JP2009537705A - Method for carbonate pretreatment and pulping of cellulosic materials - Google Patents

Abstract

  A method of treating a pulverized cellulosic fibrous material, treating with sodium carbonate, and then cooking the pretreated material in the presence of anthraquinone (AQ). The pulp produced thereby has a higher yield, stronger strength and better bleachability compared to pulp produced by the prior art. AQ can be introduced at the carbonate pretreatment stage. This method can further include an acid pretreatment, resulting in enhanced properties due to the pulp produced.

Description

  The present invention is for treating a ground cellulosic fibrous material, such as wood chips, with a carbonate pretreatment before cooking the cellulosic material with cooking chemicals in the presence of anthraquinone (AQ). Concerning the method.

  In the field of chemical pulping, cellulosic materials such as wood chips are treated with pulping chemicals to produce pulp that is used in the manufacture of paper and other products. It is well known in the art to use caustic soda (ie, sodium hydroxide [NaOH] as pulping chemical), called soda cooking, in both batch and continuous digesters. Soda digestion has many advantages, including increased recovery boiler design pressure and improved recovery boiler efficiency and sulfur removal in the process. Among other benefits, the removal of sulfur in the cooking process allows the use of a black liquor gasification system. As a result of the use of black liquor gasification, the amount of power generation is many times greater than the power generated using the sulfur-based system.

One of the drawbacks of soda digestion, kraft cooking, i.e., than those achieved by digestion with sodium hydroxide (NaOH) and sodium sulfide (Na 2 _S) as a pulping chemical, is a low yield of pulp (For both coniferous and hardwood). However, the addition of anthraquinone (AQ) to soda cooking has been shown to improve the pulp yield and thus the pulp yield is comparable to that of kraft cooking. However, even when AQ is added, the pulp obtained from the soda cooking process has weaker pulp strength and insufficient bleaching than kraft cooking.

However, as compared to kraft cooking, soda anthraquinone (SAQ) cooking also has drawbacks. For example, SAQ cooking requires a greater amount of NaOH and it is more difficult to bleach the pulp produced from the SAQ pulping process. For example, the more NaOH required, the more recausticization is required. As is known in the art, re-causticization of sodium carbonate to regenerate NaOH proceeds as shown in Equations 1 and 2 below.
Formula _{1: Na 2 CO 3 + CaO} + H 2 O → 2NaOH + CaCO 3
Formula 2: CaCO ₃ → CaO + CO ₂

The required volume of NaOH per ton of wood pulp is higher in the case of SAQ cooking compared to that required for kraft cooking. The higher volume of NaOH required for SAQ cooking is necessary to make up for the sodium sulfide present in kraft cooking but not in SAQ cooking. As is known in the art, sodium sulfide (Na ₂ S) present in kraft cooking hydrolyzes to NaSH and NaOH, thus affecting the cooking of cellulosic materials during kraft cooking. The volume of NaOH required for soda AQ cooking is about 20% to 40% higher than kraft cooking. The higher the requirement for NaOH, the more the energy requirements for converting or causticizing sodium carbonate (Na ₂ CO ₃ ) from the recovery boiler into the NaOH used in the steamer and other parts of the fiber line. Get higher.

For example, when using active alkali (AA = NaOH + Na ₂ S (based on Na ₂ O)) with 16.0% Na ₂ O and 30% sulfidity for kraft pulping, 11.2% of AA is derived from NaOH Yes, 4.8% of AA is derived from Na ₂ S. In kraft recovery, if all of the sulfur is recovered as Na ₂ S, re-causticization is needed to convert it to NaOH so that the desired 11.2% Na ₂ O is realized on the new chip. It is done. Hardwood SAQ pulping requires the same effective alkali (EA = NaOH + 1 / 2Na ₂ S (Na ₂ O base)) as kraft pulping. In the above example of kraft pulping, EA had 13.6% Na ₂ O, but a similar amount of alkali is considered necessary for SAQ pulping, all of which is considered to be derived from NaOH.

Furthermore, it is well known that hemicellulose dissolves quickly in soda, kraft, and SAQ pulping, and a significant amount of added NaOH is consumed to break down hemicellulose into 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 do not have a high calorific value. It is also known that the green liquor obtained from the recovery furnace is mainly Na ₂ CO ₃ when the SAQ process is used.

  Lo-Solids® cooking method (US Pat. Nos. 5,489,363; 5,536,366; 5,547,012, which are incorporated herein by reference in their entirety); No. 5,620,562; No. 5,662,775; No. 5,824,188; No. 5,849,150; No. 5,849,151; No. 6,086,712; , 132,556; 6,159,337; 6,280,568; 6,346,167) and using soda-AQ (SAQ) as cooking chemical Pulp obtained from processed hardwood material has been shown to result in pulp having better strength than that produced by conventional kraft cooking. Furthermore, pulp produced from hardwood material, processed using the Lo-Solids® cooking method with soda-AQ as the cooking chemical, has a better final whiteness than conventional soda-AQ. Can be obtained, but not as white as pulp produced from kraft cooking. Although bleach chemical consumption by Lo-Solids soda-AQ is better than conventional soda-AQ for a given final brightness, the pulp still has a higher bleaching chemistry than pulp produced by kraft cooking. Requires chemicals.

  For these and other reasons, kraft cooking (and its many sulfur related problems) is a widely used pulping process in the industry. However, Applicants overcome the drawbacks of SAQ pulping by pretreating the cellulosic material with a carbonate solution that is substantially free of sulfur (<1 g / l total sulfur) and then performing SAQ. I found out that I can.

  U.S. Pat. No. 1,887,241 (incorporated herein by reference in its entirety) performs a pretreatment, also called pre-cooking, with sodium carbonate on cellulosic material, after which the resulting material is soda. Or discussing kraft cooking. In the process disclosed in the '241 patent, steamed wood chips can be subjected to this carbonate pretreatment at a temperature of about 330 degrees Fahrenheit, that is, a temperature of about 165 degrees Celsius (C). . According to the '241 patent, the pretreatment step using sodium carbonate reduces the amount of NaOH required. For example, as disclosed in U.S. Pat. No. 1,887,241, conventional soda cooking adds about 25% NaOH to 15% NaOH and 10% carbonate to wood. Sodium is used. Pretreatment with sodium carbonate at about 165 ° C. is disclosed in the aforementioned patent, but the high temperature treatment disclosed in the '241 patent (published in 1932) has been accepted by the pulping industry for a variety of reasons. This is not currently done. Also, the processing disclosed in the '241 patent does not use anthraquinone at any processing stage.

  A recent useful technology in the pulp industry is a method for removing silica from cellulosic materials using a sodium carbonate-containing solution (the US, which is incorporated herein by reference in its entirety, Application No. 2006/0225852). The method disclosed in the 0225852 application relates to the removal of almost 100% of the silica contained in cellulosic materials, such removal prior to processing of the fibrous material using conventional methods. Done.

  Embodiments of the present invention provide a method for processing cellulosic material that overcomes the shortcomings and difficulties of the prior art methods. For example, some aspects of the present invention may minimize or eliminate the need to remain long-standing in the pulping industry and not yet solved, i.e., the presence of sulfur from pulp mills, while at the same time commercializing. A means for producing a practically feasible product is provided.

