RU2445414C2 - Methods of carbonate pretreatment and pulping cellulosic material - Google Patents

Abstract

FIELD: textiles, paper.

SUBSTANCE: at the stage a) processing of cellulosic fibrous material is carried out with sulfur-free carbonate solution to obtain pre-treated cellulosic material, and at the end of a) with the solution having a ph of 7 to 9.1. At stage b) processing of pretreated cellulosic material is carried out with pulping chemical for a sufficient time and at a sufficient temperature to obtain a cellulosic pulp. Moreover, at least at one stage the cellulosic fibrous material is processed with anthraquinone.

EFFECT: method enables to reduce the amount of pulping chemical spent for pulping process during the required treatment.

50 cl, 5 dwg, 6 tbl

Description

Description

FIELD OF THE INVENTION

The present invention relates to a method for the technological processing of pulverized cellulosic fibrous material, for example wood chips, by carbonate pretreatment before starting to cook the cellulosic material with the cooking chemical in the presence of anthraquinone (AQ).

BACKGROUND OF THE INVENTION

In the field of chemical cooking technology, cellulosic material, such as wood chips, is processed by cooking chemicals to produce cellulose for use in the manufacture of paper and other products. The use of caustic soda (which is sodium hydroxide [NaOH] as a cooking chemical), called soda cooking, in boilers for both batch and continuous pulping is well known in the art. There are many advantages of soda boiling, including the possibility of increasing the design pressure of the recovery boiler to increase its productivity and to eliminate the presence of sulfur in the process. Among other beneficial effects, eliminating the presence of sulfur during cooking allows the use of black liquor in gasification systems. The use of gasification black liquor results in an increase in production capacity, which is many times higher than the production capacity based on the use of a sulfur-containing system.

One of the drawbacks of soda cooking is the low yield of cellulose (both for softwood and hardwood), compared with the yield achieved using kraft cooking, which is cooking using sodium hydroxide (NaOH) and sodium sulfide (Na ₂ S) as cooking chemicals. However, the addition of anthraquinone (AQ) to soda cooking has been shown to increase the yield of cellulose and thus make the yield of cellulose comparable to that of kraft cooking. However, even with the addition of AQ, the pulp after the soda cooking process is characterized by weaker strength properties and insufficient whiteness compared to kraft cooking.

However, disadvantages are also inherent for soda anthraquinone (SAQ) cooking compared to kraft cooking. As an example, SAQ cooking requires higher amounts of NaOH and it is much more difficult to bleach the pulp obtained from the SAQ cooking process. For example, more NaOH is spent, more recustification is required. As is known from the technical field, during recaustification with sodium carbonate for the regeneration of NaOH, processes proceed as indicated in equations 1 and 2 below:

Na ₂ CO ₃ + CaO + H ₂ O → 2NaOH + CaCO ₃ [1]

CaCO ₃ → CaO + CO ₂ [2]

The volume of NaOH spent per ton of wood to produce pulp is greater in the case of SAQ cooking compared to the volume of NaOH spent for kraft cooking. This larger amount of NaOH spent in SAQ cooking is necessary to compensate for the sodium sulfide present in kraft cooking that is not present in SAQ cooking. As is known in the art, the sodium sulfide (Na ₂ S) present in kraft cooking is hydrolyzed to NaSH and NaOH, and thus affects the pulping of the cellulosic material during the course of the kraft cooking. The amount of NaOH spent in AQ soda cooking is approximately 20% to 40% more than in kraft cooking. The higher consumption of NaOH as a result leads to higher energy costs for the conversion, or causticization, of sodium carbonate (Na ₂ CO ₃ ) from the recovery boiler to NaOH used in the autoclave, and in other parts of the fiber production line.

As an example, when active alkali (AA = NaOH + Na ₂ S, based on Na ₂ O) with 16.0% Na ₂ O and 30% sulfide, is used for kraft pulping, 11.2% AA comes from NaOH and 4.8% AA comes from Na ₂ S. In regeneration during kraft cooking, when all sulfur is regenerated as Na ₂ S, recaustification will be required for conversion to NaOH in order to provide the specified 11.2% Na ₂ O for new wood chips. SAQ hardwood cooking requires approximately the same effective amount of alkali (EA = NaOH + ½ Na ₂ S, based on Na ₂ O), as well as kraft pulping. In the above example of Kraft pulping, EA was 13.6% Na ₂ O, and the same amount of alkali is required for SAQ pulping, but all of it usually comes in the form of NaOH.

