate containing solution, to produce a pretreated cellulosic material; b) treating the pretreated cellulosic material with a pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp, wherein, in at least one of a) and b), the cellulosic fibrous material is treated with at least one anthraquinone.
  • a carbonate-containing solution such as, a substantially sulfur-free carbonate containing solution
  • the cellulosic fibrous material may be treated with an anthraquinone in a), b), or both a) and b).
  • the carbonate-containing solution may comprise a sodium carbonate containing solution.
  • the pulping chemical may comprise sodium hydroxide.
  • the active pulping chemical may consist substantially of sodium hydroxide.
  • One aspect of the above method includes additional steps, prior to a), the comminuted fibrous material may be c) treated with an acidic solution, and after c), d) extracting at least some of the acidic solution from the cellulose fibrous material may take place.
  • the method produces a pulp having a lower rejects percent and a higher screened yield percent compared to a pulp produced where a) is not practiced.
  • One aspect of the invention may further include an oxygen delignification treatment as well as at least one bleaching stage, where the method produces a cellulosic pulp having a brightness greater than 88% elrepho.
  • the method may produce a pulp having a lower kappa number after the oxygen delignification treatment at a predetermined screened yield compared to a pulp produced without practicing a).
  • kappa number is used to define the degree of delignification. It refers to the modified permanganate test value of pulp that has been corrected to 50 percent consumption of the chemical.
  • An additional aspect of the present invention relates to a method of treating comminuted cellulosic fibrous material by treating the cellulosic fibrous material with a carbonate containing solution to produce a pretreated cellulosic material, treating the pretreated cellulosic material with a pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp and a liquid containing spent pulping chemical, treating the liquid containing spent pulping chemical to produce a carbonate-containing solution from the spent pulping chemical, and using the carbonate-containing solution produced from the spent pulping chemical as the carbonate containing solution in a) of the method described above.
  • a further aspect of the invention includes a method of treating comminuted cellulosic fibrous material comprising a) treating the cellulosic fibrous material with an acid solution, b) treating the cellulosic fibrous material with a carbonate-containing solution to produce a pretreated cellulosic material, and c) treating the pretreated cellulosic material with a sulfur-containing pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp, where in at least of one of b) and c), the cellulosic fibrous material is treated with an anthraquinone.
  • the sulfur-containing pulping chemical may typically contain sodium hydroxide and sodium sulfide.
  • a still further aspect of the invention comprises a pulp produced from one of the above methods wherein the pulp has a greater yield than produced from prior art methods.
  • FIG. 1 is a schematic diagram of a pulping process according to aspects of the present invention.
  • FIG. 2 is a schematic illustration of a chemical recovery system that can be used in aspects of the invention.
  • FIG. 3 is a plot comparing the screened yield of pulps produced by aspects of the present invention to pulps produced by the prior art.
  • FIG. 4 is a plot comparing light absorption coefficient values of pulps produced by aspects of the present invention to pulps produced by the prior art.
  • FIG. 5 is a schematic illustration of the catalysis of lignin and carbohydrate reactions by anthraquinone as enhanced by aspects of the invention.
  • an improved pulp can be produced by treating comminuted cellulosic fibrous material, such as wood chips, in a first pretreatment stage with a carbonate compound, for example, substantially sulfur-free sodium carbonate, and then in a second pulping stage, for example, soda pulping in the presence of an anthraquinone (AQ used to symbolize any anthraquinones),—an improved pulp can be produced.
  • An improved pulp is also produced if the pulp undergoes an acid treatment prior to a first pretreatment stage, followed by kraft pulping in the presence of an anthraquinone.
  • the pulp produced may be characterized by increased pulp yield, increased bleachability, higher strength, and lower rejects, among other beneficial properties.
  • the amount of pulping chemical required in the pulping process for a desired treatment may be reduced.
  • This development can have a significant impact on attempts to reduce or eliminate the content of sulfur containing pulping chemicals, most notably, sodium sulfide (Na 2 S).
  • sulfur containing pulping chemicals most notably, sodium sulfide (Na 2 S).