Many aspects of the present invention pre-treat the cellulosic material with a carbonate such as sodium carbonate (Na ₂ CO ₃ ) that is substantially free of sulfur (<1 g / l total sulfur), Thereafter, additionally and at least with pulping chemicals such as sodium hydroxide alone (ie, “soda” process), or sodium hydroxide and sodium sulfide (ie, “kraft” process), or a combination of soda and kraft. It relates to cooking a pretreated cellulosic material in the presence of one anthraquinone, ie a substituted anthraquinone such as anthraquinone or 2-methylanthraquinone. AQ may be added at any point during the process. For example, AQ may be added in the pretreatment stage, the cooking stage, or both the pretreatment stage and the cooking stage, and before or after each stage (addition of AQ to the cooking stage is entirely incorporated by reference. Can be performed as described in US Pat. No. 6,569,289, incorporated herein).

  One aspect of the present invention is a method of treating a pulverized cellulosic fibrous material comprising: a) a carbonate-containing solution, such as a carbonate-containing solution substantially free of sulfur, wherein the cellulosic fibrous material. B) producing a pretreated cellulosic material, b) using the pulping chemicals at a sufficient time and at a sufficient temperature to produce the pretreated cellulosic material. The method comprises a step of treating, wherein at least one of a) and b), the cellulosic fibrous material is treated with at least one anthraquinone. In this method, the cellulosic fibrous material may be treated with anthraquinone in a), b), or both a) and b). In one aspect, the carbonate-containing solution can comprise a sodium carbonate-containing solution. In another aspect, the pulping chemical may consist of sodium hydroxide. Furthermore, the active pulping chemical can consist essentially of sodium hydroxide.

  One aspect of the above method comprises an additional step before a), wherein the ground fibrous material is treated with c) an acidic solution, and after c) d) of the acidic solution from the cellulose fibrous material. At least a part of it can be extracted.

  In another aspect, the method produces a pulp having a lower percent defective and a higher post-screening yield compared to the pulp produced when a) is not performed.

  One aspect of the present invention may further comprise an oxygen delignification treatment as well as at least one bleaching stage, the method producing a cellulosic pulp having a whiteness higher than 88% errefo. When oxygen delignification treatment is performed, this method produces a pulp having a lower kappa number after oxygen delignification treatment with a predetermined post screen yield compared to pulp produced without a). be able to. As is known in the art, kappa number is used to determine the delignification degree. The kappa number refers to the corrected permanganate test value for pulp corrected to 50% chemical consumption. The kappa number has the advantage of being linearly related to the lignin content over a wide range, for example kappa number × 0.15% =% lignin in the pulp.

  An additional aspect of the present invention relates to a method of treating a pulverized cellulosic fibrous material, wherein the cellulosic fibrous material is treated with a carbonate-containing solution to produce a pretreated cellulosic material. Treating the treated cellulosic material with a pulping chemical at a sufficient temperature for a sufficient amount of time to produce a liquid containing cellulose pulp and used pulping chemical, and a liquid containing used pulping chemical Is used to produce a carbonate-containing solution from the used pulping chemical, and the carbonate-containing solution produced from the used pulping chemical is used as the carbonate-containing solution in the above-mentioned method a).

  Another aspect of the present invention is a method for treating a pulverized cellulosic fibrous material, wherein a) the step of treating the cellulosic fibrous material with an acid solution, and b) the cellulosic fiber with a carbonate-containing solution. Treating the functional material to produce a pretreated cellulosic material, and c) treating the pretreated cellulosic material with sulfur-containing pulping chemicals for a sufficient time and at a sufficient temperature. Comprising a step of producing cellulose pulp, wherein the cellulosic fibrous material is treated with anthraquinone at least one of b) and c). Sulfur-containing pulping chemicals can typically contain sodium hydroxide and sodium sulfide.

  Yet another aspect of the present invention includes a pulp produced from one of the above-described methods having a higher yield than that produced from a prior art method. These and other aspects and advantages of the present invention can be more fully understood in light of the following description of the drawings.

  The invention will be better understood from the detailed description given below and from the accompanying drawings, which are merely illustrative and do not limit the invention.

1 is a schematic diagram illustrating a pulping process according to an embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a chemical recovery system that can be used in aspects of the present invention. FIG. FIG. 3 is a plot of the post-screen yield of pulp produced according to embodiments of the present invention compared to pulp produced by the prior art. FIG. 2 is a plot of light absorption coefficient values for pulp produced according to aspects of the present invention compared to pulp produced by the prior art. FIG. 3 is a schematic diagram illustrating the catalysis of the reaction of lignin and carbohydrates by anthraquinone, enhanced by aspects of the present invention.

  Applicants will symbolize a first pretreatment stage with a carbonate compound, such as sodium carbonate that is substantially free of sulfur, and a subsequent second pulping stage, such as anthraquinone (any anthraquinone symbolized). However, it has been found that improved pulp can be produced by treating ground cellulosic fibrous material such as wood chips in the soda pulping stage in the presence of AQ) . Improved pulp is also produced when the pulp is subjected to an acid treatment prior to the first pretreatment stage followed by kraft pulping in the presence of anthraquinone. For example, the pulp produced is characterized by better pulp yield, improved bleachability, higher strength, and lower defect rate, among other beneficial properties.

Furthermore, by treating the chips with a carbonate-containing solution before treating the chips with the pulping chemical, the amount of pulping chemical required in the pulping process for the desired treatment can be reduced. . This new fact can have a significant impact on attempts to reduce or eliminate the content of sulfur-containing pulping chemicals, most typically sodium sulfide (Na ₂ S). As mentioned above, non-sulfur pulping processes such as soda process and SAQ process have limited acceptance in the industry because the quality of the produced pulp is relatively poor compared to the sulfur retention kraft process. . In addition, soda and SAQ processes typically require a large amount of pulping chemical, sodium hydroxide (NaOH), compared to kraft processes. As discussed below, embodiments of the present invention overcome these limitations and produce an economically viable pulp.

An additional aspect of the invention relates to a method of treating a pulverized cellulosic fibrous material, wherein the cellulosic fibrous material is pretreated by treating with a carbonate-containing solution that is substantially free of sulfur. Cellulosic pulp and spent pulping chemicals by treating the pretreated cellulosic material with pulping chemicals such as alkaline pulping chemicals at a process, time and temperature sufficient to produce In the step of producing a liquid containing, a step of treating the liquid containing the used pulping chemical to produce a carbonate-containing solution from the used pulping chemical, and a) described in paragraph 16 above, It consists of the process of using the carbonate containing solution produced | generated from the used pulping chemical | medical agent as a carbonate containing solution. The carbonate-containing solution may contain sodium carbonate, including about 1% to about 12% sodium carbonate as Na ₂ O to the tip. The method may include an oxygen delignification treatment.

  In one aspect, treating the liquid containing spent pulping chemicals sufficiently concentrates the liquid to maintain combustion, burns the concentrate to produce a smelt containing carbonate, and , Introducing a liquid into the smelt and supplying a carbonate-containing solution from the used pulping chemical.