In addition, it is well known that hemicelluloses quickly dissolve in soda, kraft and SAQ cooking, and that a significant portion of the NaOH used is spent on the degradation of hemicelluloses to products with low molecular weight (MW). These low molecular weight MW organic substances are difficult to recover from the cooking stream 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 soda recovery unit is predominantly Na ₂ CO ₃ when using the SAQ process.

It has been shown that cellulose from hardwood materials processed using the cooking methods of Lo-Solids® Cooking methods (as described in US Pat. 6,280,568; 6,346,167, which are incorporated by reference in their entirety) and Soda-AQ (SAQ) as cooking chemicals, result in cellulose with better strength properties compared to cellulose obtained by conventional kraft cooking. In addition, cellulose obtained from hardwood materials processed using the Lo-Solids® Cooking method with soda-AQ as a cooking chemical can be obtained with a better final brightness than conventional soda-AQ, but not light as kraft pulp. Despite the fact that the consumption of the bleaching chemical during Lo-Solids soda-AQ cooking is greater than with conventional soda-AQ cooking, to achieve a final degree of whiteness, cellulose still needs more bleaching chemicals than cellulose obtained by kraft cooking.

For this and other reasons, kraft cooking (and its many sulfur-related problems) is a widespread cooking process in industry. However, applicants have found that by pretreating the cellulosic material with a substantially sulfur free (<1 g / L total sulfur content) carbonate solution and then performing SAQ, the disadvantages of SAQ cooking can be overcome.

US Pat. No. 1,887,241 (incorporated by reference in its entirety) discusses pretreatment, also defining it as pretreatment of cellulosic material with sodium carbonate, followed by treatment of the resulting material with either soda boiling or kraft boiling. In the process disclosed in '241 petente, wood chips that are steam-treated can undergo such a carbonate pretreatment step at a temperature of approximately 330 degrees Fahrenheit, which is approximately 165 degrees Celsius (C). According to the '241 patent, a pre-treatment step using sodium carbonate reduces the amount of NaOH required. By way of example, as disclosed in US Pat. No. 1,887,241, the amount of sodium carbonate used is 10% of the amount of wood, together with 15% NaOH, compared to about 25% NaOH added in conventional soda cooking. Although pretreatment with sodium carbonate at approximately 165 degrees C is disclosed in the above patent, the high temperature treatment disclosed in the '241 patent (published in 1932), for various reasons, has not become widespread in the pulp and paper industry, and it is usually in practice at present not used. The treatment disclosed in the '241 patent also does not include the use of anthraquinone at any stage of the processing.

Recent advances in the pulp and paper industry include methods for removing silica from cellulosic material by using a solution containing sodium carbonate. (See US Application No. 2006/0225852, incorporated herein by reference in its entirety). The methods disclosed in 0225852 application, associated with almost 100% removal of silicon oxide contained in the cellulosic material, such removal is carried out before processing the fibrous material using conventional methods.

Aspects of the present invention provide a method for the technological processing of cellulosic material that overcomes the disadvantages and errors of the methods of the current state of the art. For example, some aspects of the present invention provide an approach to minimize or eliminate the presence of sulfur in a pulp mill, while at the same time producing a commercially competitive product — long-lasting but not yet met by the pulp industry.

SUMMARY OF THE INVENTION

The present invention, in its many aspects, relates to the pretreatment of cellulosic material with a carbonate solution, such as essentially sulfur free (<1 g / l total sulfur content) sodium carbonate (Na ₂ CO ₃ ), followed by cooking the pretreated cellulosic material in the presence of a cooking chemical, such as only a single sodium hydroxide (which is a “soda” process), but also sodium hydroxide and sodium sulfide (which is a “craft” process), or a combination of soda and cr aft processes, and in addition, at least with some kind of anthraquinone, i.e. anthraquinone or substituted anthraquinone, such as 2-methylanthraquinone. AQ can be added at any time during the process. As an example, AQ can be added at the pre-treatment stage, at the cooking stage, or even at the pre-processing stage, and at the cooking stage, both before and after each stage. (Addition of AQ in the cooking step may be carried out as described in US Pat. No. 6,569,289, incorporated herein by reference in its entirety).

One aspect of the invention is a method for treating pulverized cellulosic fibrous material in accordance with: a) treating the fibrous cellulosic material with a carbonate-containing solution, such as a substantially sulfur-free carbonate-containing solution, to obtain a pre-treated cellulosic material; b) treating the pre-treated cellulosic material with a cooking chemical for a sufficient time and at a sufficient temperature to obtain a pulp for which, in at least one of a) and b), the cellulosic fibrous material is treated with at least some anthraquinone. In this method, the cellulosic fibrous material can be treated with anthraquinone in steps a), b), or as in a) and b). In one aspect, the carbonate-containing solution may include a solution containing sodium carbonate. In another aspect, the cooking chemical may include sodium hydroxide. Moreover, the active cooking chemical may consist mainly of sodium hydroxide.