  • non-sulfur pulping processes such as, the soda process and the SAQ process, have received limited acceptance in the industry due the relatively poor quality of pulp produced compared to the sulfur-bearing kraft process.
  • typically soda and SAQ processes require a larger amount of pulping chemical, that is, sodium hydroxide (NaOH) compared to the kraft process.
  • NaOH sodium hydroxide
  • An additional aspect of the present invention relates to a method of treating comminuted cellulosic fibrous material includes: treating the cellulosic fibrous material with a substantially sulfur-free carbonate containing solution to produce a pretreated cellulosic material, treating the pretreated cellulosic material with a pulping chemical, such as, an alkaline pulping chemical, for a sufficient time and at a sufficient temperature to produce a cellulose pulp and a liquid containing spent pulping chemical, treating the liquid containing spent pulping chemical to produce a carbonate-containing solution from the spent pulping chemical, and using the carbonate-containing solution produced from the spent pulping chemical as the carbonate containing solution in a) as described above in paragraph 16.
  • the carbonate containing solutions may contain sodium carbonate comprising about 1% to about 12% sodium carbonate as Na 2 O on chips.
  • the above method may also include an oxygen delignification treatment.
  • treating the liquid containing spent pulping chemical includes concentrating the liquid sufficiently to support combustion, burning the concentration liquid to produce a smelt containing carbonate, and, introducing a liquid to the smelt to provide the carbonate containing solution from the spent pulping chemical.
  • a further aspect of the invention includes a method of treating comminuted cellulosic fibrous material comprising a) treating the cellulosic fibrous material with an acid solution, b) treating the cellulosic fibrous material with a carbonate-containing solution, such as sodium carbonate, to produce a pretreated cellulosic material, and c) treating the pretreated cellulosic material with a pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp, where in at least of one of b) and c), the cellulosic fibrous material is treated with an anthraquinone.
  • H-factor refers to a method of expressing cooking time and temperature as a single variable for delignification.
  • FIG. 1 is a schematic diagram of a pulping process 10 employing aspects of the present invention in which comminuted cellulosic fibrous material 12 , for example, wood chips, is treated by a carbonate pretreatment stage 14 and a cooking or pulping stage 16 .
  • comminuted cellulosic fibrous material 12 for example, wood chips
  • carbonate pretreatment stage 14 for example, a carbonate pretreatment stage 14
  • cooking or pulping stage 16 comminuted cellulosic fibrous material 12
  • wood chips is used to facilitate discussion of the invention, aspects of the invention are not limited to treating chips, but may be used to treat any form of comminuted cellulosic fibrous material, including, but not limited to, hardwood chips, softwood chips, sawdust, recycled fibers, recycled paper, agricultural waste, such as bagasse, and other fibrous cellulosic material.
  • chips 12 may typically be conditioned for treatment, for example, steamed, to moisten the chips, heat the chips, and remove as much air and other gases as possible to enhance penetration of the treatment solutions. Steaming of chips 12 may be practiced, for example, in a horizontal steaming vessel or in a Diamondback® steaming vessel, both provided by Andritz Inc. of Glens Falls, N.Y., prior to treatment.
  • chips 12 are treated with carbonate-containing solution 13 , typically a sodium carbonate solution, although potassium and magnesium carbonate solutions may also be applicable.
  • this carbonate containing solution may be substantially free of sulfur.
  • chips 12 are then treated in a second or pulping stage 16 , that is, a cooking stage, with pulping chemical 20 for a sufficient time and at a sufficient temperature to produce a cellulose pulp 18 .
  • Pulp 18 may typically be forwarded for further treatment, for example, to washing, bleaching, or screening, among other conventional treatments.
  • the carbonate-containing solution 13 may be provided by a variety of sources, including, but not limited to, commercially available carbonate and carbonate recovered from a related process, such as, from a chemical recovery cycle (for example, as illustrated in and discussed with respect to FIG. 2 below).
  • the carbonate-containing solution 13 may have a concentration of from about 1% to about 12% carbonate (expressed as Na 2 O) on wood.
  • the carbonate containing solution may have a concentration of from about 2% to about 9% as Na 2 O on wood.
  • the carbonate containing solution may typically be provided as an aqueous solution, that is, as a solution of carbonate in water, though other compounds may be present.