  Another aspect of the invention comprises a method of treating a pulverized cellulosic fibrous material, a) a step of treating the cellulosic fibrous material with an acid solution, b) a cellulosic solution with a carbonate-containing solution such as sodium carbonate. Treating the fibrous material to produce a pretreated cellulosic material; and c) treating the pretreated cellulosic material with a pulping chemical at a sufficient time and at a sufficient temperature. It consists of a step of producing cellulose pulp, and at least one of b) and c) is a treatment of the cellulosic fibrous material with anthraquinone.

  By using the processes and methods according to aspects of the present invention, some surprising results have been found from laboratory tests. These improvements include a greater reduction in factor H at the cooking stage than expected (the sum of factor H from the first stage treatment and factor H from the cooking is the same kappa number at the first stage carbonic acid. Less than factor H without salt treatment, as shown in Tables 2 and 3 below; increased pulp yield, increased bleaching, increased strength, and lower defect rate . As is known in the art and for the purposes of this application, Factor H refers to the method of expressing cooking time and temperature as a single variable for delignification.

  FIG. 1 is a schematic diagram of a pulping process 10 using aspects of the present invention, wherein a pulverized cellulosic fibrous material 12, such as wood chips, is treated in a carbonate pretreatment stage 14 and a cooking or pulping stage 16. Is done. Although the term “wood chips” is used to facilitate the discussion of the present invention, aspects of the present invention are not limited to chip processing, but hardwood chips, conifer chips, sawdust, recycled fibers, recycled paper May be used to treat any of the pulverized cellulosic fibrous materials, including but not limited to agricultural waste such as bagasse, and other fibrous cellulosic materials Those skilled in the art will appreciate.

  As is often seen in the art, before being introduced into the process 10, the chip 12 can generally be adjusted prior to processing, for example steaming to wet the chip, heating the chip, possible As much air and other gases can be removed to increase the penetration of the processing solution. The steam treatment of chip 12 may be performed prior to treatment, for example, by Andritz Inc., Glens Falls, NY. In a horizontal steam vessel or a Diamondback® steam vessel provided by According to an aspect of the present invention, in the carbonate stage 14 of the treatment (also referred to as c stage, pretreatment stage, or first stage), the chip 12 is a carbonate-containing solution 13, typically a sodium carbonate solution. Although treated, potassium carbonate and magnesium solutions may also be utilized. In one aspect of the present invention, the carbonate-containing solution can be substantially free of sulfur. This absence of sulfur does not mean that sulfur is not present in the carbonate solution in an absolute sense, but may mean that the solution is “substantially” free of sulfur. Those skilled in the art will appreciate. After processing in the first stage 14, the chip 12 is used in the second or pulping stage 16, i.e. in the cooking stage, with the pulping chemical 20 and sufficient time and sufficient temperature to produce the cellulose pulp 18. Then process. The pulp 18 is typically sent for further processing, among other conventional processes, such as for washing, bleaching, or screening. Carbonate-containing solutions 13 are available from a variety of sources, including commercially available carbonates and carbonates recovered from related processes, such as chemical recovery cycles (eg, illustrated and discussed below with respect to FIG. 2). However, it is not limited thereto.

According to an aspect of the present invention, the carbonate-containing solution 13 may have a concentration of carbonate (expressed as Na ₂ O) of about 1% to about 12% of wood. For example, the carbonate-containing solution may have a concentration of about 2% to about 9% as Na ₂ O versus wood. The carbonate-containing solution is typically provided as an aqueous solution, i.e., an aqueous solution of carbonate in water, although other compounds may be present. One skilled in the art understands the use of the term “about” when describing carbonate%, has difficulty in having an absolute measurement, and uses this term when describing carbonate%. Let's recognize that it can be seen everywhere. 1 kg mole of Na ₂ CO ₃ (106 kg) is equal to 1 kg mole of Na ₂ O (62 kg). Other carbonates such as potassium and magnesium may be added as Na ₂ O molar equivalents. The carbonate treatment 14 is typically performed at a temperature above 100 ° C., for example between about 120 ° C. and about 200 ° C. In one aspect, the carbonate treatment 14 may be performed between about 120 ° C and about 170 ° C, such as between about 120 ° C and about 150 ° C. One skilled in the art understands the use of the term “about” when describing a temperature range, has difficulty in having an absolute measurement, and uses the term “about” when describing temperature. Recognize that it can be found everywhere in the technical field. The use of the term “about” is used throughout this disclosure for any parameter of the treatment process, including pressure, time, temperature, percentage of components used in the pulping process, and other relevant measurements. It will be understood by those skilled in the art to define a measurement range for. At such temperatures, process 14 may typically be performed at an overpressure condition of about 50 psig to about 150 psig. The pretreatment stage 14 is typically performed for a time sufficient to provide at least some benefit to the pulp produced as a result of the process 10. For example, the pretreatment stage 14 may be performed for at least 5 minutes, but may be performed for about 15 minutes to about 6 hours depending on the nature of the feed material, i.e. the nature of the chip 12, but typically is about 15 minutes to about 120 minutes. Done minutes.

  In one aspect of the present invention, as indicated by 25, some of the liquid present in the chip can be removed or extracted from the chip 12 after the pretreatment 14 and prior to the pulping stage 16. In one aspect, the extracted carbonate-containing liquid 25 may be processed, disposed of, or otherwise reused, for example, in a recovery system. For example, in one aspect, a carbonate-containing liquid may be recycled and used as a source of carbonate 13 or as a supplement to carbonate 13.

After the pretreatment stage 14, the carbonate pretreatment chip 12 is treated in the pulping stage 16 using pulping chemicals for a sufficient time and at a sufficient temperature so that cellulose pulp 18 is produced. A single stage 16 is shown in FIG. 1, but according to one aspect of the invention, it may have one or more pulping stages 16. According to one aspect of the present invention, the pulping chemical 20 used in the pulping stage 16 can be primarily sodium hydroxide (NaOH), ie, the pulping stage 16 is a “soda” pulping stage. It can be. In another aspect of the invention, the pulping chemical 20 can include NaOH and sodium sulfide (Na ₂ S), ie, the pulping stage can be referred to as a “sulfate” or “kraft” process. If the pulping stage includes a kraft pulping stage, in one aspect, the acid stage 22 (discussed below) may be performed prior to the carbonate stage 13. However, according to an aspect of the present invention, the pulping of the pretreated chip 12 is performed in the pulping stage 16 in the presence of at least one anthraquinone (AQ).

In one embodiment, pulping of chip 12 in the presence of AQ is performed as described in US Pat. No. 6,569,289, the disclosure of which is incorporated by reference in its entirety. Can do. Applicants have found that the pre-treatment of chips 12 with carbonates, especially Na ₂ CO ₃ followed by SAQ pulping has improved properties compared to pulps obtained by prior art processing, eg improved It has been found that pulp 18 is obtained with yield, reduced lignin, and increased degree of bleaching. For example, experiments performed by the applicant have shown that carbonate or carbonate-AQ pretreatment and pulping processes of the present invention can typically produce synergies that cannot be predicted from prior art treatments with AQ. Suggests.