One aspect of the above process involves additional steps before step a), the pulped fibrous material can be c) treated with an acid solution, and after c), d) at least some acid solution can be recovered from the cellulosic fibrous material.

In another aspect, the method allows to obtain a pulp having a low percentage of rejected waste and a high percentage yield of sorted pulp, in comparison with the pulp produced without the practical implementation of stage a).

One aspect of the invention may further include an oxygen delignification type treatment, as well as at least one bleaching step, wherein the method provides a pulp having a whiteness of more than 88% (Elrepho). When an oxygen delignification type treatment is provided, the method allows the production of cellulose having a low permanganate number after the oxygen delignification type treatment with a predetermined yield of sorted cellulose compared to cellulose obtained without practical implementation a). As is known in the art, permanganate number is used to characterize the degree of delignification. It refers to the effective permanganate sample for technical pulp, which is adjusted for a 50% chemical consumption. The permanganate number has a predominantly linear relationship with the lignin content in a wide range of values, for example, the Permanganate number x 0.15% =% lignin in technical cellulose.

An additional aspect of the present invention relates to a method for treating pulverized cellulosic fibrous material by treating cellulosic fibrous material with a carbonate-containing solution to obtain pretreated cellulosic material, treating the pretreated cellulosic material with a cooking chemical for a sufficient time and at a sufficient temperature to obtain pulp and liquid liquor containing waste cooking chemical, liquid processing a liquor comprising spent cooking chemicals to produce carbonate-containing solution from the spent cooking chemical, and the use of the carbonate solution obtained from the spent cooking chemical, as a carbonate-containing solution in step a) above method.

A further aspect of the invention includes a method for treating pulverized cellulosic fibrous material comprising a) treating the cellulosic fibrous material with an acid solution b) treating the cellulosic fibrous material with a carbonate solution to obtain a pretreated cellulosic material, and c) treating the pretreated cellulosic material with a sulfur-containing cooking chemical for sufficient time and at a sufficient temperature to obtain pulp, at which, in at least one of stages b) and c), the cellulosic fibrous material is treated with anthraquinone. Sulfur-containing cooking chemicals can usually contain sodium hydroxide and sodium sulfide.

And another aspect of the invention includes pulp obtained by one of the above methods, in which the yield of pulp is greater than that obtained in methods known from the prior art. These and other aspects and advantages of the invention may be more fully understood in light of the discussion of the following description of the drawings.

Brief Description of the Drawings

The present invention will be better understood from the detailed description given in this document below, and from the accompanying drawings, which are given only as an illustration, and do not limit the present invention, where:

Figure 1 is a schematic diagram of a cooking process in accordance with aspects of the present invention.

Figure 2 is a schematic illustration of a chemical regeneration system that can be used in aspects of the invention.

Figure 3 is a graph comparing the yield of sorted cellulose in accordance with aspects of the present invention, with the yield of cellulose obtained in accordance with the currently known prior art.

Figure 4 is a graph comparing the values of the light scattering coefficient of a pulp obtained in accordance with aspects of the present invention and a pulp obtained in accordance with the prior art.

Figure 5 is a schematic illustration of the catalysis of the reactions of lignin and carbohydrate with anthraquinone, which is enhanced by aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Applicants have found that by treating pulverized cellulosic fibrous material, such as wood chips, in a first pretreatment step with a carbonate compound, for example substantially free of sulfur content of sodium carbonate, and then into a second cooking step, for example, soda cooking in the presence of anthraquinone ( AQ is used to refer to any anthraquinones), an improved pulp can be obtained. Improved pulp is also obtained if the pulp is subjected to acid treatment, before the first pretreatment step, then kraft cooking in the presence of anthraquinone follows. For example, the resulting pulp can be characterized by an increase in the yield of pulp, increased bleaching, increased strength, low amounts of rejected waste, among other useful properties.