  • a person of ordinary skill in the art would understand the use of the term “about” when describing percent carbonate and will appreciate that it is difficult to have absolute measurements and the use of the term about when describing percent carbonate is ubiquitous in the art.
  • One kg mole of Na 2 CO 3 (106 kg) is equivalent to one kg mole of Na 2 O (62 kg).
  • the carbonate treatment 14 is typically practiced at a temperature of greater than 100 degrees C., for example, between about 120 degrees C. and about 200 degrees. In one aspect, carbonate treatment 14 may be practiced at between about 120 degrees C. and about 170 degrees C., for example, between about 120 degrees C. and about 150 degrees C.
  • a person of ordinary skill in the art would understand the use of the term “about” when describing temperature ranges and will appreciate that it is difficult to have absolute measurements and the use of the term “about” when describing temperature is ubiquitous in the art.
  • treatment 14 may typically be practiced at superatmospheric pressure of about 50 psig to about 150 psig.
  • Pretreatment stage 14 is typically practiced for a sufficient time to provide at least some benefit to the resulting pulp produced in process 10 .
  • pretreatment stage 14 may be practiced for at least 5 minutes, but may be practiced from about 15 minutes to about 6 hours, depending upon the nature of the furnish, that is, the nature of chips 12 , but is typically practiced from about 15 minutes to about 120 minutes.
  • the extracted carbonate-containing liquid 25 may be treated, for example, in a recovery system, disposed of, or otherwise re-used.
  • the carbonate-containing liquid may be recirculated and re-used as the source of or supplement to carbonate 13 .
  • the carbonate pretreated chips 12 are then treated in pulping stage 16 with a pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp 18 .
  • a pulping chemical 20 used in pulping stage 16 may be primarily sodium hydroxide (NaOH), that is, the pulping stage 16 may be “soda” pulping stage.
  • the pulping chemical 20 may comprise NaOH and sodium sulfide (Na 2 S), that is, the pulping stage may be a “sulfate” treatment or “kraft” treatment.
  • the pulping stage comprises a kraft pulping stage
  • the carbonate stage 13 may be preceded by an acid stage 22 (as discussed below).
  • the pulping of pretreated chips 12 is practiced in pulping stage 16 in the presence of at least one anthraquinone (AQ).
  • the pulping of chips 12 in the presence of AQ may be performed as described in U.S. Pat. No. 6,569,289 (the disclosure of which is incorporated by reference in its entirety).
  • the applicants have found that the pretreatment of chips 12 with carbonate, in particular with Na 2 CO 3 , followed by SAQ pulping, provides a pulp 18 having enhanced properties, for example, improved yield, reduced lignin, and improved bleachability, compared to pulps provided by prior art treatments.
  • the experiments performed by the applicants suggest that there may be some synergistic effects in the carbonate or carbonate-AQ pretreatment and pulping process of the present invention that are typically not predictable from the prior art treatments with AQ.
  • At least one AQ is introduced to pretreatment stage 14 , pulping stage 16 , or both stages 14 and 16 .
  • AQ may be provided in its reduced form (that is, a chemical commonly referred to as AHQ, see FIG. 5 ).
  • an aqueous solution of AQ may be introduced to the carbonate pretreatment stage 14 (as indicated by phantom line 17 in FIG.
  • concentration of the aqueous AQ introduced during stage 14 may range from between about 0.01 weight percent to about 0.20 weight percent on chips, but is typically from between about 0.05 and about 0.10 weight percent.
  • AQ can be added anytime during the pulping process as described in FIG. 1 .
  • the AQ may be introduced to the pulping stage 16 (as indicated by line 21 in FIG. 1 ), for example, at the beginning, middle, near the end of the stage, or some combination thereof
  • concentration of the aqueous AQ introduced during pulping stage 16 may range from between about 0.01 weight percent to about 0.20 weight percent on chips, but is typically between from about 0.05 and about 0.1 weight percent on chips.
  • AQ may be introduced to carbonate stage 14 , and omitted from pulping stage 16 ; in another aspect, AQ may be introduced to both carbonate stage 14 and pulping stage 16 .