  According to an aspect of the invention, at least one AQ, or a derivative or equivalent thereof, is introduced into the pretreatment stage 14, the pulping stage 16, or both stages 14 and 16. In one aspect, AQ can be supplied in its reduced form (ie, a chemical commonly referred to as AHQ, see FIG. 5). In one aspect, an aqueous solution of AQ may be introduced into the carbonate pretreatment stage 14 (as shown by the dashed line 17 in FIG. 1), for example, before, at the beginning, in the middle, near the end, or Several combinations of these may be introduced. The concentration of aqueous AQ introduced during step 14 may range between about 0.01% to about 0.20% by weight on a chip basis, but is typically about 0.05 to about 0.10. Between weight percent. For purposes of this application, AQ can be added at any time during the pulping process shown in FIG.

  In one aspect, AQ may be introduced into the pulping stage 16 (as indicated by line 21 in FIG. 1), eg, at the beginning of this stage, in the middle, near the end, or some combination thereof. It's okay. The concentration of aqueous AQ introduced during the pulping stage 16 may range between about 0.01% to about 0.20% by weight with respect to the chip, but typically is about 0.00% with respect to the chip. Between 05 and about 0.1% by weight. In one aspect, AQ may be introduced at the carbonate stage 14 and removed from the pulping stage 16, and in another aspect, AQ may be introduced into both the carbonate stage 14 and the pulping stage 16.

According to an embodiment of the invention, after the first treatment stage 14 using a carbonate-containing solution, for example a sodium carbonate solution as a sulfur-free carbonate solution, NaOH (eg about 13% NaOH relative to wood). Surprising results have been confirmed in laboratory tests when performing the second pulping stage 16 using AQ (in input) and AQ (ie SAQ cooking stage). 13% NaOH dose versus timber corresponds to about 10% of Na ₂ O, i.e., NaOH of 2kg mole or 80kg is equal to Na ₂ O of 1kg mole or 62kg. For example, in laboratory tests, if the first carbonate stage 14 is followed by a second soda pulping stage 16 (using 13% NaOH for wood) in the presence of AQ, the pulping process is significant. Produced pulps with low NaOH requirements and yields close to that produced by kraft pulp without increasing the defect rate.

  In another aspect of the present invention, the chip 12 can be treated with the acidic solution 19 in the acid stage 22 before the pretreatment stage 14 (shown by the dashed line in FIG. 1). If kraft pulping in the presence of AQ is the pulping method used, carbonate treatment 14 may be performed after acid pretreatment 22. Although any acid-containing solution can be used as the acid 19, in one aspect, the acid 19 is a non-sulfur-containing acid solution, such as an organic acid (such as acetic acid) or an inorganic acid (such as nitric acid or hydrofluoric acid). preferable. In one embodiment, step 22 can be performed in the presence of a naturally occurring acid, i.e., in the presence of a naturally occurring wood vinegar. The acid solution 19 can be used to create an aqueous environment around the chip 12 having a pH of about 6 or less, such as a pH between about 4 and about 6. The acid treatment may be performed at a temperature higher than 50 ° C, for example from about 80 ° C to about 160 ° C. The acid treatment stage 22 is typically performed for a time sufficient to provide at least some benefit to the pulp produced by the process 10. For example, the acid treatment step 22 can be performed for at least 5 minutes, but may be performed for about 30 minutes to about 6 hours, and typically is performed for about 30 minutes to about 6 hours depending on the nature of the feed material, such as the pH of the chip 12. 90 minutes. The amount of acid required can be any amount required to exert the same effect as 2 to 6% acetic acid at 120 ° C.

  As shown in FIG. 1, in one aspect of the invention, before acid treatment 22 and before carbonate pretreatment 14, as shown by extraction stage 23 (shown in phantom in FIG. 1), acid After processing 22, at least a portion of the liquid present in the chip 12 may be removed or extracted. In one aspect, the extracted acid-containing liquid 23 may be processed, disposed of, or reused, for example, in a recovery system. For example, in one aspect, the acid-containing liquid can be recycled and reused as a source or supplement of acid 19.

  The acid treatment can be supplied from the chip 12, for example, the acid of stage 22 is obtained from mature wood (ie wood stored for a time sufficient to produce an acid liquid that naturally occurs from the wood itself). Acid can be used. In another aspect, the acid of step 22 may be supplied by a conventional acid hydrolysis process, for example, a process used to remove metals and other contaminants from the chip 12. One such process is disclosed in US Pat. No. 5,338,366, the disclosure of which is hereby incorporated by reference in its entirety.

In accordance with an embodiment of the present invention, the acid treatment stage 22 comprises the carbonate pretreatment stage 14, NaOH (soda) and AQ, or NaOH and Na ₂ S (kraft) and AQ, or soda and AQ and kraft and AQ. Combining with the pulping stage 16 having any of the combinations can reduce chemical consumption (eg, the amount of NaOH required) and increase the bleaching degree of the resulting pulp 18. That is, the amount of bleaching chemical required to achieve the desired whiteness can be reduced compared to prior art processing. In some aspects of the invention, it is also possible to see an improvement in pulp yield when using a process in which the acid treatment 22 is followed by the carbonate treatment 14 followed by SAQ. An improvement in the degree of bleaching is observed when the pulping stage 16 is a kraft process. The chemical consumption disadvantages of SAQ cooking can be addressed by the carbonate treatment stage 14, and embodiments of the present invention can also increase the bleaching degree of the pulp by oxygen and other one-electron transfer oxidants such as chlorine dioxide. Can be improved. The acid treatment stage 22 (A) can further improve the bleaching degree of both soda-AQ and kraft pulp, especially after the oxygen (O) delignification stage. Kraft green liquor (Na ₂ CO ₃ + Na ₂ S) can be used as a carbonate source 13 when the pulping process 16 includes a kraft process.

  FIG. 2 is a schematic diagram of a chemical recovery system 100 that can be used in aspects of the present invention. The chemical recovery system 100 contains sodium carbonate and sodium sulfide, among other black liquor combustion products known in the art (if the black liquor includes kraft black liquor) chemical smelt (not shown). A conventional recovery furnace or gasifier 110 for burning the concentrated spent cooking liquor 112, e.g., black liquor. According to conventional techniques, the carbonate-containing smelt dissolves in water in the container 114, ie, the green liquor tank, to produce an aqueous solution containing carbonate (known as “green liquor”). In one aspect, sulfide containing green liquor may be used in carbonate-containing solutions when the pulping stage includes kraft pulping. Prior to the carbonate treatment with green liquor, acid treatment (stage 22 in FIG. 1) is performed, followed by kraft pulping. Container 114 may be a green liquor tank or other suitable container known in the art. According to prior art techniques, the aqueous sodium carbonate in vessel 144 is typically advanced to further processing 120, ie causticization, thereby being used for cooking or bleaching, for example for oxygen delignification. The NaOH that will be regenerated. According to aspects of the present invention, the green liquor carbonate in container 114 can be used as one source of carbonate 13 for the pretreatment stage 14 shown in FIG.

  The improvements and advantages provided by the embodiments of the present invention have been investigated by the Applicant in a laboratory batch processing vessel, ie a laboratory batch steamer. The results of one such laboratory test are summarized in Table 1. Such containers are commonly used to develop processes for continuous and batch cookers. In the present invention, a continuous or batch steamer may be used.