In addition, by treating the wood chips with a carbonate-containing solution before processing the wood chips with a cooking chemical, the amount of cooking chemical used for the cooking process in the desired processing can be reduced. This improvement can have a significant impact on trying to reduce or eliminate the proportion of sulfur-containing cooking chemicals, which is especially true for sodium sulfide (Na ₂ S). As noted above, sulfur-free cooking processes, such as the soda process and the SAQ process, have received limited use in industry due to the relatively low quality of the produced technical pulp in comparison with the sulfur-containing kraft process. In addition, soda and SAQ processes typically require a larger amount of cooking chemical, such as sodium hydroxide (NaOH), compared to the kraft process. As will be discussed below, aspects of the present invention not only overcome these limitations, but also provide economically competitive pulp.

An additional aspect of the present invention relates to a method for treating pulverized cellulosic fibrous material, comprising: treating the cellulosic fibrous material with a substantially sulfur-free carbonate-containing solution to obtain a pretreated cellulosic material, treating the pretreated cellulosic material with a cooking chemical, such as an alkaline cooking chemical, for sufficient time at a sufficient temperature to obtain pulp and liquid slurry an eye containing the spent cooking chemical, treating the liquid liquor containing the spent cooking chemical to obtain a carbonate-containing solution from the spent cooking chemical, and using the carbonate-containing solution obtained from the spent cooking chemical as a carbonate-containing solution in step a) as described in paragraph 16 above. . carbonate-containing solution may contain sodium carbonate comprising from about 1% to about 12% sodium carbonate, as Na ₂ O. granulate Your said method may also include processing, such as oxygen delignification.

In one aspect, treating the liquid liquor containing the spent cooking liquor comprises concentrating enough liquid liquor to provide ashing, burning the concentrated liquid liquor to form a carbonate-containing melt, and introducing the liquid liquor into the melt to provide a carbonate-containing solution from the spent cooking chemical.

A further aspect of the invention includes a method for processing ground pulp fiber material, comprising a) treating the pulp fiber material with an acid solution, b) treating the pulp fiber material with a carbonate-containing solution, such as a sodium carbonate solution, to obtain a pre-treated cellulosic material, and c) pre-treating treated cellulosic material with a cooking chemical for a sufficient time at a sufficient temperature to obtain pulp, in which, at least in one of the stages b) and c), the cellulosic fibrous material is treated with anthraquinone.

Using processes and methods in accordance with aspects of the invention, several striking laboratory test results have been found. These improvements include: a decrease in the H-factor at the cooking stage, which turned out to be more significant than expected (the total H-factor of the first processing stage plus the H cooking factor is less than the H-factor in the absence of the first carbonate treatment stage with the same permanganate number; this is shown in Tables 2 and 3 below; increased pulp yield; increased bleaching; increased strength; less rejected waste). As is known from the prior art and for the purpose of this application, the H-factor is related to the way of representing cooking time and temperature as a dependence with one variable for delignification.

Figure 1 is a schematic diagram of a pulping process 10 for which aspects of the present invention are applied in which the pulped pulp fiber material 12, for example wood chips, is processed in a pre-treatment step 14 and cooked or pulped is cooked 16. The average person skilled in the art It is understood that although the term “wood chips” is used to facilitate discussion of the invention, aspects of the invention are not limited to wood processing. wood chips, but can be used to process any form of crushed cellulosic fibrous material, including, but not limited to, hardwood chips, softwood chips, sawdust, recycled fiber, recycled paper, agricultural waste such as cake, and other fibrous cellulosic material.

As is usually the case in the art, before loading into the process 10, the wood chips 12 can usually be brought to a conditioning state by treatment, for example, treated with water vapor to moisten the wood chips, the wood chips are heat treated, and as much air as possible is removed and other gases to increase the depth of penetration of the solutions for processing. The steam treatment of wood chips 12 can in practice be carried out, for example, in a horizontal steaming chamber or in a Diamondback® steaming chamber, both supplied by Andritz Inc. of Glens Falls, NY, before processing. In accordance with aspects of the invention, in the carbonate treatment stage 14 (also referred to as the c-stage, pre-treatment stage, first stage), the wood chips 12 are treated with a carbonate-containing solution 13, typically a sodium carbonate solution, although solutions of potassium carbonate and magnesium carbonate may also apply. In one aspect of the invention, this carbonate-containing solution may be substantially free of sulfur. One of ordinary skill in the art will appreciate that such a lack of sulfur may not mean that there is absolutely no sulfur in the carbonate solution in absolute terms, but that the solution is “substantially” sulfur free. After processing in the first stage 14, the wood chips 12 are then processed in the second or cooking stage 16, this is the cooking stage with the cooking chemical 20 for a sufficient time and at a sufficient temperature, to obtain technical pulp 18. Pulp 18 can usually be It is aimed at further processing, for example, washing with water, bleaching or sorting, among other generally accepted standard treatments. The carbonate-containing solution 13 can be obtained from various sources, including, but not limited to, commercially available carbonate and carbonate extracted from an adjacent process, such as a chemical regeneration cycle (for example, as shown and discussed in connection with Figure 2 below).