  • a first treatment stage 14 using a sodium carbonate solution as the carbonate-containing solution for example, a sulfur-free carbonate solution
  • a second pulping stage 16 employing NaOH for example, at a charge of about 13% NaOH on wood
  • AQ that is, a SAQ cooking stage
  • the chips 12 may be treated with an acidic solution 19 in an acid stage 22 (shown in phantom in FIG. 1 ).
  • acid pretreatment 22 may be followed by carbonate treatment 14 .
  • Any acid containing solution may be used for acid 19 , but in one aspect, acid 19 is preferably a non-sulfur containing acid solution, for example, an organic acid (such as, acetic acid) or an inorganic acid (such as, nitric or hydrofluoric acid).
  • stage 22 may be practiced in the presence of a naturally occurring acid, that is, a naturally occurring wood acid.
  • the acid solution 19 may be provided to produce an aqueous environment about chips 12 having a pH of about 6 or below, for example, having a pH of between about 4 and about 6.
  • the acid treatment may be practiced at a temperature greater than 50 degrees C., for example, at about 80 degrees C. to about 160 degrees C.
  • Acid treatment stage 22 is typically practiced for a sufficient time to provide at least some benefit to the resulting pulp produced in process 10 .
  • acid treatment stage 22 may be practiced for at least 5 minutes, but may be practiced from about 30 minutes to about 6 hours, and is typically practiced from about 30 minutes to about 90 minutes, depending upon the nature of the furnish, for example, the pH of chips 12 .
  • the quantity of acid needed may include any amount needed to produce the same effect as 2 to 6% acetic acid at 120° C.
  • the liquid present after acid treatment 22 may be removed or extracted from the chips 12 , as indicated by extraction stage 23 (shown in phantom in FIG. 1 ).
  • the extracted acid-containing liquid 23 may be treated, for example, in a recovery system, disposed of, or re-used.
  • the acid-containing liquid may be re-circulated and re-used as the source of or supplement to acid 19 .
  • the acid treatment may be provided by chips 12 , for example, the acid in stage 22 may be an acid resulting from mature wood (that is, wood which has been in storage for a period of time sufficient to produce an acidic liquor naturally occurring from the wood itself).
  • the acid in stage 22 may be provided by a conventional acid hydrolysis process, for example, a process used to remove metals and other contaminates from the chips 12 .
  • a conventional acid hydrolysis process for example, a process used to remove metals and other contaminates from the chips 12 .
  • One such process is disclosed in U.S. Pat. No. 5,338,366 (the disclosure of which is incorporated by reference herein in its entirety).
  • the chemical consumption (for example, the amount of NaOH required) may be reduced and the bleachability of the resulting pulp 18 enhanced. That is, the amount of bleaching chemical required to achieve a desired brightness, may be reduced compared to prior art treatments.
  • the chemical consumption disadvantages in SAQ cooking can be addressed by the carbonate treatment stage 14 and aspects of the invention may also improve pulp bleachability by oxygen and most likely by other one-electron transfer oxidants, such as, chlorine dioxide, as well.
  • Acid treatment stage 22 (A) may further improve the bleachability of both soda-AQ and kraft pulps, particularly, after an oxygen (O) delignification stage.
  • a kraft green liquor (Na2CO3+Na2S) may be used as the source of carbonate 13 if the pulping process 16 comprises a kraft process.
  • FIG. 2 is a schematic illustration of a chemical recovery system 100 that can be used in aspects of the invention.
  • Chemical recovery system 100 includes a conventional recovery furnace or gasifier 110 for burning concentrated spent cooking liquor 112 , for example, black liquor, to produce a chemical smelt (not shown) containing sodium carbonate and sodium sulfide (when the black liquor comprises kraft black liquor), among other products of combustion of black liquor known in the art.
  • the carbonate containing smelt is dissolved in water in vessel 114 , that is, the green liquor tank, to produce an aqueous solution (known as “green liquor”) containing carbonate.
  • green liquor containing sulfide may be used for the carbonate containing solution when the pulping stage comprises kraft pulping.
  • the carbonate treatment with green liquor may be preceded by an acid treatment (stage 22 of FIG. 1 ) prior to kraft pulping.