  Table 1 summarizes the processing conditions and results obtained by a series of laboratory tests using a batch steamer. The present invention falls under Tests 1, 3, and 4 of Table 1, where at least some sodium carbonate is fed to the first processing stage and then fed to the soda-AQ (SAQ) pulping stage. Experiment number 2 is a reference test corresponding to a conventional SAQ pulping stage without carbonate pretreatment, and experiment number 5 is a reference test corresponding to a conventional kraft cooking without AQ.

In these laboratory tests, 0.8 kg sugar maple (Acer saccharum) chips (hardwood) were placed in the laboratory steamer. The carbonate pretreatment summarized in Table 1 uses a Na ₂ CO ₃ dose of 4.0 to 6.0% as chip Na ₂ O, ie 6.8 to 10.3% Na ₂ CO _3. At 165 ° C. and 170 ° C. In Experiments 1, 3, and 4, soda-AQ pulping was performed after carbonate pretreatment (CPC = carbonate pre-cooking) using only 10% NaOH dose as chip Na ₂ O. In the initial test method, after carbonate pretreatment, the batch cooker is depressurized (ie, “blowing the cooker”) to condense the carbonate stage off-gas (ie, effluent). NaOH and AQ were added to the condensate effluent, and the effluent with NaOH and AQ was charged again into the steamer containing the chip sample. The steamer was then heated to the pulping temperature as before.

  Table 1 includes “Factor H” for test pretreatment and cooking stages. As is known in the art, Factor H normalizes the rate of alkaline delignification with respect to processing temperature. Typically, the treatment becomes more severe as the factor H increases. The H factor during the second heating rise is entirely included in the SAQ cooking. Table 1 also provides the pH of the liquor in the steamer after carbonate pretreatment and after soda-AQ treatment.

  The advantages of the present invention are reflected in the “post-screen yield”, “failure rate”, and “kappa number” data shown in Table 1. As is known in the art, post-screening yields are determined after processing and for chips, fines, pins, etc. that have not been fully pulped in the process, and other non-fibrous debris. The percentage of the original chip present in the pulped chips after the pulp has been screened for removal. As is known in the art, higher relative post screen yields are preferred. The defect rate indicates how much of the original chip was not completely digested by a process such as isolation by screening. The lower the defect rate, the less wood that is discarded or reprocessed. As is also known in the art, the kappa number is a relative indication of the amount of undesirable lignin present in the resulting pulp. Typically, the higher the kappa number, the more lignin present in the pulp and the more bleaching chemicals are required to achieve the desired post-bleaching whiteness. Therefore, a lower kappa number is preferred.

The data in Table 1 confirms the advantages of the present invention. The data shown in Table 1 shows that the conventional soda-AQ pulping is dramatically improved by the method shown in FIG. For example, as shown in FIG. 1, the defect rate value most clearly shows the advantages of aspects of the present invention. According to Table 1, the experiment number 4 corresponding to carbonate pretreatment and soda-AQ pulping shows a value 0.3 for the defective rate and a post-screening yield of 55.3%. In comparison, run number 2, which represents the prior art SAQ pulping, shows a value for the failure rate of 27.0% and a significantly lower screen yield of 28.4%. This means that aspects of the present invention digest pulp more efficiently to produce pulp while retaining a significant portion of cellulose, as evidenced by high yields. . That is, the lower the defect rate, the more efficient the cooking process. Also, the data in Table 1 shows that in all four cases, experiment number 2 (corresponding to the prior art SAQ process) is performed in experiments 1, 3, even if the application of NaOH was 10% Na ₂ O for wood. 2 and 4 (representing embodiments of the present invention), resulting in a lower SAQ final pH. Applicants theorize that the lower pH of the prior art SAQ process is due to NaO, a stronger base that surpasses Na ₂ CO ₃ in the uneconomic carbohydrate degradation reaction. Na ₂ CO ₃ is not a strong enough base to remain in solution with SAQ cooking and cause the alkaline rearrangement necessary for lignin depolymerization and solubilization. If only Na ₂ CO ₃ is added in the pre-treatment, the reactive carbohydrate will react with it since this is the only alkali present. According to aspects of the present invention, more NaOH is added to stage 16 towards lignin depolymerization or degradation, thus providing a more effective pulping process.

In order to obtain a basis for comparison with embodiments of the present invention, cooking without carbonate pretreatment was also investigated in laboratory tests. The results of these tests are summarized in Table 2. In these tests, a series of kraft and SAQ pulps were prepared from sugar maple chips without carbonate pre-cooking. One of the kraft pulping tests was conducted with a higher degree of sulfidation and lower effective alkali (NaOH to chip 10% Na ₂ O and Na ₂ S to chip 5% Na ₂ O). See the second row of data. This kraft pulping test (second row of Table 2) results in a higher post-screen yield (about 1.0% higher post-screen yield on chip) compared to the kraft test with higher EA, ie Vs. chip 12% Na ₂ O from NaOH and 4% Na ₂ O vs. chip from Na ₂ S (see first row of data in Table 2). Both pulps had approximately the same unbleached kappa number (ie 17.4 and 17.8). However, as discussed below, pulp produced using lower EA (ie, 10% NaOH and 5% Na ₂ S, second row of Table 2) has higher EA (12% NaOH and It appeared to be less responsive to oxygen (O ₂ ) delignification than the pulp produced to have 4% Na ₂ S). The Applicant understands that the difference in post O ₂ Kappa number between these pulps is significant. A series of SAQ tests were also conducted, as also shown in Table 2. As shown, tests with various EA and AQ charges of 0.1% versus chip produced pulps with a relatively low defect rate and a low kappa number of 15.2.

The carbonate pre-cooking according to one embodiment of the present invention was investigated in a laboratory test. The results of these tests are summarized in Table 3. Table 3 provides treatment conditions for SAQ treatment (Experiments 1-5) and Kraft treatment (Experiments 6 and 7) after pretreatment of the chips with carbonate. The advantages of carbonate pre-cooking according to embodiments of the present invention are apparent by comparing the results shown in Table 2 (prior art) with the results shown in Table 3. For example, comparing Experiment 1 in Table 3 with the conventional SAQ in Table 2 (Table 5, line 5), a 30 minute carbonate stage at 165 ° C. (“C ₁ condition”, footnotes 2 and 3 in Table 3). It can be seen that the alkali requirement at the SAQ stage has decreased from 14.0% (in Table 2) to 10% (in Table 3) as Na ₂ O. In comparison of the produced kappa number, unbleached pulp produced with carbonate pretreatment slightly reduced its kappa number (18.4 vs. 19.3), while resulting in carbonate pretreatment A slightly higher post-screening yield is shown (53.1% vs. 52.8%). Comparison of carbonate-SAQ according to aspects of the present invention (eg, Experiment 5 in Table 3) with carbonate-kraft (eg, Experiment 7 in Table 3) relates to carbonate-SAQ compared to carbonate-kraft treatment. It can be seen that a higher yield (vs. 1.0% of chip) can be obtained. Higher yields result in a more efficient process and therefore a high post-screen yield is desired.