In accordance with aspects of the present invention, the carbonate-containing solution 13 may have a carbonate concentration of from about 1% to about 12% (expressed as Na ₂ O) based on wood. For example, a carbonate-containing solution may have a concentration of from about 2% to about 9% based on Na ₂ O for wood. The carbonate-containing solution may generally be provided in the form of an aqueous solution, such as a solution of carbonate in water, however, other compounds may be present. One of ordinary skill in the art understands the use of the term “about” when describing the percentage of carbonate and will take into account that it is difficult to make absolute measurements, and using the term “about” when describing the percentage of carbonate is common in the art. One kg / mol of Na ₂ COs (106 kg) is equivalent to one kg / mol of Na ₂ O (62 kg). Other carbonates, such as potassium and magnesium carbonates, may be added in terms of the molar equivalent of Na ₂ O. Carbonate treatment 14 is typically practiced at temperatures above 100 degrees C, for example in the range between about 120 degrees C and, approximately 200 degrees. In one aspect, carbonate treatment 14 may in practice be carried out in the range between about 120 degrees C and about 170 degrees C, for example in the range between about 120 degrees C and about 150 degrees C. The average person skilled in the art technicians understand the use of the term “approximately” when describing temperature ranges and will take into account that it is difficult to make absolute measurements, and the use of the term “approximately” when describing temperatures is common Asti technicians. This use of the term “approximately” is understood by one of ordinary skill in the art to indicate the boundaries of the measuring range of a processing parameter throughout the disclosure of this invention, including pressure, time, temperature, percentage of components used in the cooking process, and other related measurements . At such temperatures, treatment 14 can generally be practiced at elevated pressures from about 50 psi to about 150 psi. The pre-treatment stage 14 is usually practiced for a sufficient time, providing at least some advantage for the pulp obtained as a result of process 10. For example, the pre-treatment stage 14 can in practice be carried out for at least at least 5 minutes, but in practice can be carried out from about 15 minutes to about 6 hours, depending on the nature of the wood pulp, which is essentially wood chips 12, but the usual The practical time is from about 15 minutes to about 120 minutes.

In one aspect of the invention, after pre-treatment 14 and prior to cooking stage 16, at least some liquid liquor present can be removed or extracted from wood chips 12, as shown by 25. In one aspect, the extracted carbonate-containing liquor 25 can be processed, for example, in a regeneration system, disposed of, or otherwise reused. For example, in one aspect, the carbonate-containing liquor can be recycled and reused as a source or additive to carbonate 13.

After the pretreatment step 14, the carbonate pretreated wood chips 12 are then treated in the cooking step 16 with a cooking chemical for a sufficient time and at a sufficient temperature to produce pulp 18. Although one step 16 is shown in Figure 1, in accordance with one aspect inventions, however, one or more cooking stages 16 can be carried out. In accordance with one aspect of the invention, the cooking chemical 20 used in the cooking step 16 may be mainly sodium hydroxide (NaOH), then the cooking step 16 may be a “soda” cooking step. In another aspect of the invention, cooking chemical 20 may include NaOH and sodium sulfide (Na ₂ S), then the cooking step may be a “sulfate” treatment or a “craft” treatment. When the cooking step includes a kraft cooking step, in one aspect, the carbonate treatment step 13 may be with the preceding acid treatment step 22 (as discussed below). However, in accordance with aspects of the present invention, the cooking of the pre-treated wood chips 12 is practically carried out at the cooking stage 16 in the presence of at least some anthraquinone (AQ).

In one aspect, the cooking of wood chips 12 in the presence of AQ may be carried out as described in US Pat. No. 6,569,289 (the disclosure of which is incorporated herein by reference in its entirety). Applicants have found that pretreatment of wood chips 12 with carbonate, in particular Na ₂ CO ₃ , followed by SAQ cooking, provides pulp 18 having improved properties, such as increased yield, reduced lignin content and improved bleaching compared to the pulp provided processing methods of the prior art. For example, experiments performed by the applicants suggest that there may be some synergistic effects in the carbonate or carbonate-AQ pre-treatment and cooking process of the present invention, which, as a rule, are not predicted from prior art AQ processing methods.