  • Vessel 114 may be a green liquor tank or other appropriate vessel as is known in the art.
  • the aqueous sodium carbonate in vessel 144 is typically forwarded for further processing 120 , that is, causticization, to regenerate NaOH to be used for cooking or bleaching, for example, for oxygen delignification.
  • the carbonate in the green liquor in vessel 114 may be used as one source of the carbonate 13 for pretreatment stage 14 described in FIG. 1 .
  • Table 1 summarizes the treatment conditions and the results obtained by a series of laboratory trials using batch digesters.
  • the present invention corresponds to trials 1, 3, and 4 in Table 1 where at least some sodium carbonate is provided in a first treatment stage followed by a soda-AQ (SAQ) pulping stage.
  • Run number 2 is a reference trial which corresponds to a conventional SAQ pulping stage with no carbonate pretreatment
  • run number 5 is a reference trial which corresponds to a conventional kraft cook without AQ.
  • the initial testing approach after the carbonate pretreatment, depressurizing the batch digester (that is, “blowing the digester”) and condensing the carbonate stage off-gases (that is, the effluent).
  • depressurizing the batch digester that is, “blowing the digester”
  • condensing the carbonate stage off-gases that is, the effluent.
  • the NaOH and AQ were added to the condensed effluent and the effluent with NaOH and AQ was re-loaded to the digester with the chip sample.
  • the digester was then heated back up to pulping temperature.
  • Table 1 includes the “H Factor” for the pretreatment and for the cooking stages of the trials. As is know, in the art, H factor normalizes alkaline deliginification rates with temperature of a treatment. Typically, the higher the H factor the more rigorous the treatment. The H factor during the second heat-up is included in the total for the SAQ cooks. Table 1 also provides the pH of the liquor in the digester after the carbonate pretreatment and after the soda-AQ treatment.
  • screened yield is the percent of the original chips present in the pulped chips after treatment and after the pulp has been screened to remove chips, fines, pins, etc, that were not sufficiently pulped in the process and other non-fibrous debris.
  • rejects are an indication of how much of the original chips were not fully cooked by the process, for example, as isolated by screening. The lower the rejects the less wood is discarded or re-treated.
  • kappa number provides a relative indication of the amount of undesirable lignin present in the resulting pulp.
  • the higher the kappa number the more lignin present in the pulp and the more bleaching chemical required to achieve a desired bleached brightness.
  • a lower kappa number is preferred.
  • the data in Table 1 supports advantages of the present invention.
  • the data provided in Table 1 illustrate that the method shown in FIG. 1 offers a dramatic improvement in conventional soda-AQ pulping.
  • the reject values are the clearest indication of the advantage of aspects of the present invention.
  • run number 4 corresponding to carbonate pretreatment and soda-AQ pulping—provides a value of 0.3 for rejects and a screened yield of 55.3%.
  • run number 2 representing the prior art SAQ pulping—provides a value of 27.0% for rejects and a significantly lower screen yield of 28.4%. This implies that aspects of the present invention more efficiently cook more of the chips to produce a pulp while retaining a significant portion of the cellulose as evidenced by the high yield.
  • run number 2 (corresponding to the prior art SAQ process) provides a lower SAQ end pH than runs 1, 3, and 4 (representing aspects of the invention) even though the NaOH application was 10% Na 2 O on wood in all four cases.
  • the applicants theorize that the lower pH of the prior art SAQ process is due to NaOH, a stronger base, out-competing Na 2 CO 3 in wasteful carbohydrate degradation reactions.
  • the Na 2 CO 3 remains in solution in SAQ cooking and is not a strong enough base to cause the alkaline rearrangements necessary for lignin depolymerization and solubilization.
  • Cooking without carbonate pretreatment was also investigated in laboratory trials to provide a basis for comparison with the aspects of the present invention.
  • the results of these trials are summarized in Table 2.
  • a series of kraft and SAQ pulps were prepared from sugar maple chips without carbonate pre-cooking.
  • One of the kraft pulping trials was made with a higher sulfidity and lower effective alkali (10% Na 2 O on chips from NaOH and 5% Na 2 O on chips from Na 2 S), see the second line of data in Table 2.