Aspects of the invention may result in a reduction in factor H at the cooking stage that is greater than expected. Comparing the results shown in Table 2 with the results shown in Table 3, Factor H obtained in the treatment performed without carbonate pretreatment showed that for the same kappa number, the total H for carbonate pretreatment and cooking Clearly higher than the factor. For example, Factor H of the untreated pulp (lines 3-5 of Table 2) was over 1600 for SAQ. SAQ Stage H Factor (Experiments 1-2 in Table 3) for the first two carbonate (C ₁ ) pretreated pulps is 1239, C ₁ Stage H Factor 358 is a total for the combination of carbonate and SAQ treatment 1597. The resulting carbonate pretreated pulp (1st row of Table 3) with a kappa number of 18.4 has improved post-screening yield, improved bleaching degree and is not pretreated It resulted in a lower defect rate than pulp. A further comparison showing the advantages of aspects of the present invention can be found in FIG. 3 as discussed below.

After the cooking test discussed above and summarized in Tables 2 and 3, the cellulosic material was bleached. The bleaching sequence used in the laboratory test was OD ₀ EpD ₁ (O is the alkaline O ₂ stage; D ₀ is chlorine dioxide delignification with a final pH of 2-3; Ep is gradual delignification. alkaline extraction with sodium hydroxide and hydrogen peroxide for; _{D 1,} the final pH of the chlorine dioxide brightening of 3.4 to 4.5). D application of chlorine dioxide at ₀ stage, wherein: based on the kappa number of the weight% = 0.076 × O ₂ pulp pulp chlorine dioxide. According to laboratory tests performed, Applicants have found that 21.5 kappa pulp produced in the soda-AQ pulp test (ie, data in row 4 of Table 2) is 12.5% Na ₂ This pulp can be bleached more than the pulp produced when using 14.0% Na ₂ O (ie, data in lines 5 and 6 of Table 2). I found it difficult. The decrease in kappa number due to O ₂ is typically a measure of the ease of bleaching. According to an aspect of the invention, the bleaching degree of soda-AQ pulp is improved by carbonate pretreatment. Although this particular bleaching sequence was used in the study of the present invention, according to embodiments of the present invention, any suitable known bleaching process can be used, including a bleaching process that removes chlorinated compounds, i.e. One skilled in the art will appreciate that it includes a complete chlorine-free (TCF) bleaching process in which chlorine atoms are excluded, ie, a chlorine atom-free (ECF) bleaching process.

FIG. 3 shows a plot comparing screen yield as a function of kappa number after oxygen delignification, according to embodiments of the present invention, with the prior art. As illustrated, aspects of the present invention provide pulp that is more easily bleached than prior art methods. As is known in the art, the screen yield% is the weight of pulp produced from the process after screening the produced pulp to remove knots, fragments, and other undesirable materials. Of the wood to the weight of the process. A higher screen yield is preferred. The O ₂ kappa number is related to the lignin content of the digested and oxygen delignified pulp. A lower kappa number is preferred as is known in the art. 3 and 4, the following notation is used: A = acid; C = carbonate pretreatment; Kr = kraft treatment; SAQ = soda anthraquinone treatment. Message "(M + N)" is, M% NaOH against wood as Na ₂ O, and with Na ₂ O as a counter wood N% Na ₂ S, which means that processing has been performed. The method of the present invention further includes an oxygen delignification treatment, thereby having a lower kappa number after the oxygen delignification treatment at a predetermined post-screen yield compared to pulp produced by a method that does not perform the pretreatment stage 14. Produce pulp.

As shown in FIG. 3, there is a dramatic improvement in soda-AQ (“X” C-SAQ) with carbonate pretreatment compared to untreated soda-AQ pulp (“▲” SAQ). Is seen. According to the results of FIG. 3, the kappa number obtained by carbonate pretreatment and subsequent soda AQ (“X” C-SAQ) cooking shows the soda-AQ pulp (“▲” SAQ) kappa without pretreatment. A kappa number after O ₂ bleaching, which is lower than the value, is realized. For example, the O ₂ kappa number of C-SAQ (“X”) is just over 8 kappa when the post-screen yield is over 52%, and the O ₂ kappa number of SAQ (“▲”) is About 10.5 kappa with an equivalent post-screening yield of about 52.5%. That is, at an equivalent post-screening yield, embodiments of the present invention exhibit a lower kappa number compared to the prior art. Thus, carbonate treatment reduces the kappa number (both after unbleaching and after the O stage).

  In these laboratory tests, the yield loss in all oxygen stages was about 1.4-1.8% versus pulp. The small difference in yield loss during the O stage becomes insignificant when converted to a “vs. chip” basis. When carbonate treatment or acid treatment was followed by carbonate pretreatment (ie, “AC pretreatment”), the fiber yield of kraft pulping was not improved. However, as shown in FIG. 3, carbonate and acid + carbonate pretreatment (“X” C-SAQ and “*” AC-SAQ) reveals the yield of SAQ pulping (“▲”). Improved. That is, according to aspects of the present invention, a higher post-screening yield is provided compared to conventional SAQ pulping processes.

FIG. 4 shows a plot comparing fully bleached pulp as a function of post oxygen delignification kappa number with the prior art according to the present invention. The vertical axis in FIG. 4 is the light absorption coefficient (LAC) value of the completely bleached pulp after OD ₀ EpD ₁ bleaching, and the horizontal axis is the post-O ₂ kappa number. Examination of FIG. 4 reveals that conventional soda-AQ pulp (“「 ”) contains more color (ie, has a higher LAC value) than kraft pulp (“ ♦ ”). However, the soda-AQ pulp after acid (A) and carbonate (C) pretreatment (“Δ” and “◇”), according to aspects of the present invention, is equal to or greater than kraft pulp without pretreatment. It had a slightly lower color content.

  Additional laboratory tests were conducted to compare the properties of bleached kraft, bleached acid carbonate kraft, and bleached acid carbonate soda anthraquinone pulp. Some properties of prior art bleached kraft pulp, acid carbonate (AC) -kraft pulp according to aspects of the present invention, and acid carbonate (AC) -SAQ pulp according to aspects of the present invention from sugar maple chips, It is described in Table 4. As shown in Table 4, soda AQ pulp pretreated by both acid and carbonate treatment resulted in improved yields. The screen yield was highest for AC-SAQ, with a value of 53.2, compared to yields lower than 52 for both prior art kraft and AC kraft pulp. AC pretreatment increased the final whiteness of the kraft pulp from 91.0 to 92.6.

  As shown in FIG. 1, when digested according to embodiments of the present invention, at least a portion of the Stage A (acid stage) effluent, for example, 50% to 75% of the entire Stage A effluent is taken up in the carbonate-containing solution. Replace. In one aspect, at least a portion and possibly all of the carbonate stage effluent may be transferred to the craft or SAQ stage along with the chips. In the laboratory tests reported so far, the carbonate stage effluent was collected after passing through the condenser. NaOH was introduced into the effluent as pellets and the AQ powder was dissolved in the condensed effluent. The carbonate and AQ containing effluent was then returned to the laboratory steamer for the SAQ stage. In the case of kraft pulping, sodium sulfide solution and NaOH pellets were added to the carbonate stage effluent. In the present application, the whiteness is errefo%.