In accordance with aspects of the present invention, at least some AQ or its derivatives or analogs are introduced in the pre-treatment stage 14, the cooking stage 16, or both stages 14 and 16. In one aspect, the AQ can be provided in its reduced form (which is a chemical reagent commonly referred to as AHQ, see Figure 5). In one aspect, an aqueous AQ solution may be added at the pre-carbonate treatment stage 14 (as indicated by dashed line 17 in Figure 1), for example, provided before, at the beginning, in the middle, at the end of the pre-treatment stage 14, or as some their combinations. The concentration of aqueous AQ introduced during step 14 can vary from about 0.01 wt.% To about 0.20 wt.% By weight of wood chips, but is typically in the range from about , 0.05 and up to about 0.10 wt.%. For the purposes of this application, AQ may be added at any time during the cooking process, as described in Figure 1.

In one aspect, AQ may be introduced at the cooking stage 16 (as indicated by line 21 in Figure 1), for example at the beginning, middle, end of the stage, or some combination thereof. The concentration of aqueous AQ introduced in cooking stage 16 can vary from about 0.01 wt.% To about 0.20 wt.% Based on wood chips, but usually from about 0.05 to. approximately 0.1 wt.% based on wood chips. In one aspect, AQ may be introduced in the carbonate treatment step 14, and removed from the cooking step 16; in another aspect, AQ can be introduced both at the carbonate treatment stage 14 and at the cooking stage 16.

According to aspects of the invention, when the first processing step 14, using a sodium carbonate solution as a carbonate-containing solution, for example a sulfur-free carbonate-containing solution, is followed by a second cooking stage 16 using NaOH (for example, loading approximately 13% NaOH from wood) and AQ (this represents the SAQ stage of cooking), amazing results were revealed in a laboratory test. A dose of NaOH equal to 13% based on wood corresponds to approximately 10% Na ₂ O, i.e. two kg / mol or 80 kg of NaOH are equivalent to one kg / mol or 62 kg of Na ₂ O. For example, in a laboratory test, when the first stage of carbonate treatment 14 is followed by the second stage of soda cooking 16 (with 13% NaOH based on wood) in In the presence of AQ, cooking has a significantly lower need for NaOH and allows one to obtain pulp with a yield close to that obtained with kraft cooking without increasing the amount of waste produced.

In another aspect of the invention, prior to pretreatment step 14, wood chips 12 can be treated with acid solution 19 in acid treatment step 22 (shown by a light bar in Figure 1). In the case where Kraft cooking is used in the presence of AQ in the cooking process, acid pretreatment 22 can be carried out, followed by carbonate treatment 14. Any solution containing acid can be used as acid 19, but in one aspect, acid 19 is preferably a sulfur-free acid solution, for example, an organic acid (such as acetic acid) or an inorganic acid (such as nitric or hydrofluoric acid). In one aspect, step 22 may be practiced in the presence of a naturally occurring acid, such as naturally occurring wood acid. An acidic solution 19 can be provided to produce an aqueous medium near wood chips 12 having a pH of about 6 or lower, for example, having a pH of from about 4 to about 6. Acid treatment in practice can be carried out at a temperature more than 50 degrees C, for example, at about 80 degrees C to about 160 degrees C. The acid treatment step 22 is usually practiced for a sufficient amount of time to provide at least some benefit to the cellulose pulp resulting from process 10. For example, the acid treatment step 22 may be practiced for at least 5 minutes, but may be practiced for from about 30 minutes to about 6 hours, and usually practically carried out for from about 30 minutes to about 90 minutes, depending on the nature of the paper composition, for example, the pH of wood chips 12. The amount of acid required may include any amount required to obtain some effect such as, for example, from 2 to 6% acetic acid at 120 ° C.

As shown in Figure 1, in one aspect of the invention, after acid treatment 22 and before carbonate treatment 14, at least some of the liquid medium present after acid treatment 22 can be removed or extracted from wood chips 12, as shown by extraction step 23 ( shown by a light dotted strip in Figure 1). In one aspect, the extracted acidic liquid medium 23 may be treated, for example, in a recovery system, disposed of, or reused. For example, in one aspect, the acid-containing liquid medium can be recycled and reused as a source or additive to acid 19.

Acid treatment can be carried out for wood chips 12, for example, the acid in step 22 can be ripe wood acid (which is wood stored for a period of time sufficient to spontaneously form a naturally occurring acidic liquid from wood). In another aspect, the acid in step 22 can be provided through a conventional acid hydrolysis process, for example, a process used to remove metals and other impurities from their wood chips 12. One such process is disclosed in US Pat. No. 5,338,366 (the disclosure of which is incorporated by reference in this document in its entirety).