  • This kraft pulping trial (second line in Table 2) provided a higher screened yield (approximately 1.0% higher screened yield on chips) compared to a kraft trial with a higher EA, that is, 12% Na 2 O on chips from NaOH and 4% Na 2 O on chips from Na 2 S (see the first line of data in Table 2). Both pulps had approximately the same unbleached kappa number (that is, 17.4 and 17.8). However, the pulp produced using the lower EA (that is, 10% NaOH and 5% Na 2 S, in the second line of Table 2) appeared to be less responsive to oxygen (O 2 ) delignification than the pulp produced with higher EA (12% NaOH and 4% Na 2 S), as will be discussed below.
  • Carbonate precooking according to one aspect of the invention was investigated in lab trials. The results of these trials are summarized in Table 3.
  • Table 3 provides the treatment conditions for pretreating chips with carbonate followed by a SAQ treatment (runs 1-5) and by a kraft treatment (runs 6 and 7).
  • the advantages of carbonate precooking according to aspects of the invention are evident by comparing the results presented in Table 2 (the prior art) to those presented in Table 3. For instance, if run 1 in Table 3 is compared to the conventional SAQ in Table 2 (the fifth line of Table 2) it can be seen that a 30 minute carbonate stage at 165° C.
  • aspects of the present invention may also result in an H-factor decrease in the cooking stage that is greater than would be expected.
  • H-factor provided in the treatment performed without carbonate pretreatment is higher than the total H factor for carbonate pretreatment plus cooking to the same kappa number.
  • the H factor for pulp that was not pretreated was over 1600 for SAQ.
  • the H factor for the SAQ stage for the first two carbonate (C 1 ) pretreated pulp (runs 1-2 in Table 3) was 1239, and the C 1 stage H factor was 358 for a total of 1597 for the combined carbonate and SAQ treatments.
  • the cellulosic material was bleached.
  • the bleaching sequence used in the laboratory test was an OD 0 EpD 1 (where O is alkaline O 2 stage; D 0 is chlorine dioxide delignification with an end pH of 2-3; Ep is alkaline extraction with sodium hydroxide and hydrogen peroxide for incremental delignification; D 1 is a chlorine dioxide brightening with an end pH of 3.4-4.5).
  • the applicants found that the 21.5 kappa number pulp produced in the soda-AQ pulp trial (that is, the data in the fourth line of Table 2) could be produced with 12.5% Na 2 O; however, this pulp was more difficult to bleach than the pulp produced when 14.0% Na 2 O was used (that is, the data in the fifth and sixth lines of Table 2).
  • the kappa number decrease due to O 2 is typically an indicator of the ease of bleachability.
  • the bleachability of a soda-AQ pulp is improved by the carbonate pretreatment.
  • any suitable known bleaching process can be used, including bleaching processes that eliminate chlorinated compounds, that is, totally chlorine free (TCF) bleaching processes a eliminatel elemental chlorine, that is, elemental chlorine free (ECF) bleaching processes.
  • TCF totally chlorine free
  • ECF elemental chlorine free
  • FIG. 3 provides a plot of a comparison of screen yield as a function of post oxygen delignification kappa number for aspects of the present invention and the prior art.
  • aspects of the invention provide a pulp that is more easily bleached compared to conventional prior art methods.
  • screen yield percent is a ratio of the weight of the output pulp of the process over the weight of the input wood to the process after the output pulp has been screened to remove knots, shives, and other unwanted material. A higher screen yield is preferred.
  • the O 2 kappa number relates to the lignin content of the cooked and oxygen-delignified pulp. As is known in the art, a lower kappa number is preferred. With regard to FIGS.
  • Methods of the present invention further include an oxygen delignification treatment resulting in a pulp having a lower kappa number after the oxygen delignification treatment at a predetermined screened yield compared to a pulp produced by the method without practicing a pretreatment stage 14 .