  Applicants speculate that the use of some or all of the carbonate stage effluent can be important for aspects of the invention, for example, the carbonate SAQ process. The applicant believes that the reason is probably that the carbonate effluent may contain many low molecular weight carbohydrates having reducing end groups. The dissolution of carbohydrate during the carbonate stage is estimated to be about 5% of the original chip mass (on oven dry basis). Applicants believe that random hydrolysis of carbohydrates is expected, and the formation of new reducing end groups can occur with each hydrolysis. A higher concentration of reducing end groups is believed to reduce AQ at a faster rate to form AHQ (anthrahydroquinone), an active delignin catalyst. The AQ / AHQ catalytic cycle is shown schematically in FIG. Further, when the reducing end group in the solid phase is oxidized to a carboxylic acid, an alkaline peeling reaction that reduces the molecular weight of the carbohydrate and lowers the pulp yield becomes difficult to occur. The above hypothesis can explain why the carbonate stage improves the pulp yield of SAQ pulping and does not improve the yield of kraft pulping. Oxidation of reducing end groups to carboxylic acids is not known to be (or even occurs) a significant reaction in the Kraft process or a soda process without AQ addition.

To further support the advantages of embodiments of the present invention, further laboratory studies were conducted on chips obtained from mixed wood. For example, a chip mixture containing about 60% of poplar deltoids clones, about 20% of birch (Petula papylifera), and about 20% of sugar maple was used. The results for prior art kraft pulping, prior art soda-AQ pulping, and pulping according to aspects of the present invention, ie, with acid and acid / carbonate pretreatments, are shown in Table 5. The acid pretreatment conditions are as follows.
A _1: vs. 20 min at 0.99 ° C. using a chip of 1.5% acetic acid (final pH about 3.5), and A _2: 3.0 percent at 120 ° C. with acetic acid (final pH 3.2) 60 minutes,
Met.

As shown in Table 5, _{A 1} pretreatment, bleached (i.e., "last") but whiteness produced a high soda -AQ pulp (90.8) than Kraft (89.9), the pulp yield The rate was somewhat low. Milder, _{A 2} before treatment with acid carbonate -SAQ showed higher pulp yield (54.2%) than both conventional kraft pulping and SAQ pulping. The _A 2 C-SAQ treatment, bleached whiteness is higher than SAQ pulping (88.4) resulted in lower values (89.2) than kraft pulping (89.9). In one aspect of the invention, Applicants believe that the severity of the acid (A) stage is higher for this chip feed than A ₂ acid treatment, but lower than A ₁ acid treatment. . Also, as shown in Table 5, the rate at which tensile strength appears after purification of 2000 PFI rotation is shown by the “tensile index”, acid kraft pulping (78.3) and acid-SAQ pulping (86. 1) was lower than kraft pulping (94.4). However, acid-carbonate-SAQ has the highest rate (ie, 100.2), further highlighting the advantages of embodiments of the present invention. From the results shown in Table 5, it appears that the pulp with higher yield and possibly more hemicellulose requires less refining. There was no significant difference in the tensile-tear curves.

Furthermore, in order to fully understand the advantages of carbonate-SAQ pulping and to clarify the difference between the present invention and the previous work of the '241 patent without anthraquinone, milder carbonate stage conditions Studied. The results of this survey are summarized in Table 6. A chip feed consisting of 50% sugar maple, 40% cotton willow, and 10% birch was prepared. The carbonate treatment step according to an embodiment of the invention is carried out at 130 or 140 ° C. for 30 or 60 minutes with 3.0 or 5.0% Na ₂ CO _{3 charge} (as Na ₂ O) versus wood It was. In these tests, it took about 30-35 minutes to reach the maximum temperature. About 70% of the carbonate stage effluent was discharged and discarded after the carbonate treatment. The carbonate effluent was replaced with distilled water when the pulping chemical was added to SAQ or kraft cooking.

According to the results shown in Table 6, in the carbonate-SAQ treatment with a carbonate stage with 3% vs. chip Na ₂ CO ₃ (as Na ₂ O) and a required time of 60 minutes at 140 ° C. (See, for example, Experiment 5). The pulp obtained from Experiment 5 has a yield after chip screen of about 2.0% higher than Experiment 8 (standard kraft cooking), and the loss after oxygen delignification is 1.7 kappa compared to Experiment 8. It was only a unit. When compared with pretreated kraft pulp (Experiment 6), the yield of carbonate-SAQ pulp (Experiment 5) was about 1.0% better than chips. This good yield is believed to correspond to a net increase in profit of about $ 4M per year in a typical chemical pulp mill.

  Furthermore, the factor H combined in the carbonate (C) and soda-AQ stages in Experiment 5 is 897 (81 + 816) and the pulp produced with the prior art SAQ without pretreatment but with factor H 992 Approximately the same kappa number (23.1 vs. 22.6), higher yield (55.8 vs. 54.2), and lower defect rate (0.6 vs. 1.0) compared to (Experiment 9) A pulp with was produced. The time spent in the carbonate stage is believed to have a significant effect on the resulting pulp. In the laboratory test, the carbonate stage was carried out for an additional 30 minutes at pH of about 8 (see Experiment 4 vs. Experiment 5), which resulted in 1.6 kappa units better after soda-AQ and oxygen delignification. Higher post-screening yields were obtained by extending the carbonate stage for an additional 30 minutes. In addition, spending 30 minutes of this extension in the carbonate stage produces more reducing end groups, and by increasing the total cooking time, more defective rates are converted to screened fibers. It is thought.

  Aspects of the present invention include batch (including, but not limited to, conventional SuperBatch® and Rapid Displacement Heating) or continuous (conventional soda, conventional craft, Lo-Solids ( (Registered trademark) Cooking, EMCC (registered trademark) Cooking, ITC (registered trademark) Cooking, and Compact Cooking, and the like. Can be performed in equipment used in any or all of the acid, carbonate, and cooking stages. Aspects of the invention may be used during transportation or storage of pulverized fibrous material, for example, as described in US Pat. No. 6,55,462, the disclosure of which is incorporated herein by reference. Pre-processing can also be performed. In a batch system, the liquid in the steamer can be transferred using conventional means such as pumping the liquid into a container, or the liquid can be transferred to the steamer according to the original pressure of the liquid or pumping means. The fresh cooking liquor can then be added to the cooking kettle. All liquids, such as liquid extracted from SuperBatch or RDH methods, can be preheated using methods known in the art. Furthermore, heating of the liquid can be achieved in the vessel by a circulation loop or direct steam addition.

  The aspects of the present invention described herein provide a pulping process that provides a beneficial improvement over the cellulosic material pretreatment process and prior art treatment of wood chips and related ground materials. And provide. As is evident from the test data presented herein, pretreatment of wood chips with carbonate solution in the presence or absence of anthraquinone results in higher yields, lower defect rates, and greater strength. Cellulose pulp can be produced and less chemicals can be produced and bleached.

  Although several aspects of the invention have been described and illustrated herein, alternative aspects may be shown by one skilled in the art to accomplish the same purpose. Accordingly, the appended claims are intended to cover all alternative embodiments within the true spirit and scope of this invention.