In accordance with aspects of the invention, by combining an acid treatment step 22 with a carbonate pretreatment step 14 and a cooking step 16 comprising either NaOH (soda) and AQ, or NaOH and Na ₂ S (kraft) and AQ, or a combination of soda with AQ and Kraft with AQ, the consumption of chemicals (for example, the required amount of NaOH) can be reduced and the bleaching of the resulting pulp 18 is increased. This means that the amount of bleaching chemical required to achieve the desired whiteness can be reduced compared to treatments known in the art. In some aspects of the invention, it is also possible to see improvements in pulp yield by using the acid treatment process 22, followed by carbonate treatment 14, followed by SAQ. An improvement in bleaching is observed if cooking stage 16 is a kraft process. The lack of benefit in chemical consumption during SAQ cooking can be resolved through carbonate treatment step 14, and aspects of the invention can also improve bleaching of pulp through oxygen or, most likely, other single-electron oxidizing agents, such as chlorine dioxide, to the same extent . The acid treatment step 22 (A) can further improve the bleaching of the pulp obtained from both soda-AQ and kraft processing, especially after the oxygen (O) delignification step. The green liquor of the kraft processing (Na ₂ CO ₃ + Na ₂ S) can be used as a source of carbonate 13 if the cooking process 16 includes a kraft process.

Figure 2 is a schematic illustration of a chemical regeneration system 100 that can be used in aspects of the invention. The chemical recovery system 100 includes a standard recovery boiler or gasifier 110 for burning concentrated spent cooking liquor 112, such as black liquor, to produce a chemical product (not shown) containing sodium carbonate and sodium sulfide (in the case where black liquor includes black liquor kraft cooking), among other products of the combustion of black liquor, known from the prior art. In accordance with the generally accepted state of the art, a carbonate-containing product is dissolved in water in a vessel 114, which is a reservoir for green liquor, to obtain an aqueous solution (known as "green liquor") containing carbonate. In one aspect, green sulfide-containing liquor can be used for a carbonate-containing solution if the cooking step involves kraft cooking. Carbonate treatment with green liquor can be carried out with the previous acid treatment (stage 22 of Figure 1) before kraft cooking. The vessel 114 may be a green liquor tank or other suitable vessel known in the art. In accordance with the prior art, for practical implementation, an aqueous solution of sodium carbonate from the vessel 144 is usually sent for further transformations 120, which are caustification for the regeneration of NaOH for cooking or bleaching, for example, for oxygen delignification. In accordance with aspects of the invention, green liquor carbonate in the vessel 114 can be used as one of the sources of carbonate 13 for the pre-treatment stage 14 described in Figure 1.

The improvements and advantages afforded by aspects of the present invention have been investigated by applicants in processing vessels with laboratory batch loading, that is, in batch laboratory cooking boilers. The results of one such laboratory experiment are summarized in Table 1. Such vessels are commonly used for continuous and batch cooking processes. In the present invention, continuous or batch digesters may be used.

Table 1 summarizes the processing conditions and the results obtained in a series of laboratory experiments using periodic digestion boilers. The present invention corresponds to experiments 1, 3 and 4 in Table 1, in which at least a certain amount of sodium carbonate is added to the first stage of processing, followed by the stage of soda - AQ (SAQ) cooking. Test series number 2 is a control experiment, which corresponds to the standard stage SAQ cooking without pre-carbonate processing, and series of experiments 5 is a control experiment, which corresponds to standard Kraft cooking without AQ.

Table 1
The effect of carbonate pretreatment on soda / AQ cooking (CPC), confirmed by laboratory experiments with batch cooking room
series
experiences Na ₂ CO ₃
in the CDS ¹ H factor in CDS Final pH in CPC H factor SAQ Final pH in SAQ Output sort
tied
pulp Waste Permanganate number one 4.0% 312 7.6 1027 12.5 54.1 3.9 25.7 2 0 0 - 1506 ² 11.0 28,4 27.0 48.1 3 6.0% 544 8.9 1027 12.6 53,4 6.7 33.9 four 4.0 665 - 1027 12.6 55.3 0.3 22.8 5 - - - Craft - 1300 51.8 0.1 17.9 ¹ Based on Na ₂ O for wood chips.
² 10% Na ₂ O from NaOH + 6% Na ₂ O from Na ₂ CO ₃ . The remaining SAQ cooking was carried out with 10% Na ₂ O only from NaOH. When crafting, 12% Na ₂ O from NaOH is used.
³ Percentage of wood chips.
⁴ Permanganate number of sorted pulp.