  • the O 2 kappa number for C-SAQ (“X”) is just over 8 kappa with a screened yield percent of over 52% and the O 2 kappa number for SAQ (“ ⁇ ”) is approximately 10.5 kappa with a comparable screened yield of approximately 52.5%. That is, at comparable screened yields, an aspect of the present invention provides a lower kappa number compared to the prior art. Therefore, the carbonate treatment decreases the kappa number (both unbleached and after the O stage).
  • FIG. 4 provides a plot of a comparison of fully bleached pulp as a function of post oxygen delignification kappa number for aspects of the present invention and the prior art.
  • the ordinate in FIG. 4 is the light absorption coefficient (LAC) value for the fully bleached pulp after OD 0 EpD 1 bleaching and the abscissa is the post O 2 kappa number.
  • LAC light absorption coefficient
  • a review of FIG. 4 reveals that the conventional soda-AQ pulps (“ ⁇ ”) contain more color (that is, have a higher LAC values) than kraft pulps (“closed diamond”).
  • the soda-AQ pulp after acid (A) and carbonate (C) pretreatments (“open triangle” and “open diamond”) according to aspects of the invention had equal or slightly lower color content than kraft pulps without pretreatments.
  • At least some of the A-stage (acid stage) effluent may be displaced, for example, 50% to 75% of the total A stage effluent, with the carbonate-containing solution.
  • at least some and possibly all of the carbonate stage effluent may be transferred with the chips into the kraft or SAQ stage.
  • the carbonate stage effluent was recovered after passing through a condenser. The NaOH was introduced to the effluent as pellets and AQ powder was dissolved in the condensed effluent. The carbonate and AQ containing effluent was then returned to the lab digester for the SAQ stage. Sodium sulfide solution and NaOH pellets are added to the carbonate stage effluent in the case of kraft pulping.
  • brightness is percent elrepho.
  • the carbonate stage effluent may be important to aspects of the invention, for example, to the carbonate-SAQ process.
  • the carbonate effluent may contain many low molecular weight carbohydrates with reducing end groups. It is estimated that carbohydrate dissolution during the carbonate stage may be approximately 5% of the original chip mass (oven dry basis).
  • carbohydrate dissolution during the carbonate stage may be approximately 5% of the original chip mass (oven dry basis).
  • random hydrolysis of the carbohydrates would be expected and formation of a new reducing end group is likely with each hydrolysis.
  • the higher concentration of reducing end groups would reduce AQ at a higher rate to form AHQ (anthrahydroquinone), that is, the active delignification catalyst.
  • AHQ anthrahydroquinone
  • the AQ/AHQ catalytic cycle is shown schematically in FIG. 5 .
  • a reducing end group in the solid phase is oxidized to a carboxylic acid it becomes resistant to the alkaline peeling reaction that lowers the molecular weight of carbohydrates and decreases pulp yield.
  • the hypothesis above may explain why the carbonate stage improves pulp yield for SAQ pulping, but not for kraft pulping.
  • the oxidation of reducing end groups to carboxylic acids is not known to be a significant reaction (or even occur) in the kraft process, or the soda process without AQ addition.
  • the A 1 pretreatment provided a soda-AQ pulp with higher bleached (that is, “Final”) brightness (90.8) than kraft (89.9), but pulp yield was somewhat lower.
  • the milder A 2 pretreatment with an acid carbonate-SAQ provided a higher pulp yield (54.2%) than both conventional kraft pulping and SAQ pulping.
  • the A 2 C-SAQ treatment also afforded a higher bleached brightness (89.2) than SAQ pulping (88.4) but less than kraft pulping (89.9).
  • the applicants believe that that the severity of the acid (A) stage may preferably be higher than the A 2 acid treatment, but lower than the A 1 acid treatment for this chip furnish.
  • the combined H factor for the carbonate (C) and soda-AQ stages in run 5 is 897 (81+816) produced a pulp having approximately the same kappa number (23.1 vs. 22.6), higher yield (55.8 vs. 54.2) and lower rejects (0.6 vs. 1.0) compared to a prior art SAQ produced pulp without the pretreatment but with a H factor of 992 (run 9).
  • Time spent in the carbonate stage may have a significant impact on the resulting pulp.
  • an additional 30 minutes in the carbonate stage at pH ⁇ 8 resulted in a 1.6 kappa unit advantage after soda-AQ and oxygen delignification.