Claims (48)

A method for treating a pulverized cellulosic fibrous material comprising:
a) treating the cellulosic fibrous material with a carbonate-free solution containing no sulfur to produce a pretreated cellulosic material;
b) consisting of treating the pretreated cellulosic material with pulping chemicals for a time and at a temperature sufficient to produce cellulose pulp, at least in one of a) and b) A method in which the cellulosic fibrous material is treated with anthraquinone.   The method of claim 1, wherein the cellulosic fibrous material is treated with anthraquinone in a).   The method according to claim 1 or 2, wherein the pretreated cellulosic fibrous material is treated with anthraquinone in b).   4. The method according to claim 1, wherein the carbonate-containing solution comprises a sodium carbonate-containing solution. The method according to any one of claims 1 to 4, wherein the carbonate-containing solution comprises an aqueous solution having a carbonate concentration of 1% to 12% as Na ₂ O with respect to wood. The concentration method of claim 5, wherein the 9% 3% against the wood as Na 2 _O.   The method of claim 1, wherein the sulfur-free carbonate-containing solution comprises a sulfur-free sodium carbonate solution.   The method according to any one of claims 1 to 7, wherein the pulping chemical comprises sodium hydroxide.   9. The method according to claim 1, wherein the pulping chemical is sodium hydroxide.   The method according to any one of claims 1 to 9, further comprising the step of c) treating the pulverized fibrous material with an acidic solution before a).   11. The method according to claim 1, further comprising the step of: d) extracting at least part of the acidic solution from the cellulose fibrous material after c) and before a). the method of. The sodium carbonate solution, The method of claim 4, wherein the of 12% sodium carbonate 1% on chips as Na 2 _O. The sodium carbonate The method of claim 12, wherein the consisting of sodium carbonate between 2% and 7% on chips as Na 2 _O.   The method according to any one of claims 1 to 13, wherein a) is performed at a temperature higher than 100 ° C.   The method according to any one of claims 1 to 14, wherein a) is performed at a temperature between 120 ° C and 170 ° C.   The method according to any one of claims 1 to 15, wherein a) is performed at a temperature between 120 ° C and 150 ° C.   The method according to any one of claims 1 to 16, wherein a) is performed for 15 minutes to 120 minutes.   The method according to any one of claims 1 to 17, wherein a pulp having a low defect rate and a high post-screening yield is produced as compared with a pulp produced by a method not performing a).   The method according to claim 1, wherein the method is performed continuously.   Furthermore, it contains oxygen delignification treatment, and produces a pulp having a low kappa number after oxygen delignification treatment in a predetermined post-screening yield as compared to pulp produced by a method not performing a). 20. A method according to any of claims 1 to 19, characterized in that   21. A method according to any one of the preceding claims, wherein the treatment with anthraquinone consists of a water-soluble anthraquinone having a concentration between 0.01% and 0.20% by weight with respect to the chip.   The treatment with anthraquinone comprises water-soluble anthraquinone having a concentration between about 0.05% and about 0.10% by weight on a chip basis. Method.   The said anthraquinone is introduced after a), and consists of an anthraquinone aqueous solution with the density | concentration of 0.01 weight%-0.20 weight% with respect to a chip | tip. Method. Treating the pretreated cellulosic material with the pulping chemical further comprises producing a liquid containing the used pulping chemical;
Processing a liquid containing the used pulping chemical to produce a carbonate-containing solution from the used pulping chemical; and
The method according to any one of claims 1 to 23, comprising a step of using a carbonate-containing solution produced from a used pulping chemical as the carbonate-containing solution in a). Treatment of the liquid containing the used pulping chemical,
Concentrating the liquid enough to maintain combustion;
Burning the concentrate to produce a carbonate-containing smelt; and
25. The method of claim 24, comprising introducing a liquid into the smelt and supplying a carbonate-containing solution from the used pulping chemical. The carbonate-containing solution, according to claim 24 or 25 method wherein a consisting of sodium carbonate between 2% and 7% on chips as Na 2 _O.   27. A process according to any of claims 1 to 26, wherein the pulp has a higher yield than the pulp produced according to the prior art. Furthermore, those containing an oxygen delignification and at least one bleaching stage, according to any one of claims 1 to 26, characterized in that to produce a cellulosic pulp having a high whiteness than 88% Erurefo Method. A method for treating a pulverized 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 sulfur-containing pulping chemical for a sufficient time and at a sufficient temperature to produce a cellulose pulp;
A method wherein the cellulosic fibrous material is treated with anthraquinone at least one of b) and c).   30. The method of claim 29, wherein the cellulosic fibrous material is treated with anthraquinone in b).   31. A method according to claim 29 or 30, wherein the pretreated cellulosic fibrous material is treated with anthraquinone in c).   32. The method according to claim 29, wherein the carbonate-containing solution comprises a sodium carbonate-containing solution.   33. A method according to any of claims 29 to 32, wherein the sodium carbonate containing solution comprises kraft green liquor. The method according to any one of claims 29 to 33 wherein the carbonate-containing solution, characterized in that it consists of an aqueous solution having a concentration of from 1% Na 2 _O against wood 12% carbonate. The method according to any one of claims 29 to 34 wherein the carbonate-containing solution, characterized in that it consists of an aqueous solution having a concentration of from 3% Na 2 _O against wood 9% carbonate.   36. The method according to any one of claims 29 to 35, further comprising: d) extracting at least part of the acidic solution from the cellulosic fibrous material after a) and before b). The method described in 1.   37. A method according to any of claims 29 to 36, wherein b) is performed at a temperature higher than 100 <0> C.   38. A method according to any of claims 29 to 37, wherein b) is performed at a temperature between 120 <0> C and 170 <0> C.   40. A method according to any of claims 29 to 39, wherein b) is performed at a temperature between 120 <0> C and 150 <0> C.   41. A method according to any of claims 29 to 40, wherein b) is performed for 15 minutes to 120 minutes.   41. A method according to any of claims 29 to 40, characterized in that it produces a pulp having a low defect rate and a high post-screening yield as compared to pulp produced by a method which does not carry out b).   42. A method according to any of claims 29 to 41, wherein the method is carried out continuously.   Furthermore, it contains oxygen delignification treatment and produces a pulp having a low kappa value after oxygen delignification treatment in a predetermined post screen yield compared to pulp produced by the method not performing b). 43. A method according to any of claims 29 to 42.   44. A method according to any of claims 29 to 43, wherein the treatment with anthraquinone comprises a concentration between 0.01% and 0.20% by weight on a chip basis.   45. A method according to any of claims 29 to 44, characterized in that the treatment with anthraquinone comprises a concentration between 0.05 and 0.10 wt% on a chip basis.   46. Any of the claims 29 to 45, characterized in that the anthraquinone is introduced after b) and the treatment with anthraquinone has a concentration between 0.01% and 0.20% by weight on a chip basis. The method described. The step of treating the pretreated cellulosic material with a sulfur-containing pulping chemical further comprises the step of producing a liquid containing a used pulping chemical,
Treating the liquid containing the used pulping chemical to produce a carbonate-containing solution from the used pulping chemical; and
47. The method according to any one of claims 29 to 46, comprising a step of using a carbonate-containing solution produced from a used pulping chemical as the carbonate-containing solution in b). Treatment of the liquid containing the used pulping chemical,
Concentrating the liquid enough to maintain combustion;
Burning the concentrate to produce a carbonate-containing smelt; and
48. The method of claim 47, comprising introducing a liquid into the smelt and supplying a carbonate-containing solution from the used pulping chemical.

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