  • the extra 30 minutes in the carbonate stage afforded a higher screened yield.
  • aspects of the invention can be performed in equipment for a batch (such as but not limited to conventional, SuperBatch® or Rapid Displacement Heating) or continuous (such as but not limited to conventional soda, conventional kraft, Lo-Solids® Cooking, EMCC® Cooking, ITC® Cooking, and Compact Cooking) where pressurized equipment (as required for the carbonate treatment) is used for any or all of the stages of acid, carbonate and cooking.
  • a batch such as but not limited to conventional, SuperBatch® or Rapid Displacement Heating
  • continuous such as but not limited to conventional soda, conventional kraft, Lo-Solids® Cooking, EMCC® Cooking, ITC® Cooking, and Compact Cooking
  • pressurized equipment as required for the carbonate treatment
  • aspects of the invention are also amenable to pretreatment during transport or storage of comminuted fibrous material, for example, as described in U.S. Pat. No. 655,462, the disclose of which is incorporated by reference herein.
  • conventional means such as pumping of liquor into the vessel can be used to displace the liquid in the digester, or the liquor can be discharged from the digester by inherent pressure or pump-out means, before the new cooking liquor is added to the digester.
  • All liquids can be preheated using methods known in the art, such as extracted liquor from SuperBatch or RDH methods. Further, heating of the liquid can be accomplished in the vessel by circulation loops or direct steam addition.
  • aspects of the present invention provide cellulosic material pretreatment process and pulping process that provides advantageous improvements to prior art treatments of wood chips, and related comminuted cellulosic materials.
  • pretreatment of wood chips with a carbonate solution, with or without the presence of an anthraquinone can produce cellulose pulps that are higher in yield, lower in rejects, greater in strength, and require less chemical to both produce and bleach.

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US20090221814A1 (en) * 2008-02-28 2009-09-03 Andritz Inc. System and method for preextraction of hemicellulose through using a continuous prehydrolysis and steam explosion pretreatment process
US20100263813A1 (en) * 2009-04-21 2010-10-21 Andritz Inc. Green liquor pretreatment of lignocellulosic material
US20110094692A1 (en) * 2008-03-18 2011-04-28 The Research Foundation Of State University Of New York Methods of pretreating comminuted cellulosic material with carbonate-containing solutions
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CN103764903A (zh) * 2011-08-30 2014-04-30 嘉吉公司 制浆方法
RU2649301C2 (ru) * 2012-12-12 2018-03-30 Басф Се Применение дитионита натрия в процессе варки целлюлозы

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US8262856B2 (en) * 2007-06-18 2012-09-11 Andritz Inc. Processes and systems for the bleaching of lignocellulosic pulps following cooking with soda and anthraquinone
US20090221814A1 (en) * 2008-02-28 2009-09-03 Andritz Inc. System and method for preextraction of hemicellulose through using a continuous prehydrolysis and steam explosion pretreatment process
US8512512B2 (en) 2008-02-28 2013-08-20 Andritz Inc. System and method for preextraction of hemicellulose through using a continuous prehydrolysis and steam explosion pretreatment process
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US20140102648A1 (en) * 2011-03-22 2014-04-17 Andritz Oy Method and arrangement for treating chemical pulp
CN103764903A (zh) * 2011-08-30 2014-04-30 嘉吉公司 制浆方法
RU2649301C2 (ru) * 2012-12-12 2018-03-30 Басф Се Применение дитионита натрия в процессе варки целлюлозы

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WO2007137127A3 (en) 2009-05-07
CA2651483C (en) 2013-06-18
RU2008150352A (ru) 2010-06-27
AU2007253774C1 (en) 2012-03-22
BRPI0711473A2 (pt) 2011-11-16
RU2445414C2 (ru) 2012-03-20
WO2007137127A2 (en) 2007-11-29
CA2651483A1 (en) 2007-11-29
JP2009537705A (ja) 2009-10-29
AU2007253774A1 (en) 2007-11-29
AU2007253774B2 (en) 2011-10-06
JP5207191B2 (ja) 2013-06-12
EP2061927A2 (en) 2009-05-27

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