In these laboratory experiments, 0.8 kg of sugar maple wood chip ( Acer saccharum ) (hardwood) was loaded into a laboratory digester. The carbonate pretreatment, summarized in Table 1, was carried out at 165 ° C and 170 ° C using Na ₂ CO ₃ in an amount of 4.0-6.0% based on Na ₂ O per wood shep, which is 6.8-10 , 3% Na ₂ CO ₃ . In series 1, 3 and 4, carbonate pre-treatment (CPC = carbonate pre-cooking) was followed by soda-AQ cooking with NaOH in an amount of 10% only based on Na ₂ O per wood chips. The initial approach to testing, after carbonate pretreatment, was to depressurize the batch boiler of a batch operation (which is “bleeding the digester”) and condense the gases released during the carbonate treatment stage (which is liquid runoff). NaOH and AQ were added to the condensed liquid effluent, and the liquid effluent with NaOH and AQ was reloaded into a digester with a sample of wood chips. The digester was then heated again to the digestion temperature.

Table 1 includes the "H-factor" for the pretreatment and cooking stages in the experiments. As is known in the art, the H factor stabilizes alkaline delignification rates in relation to the processing temperature. Usually, the higher the H factor, the more complete the processing. The H-factor in the second preheating process is included in the overall value for SAQ cooking. Table 1 also provides the pH values of the liquor in the digester after carbonate pretreatment and after soda-AQ treatment.

The advantages of the present invention are reflected in the indicators of “yield of sorted cellulose”, “waste” and “permanganate number”, which are presented in Table 1. As is known from the prior art, the yield of sorted cellulose is related to the percentage of the original wood chips present in the wood chips after processing and after sorting the pulp with the removal of wood chips, finely ground product, hairpins, etc., which have not been sufficiently subjected to the cooking process, and other non-fibrous felled residues. As is known in the art, a higher yield of sorted pulp is preferred. Waste is an indicator of the extent to which the original wood chips were not completely subjected to the cooking process, for example, what is emitted during sorting. Reduced waste means less wood is discarded or recycled. And also, as is known from the prior art, the permanganate number gives an idea of the relative indicator of the amount of undesired lignin present in the final pulp. Typically, higher permanganate numbers mean that more lignin is present in the pulp and more bleaching chemical is required to achieve the desired, pronounced bleaching. Thus, lower permanganate numbers are preferred.

The data in Table 1 confirm the advantages of the present invention. The data provided in Table 1 demonstrate that the method shown in Figure 1 provides a striking improvement in standard soda-AQ pulping. For example, as shown in Table 1, the waste values are a clear indication of the advantages of aspects of the present invention. According to Table 1, experiment series number 4 - corresponding to carbonate pre-treatment and soda-AQ cooking - provides a value of 0.3 for waste and a yield of sorted pulp of 55.3%. For comparison, experiment series number 2 — representing SAQ cooking in accordance with the present state of the art — provides a value of 27.0% for waste and a significantly lower yield of sorted cellulose of 28.4%. This suggests that aspects of the present invention more efficiently provide the cooking of more wood chips to obtain pulp, and at the same time support the receipt of a significant proportion of cellulose, as evidenced by the high yield. Existing low waste values provide a more efficient cooking process. Also, the data of Table 1 indicate that series of experiments No. 2 (corresponding to the present state of the art for SAQ cooking) provides a lower pH value at the end of SAQ than series of experiments 1, 3 and 4 (representing aspects of the invention) even if the use of NaOH was 10% of calculation of Na ₂ O for wood in all four cases. Applicants theoretically predict that reduced pH values for SAQ processes of the prior art are due to the lack of competition of NaOH, strong base, and Na ₂ CO ₃ in unproductive carbohydrate degradation reactions. Na ₂ CO ₃ remains in solution during SAQ cooking and is not a strong enough base to cause alkaline rearrangements necessary for lignin depolymerization and solubilization. When Na ₂ CO _{3 is} added by itself during pretreatment, reactive carbohydrates react with it because this substance is the only alkali present. Aspects of the present invention also include the addition of NaOH in step 16 to advance in the direction of depolymerization or degradation of lignin and, thus, can provide a more efficient cooking process.

Cooking without carbonate pretreatment in laboratory experiments was also investigated to provide a basis for comparison with aspects of the present invention. The results of these experiments are summarized in Table 2. In these experiments, a series of kraft pulp and SAQ pulp from sugar maple wood chips without carbonate pre-cooking were obtained. One of the kraft cooking experiments was carried out with an increased sulfide content and reduced alkali efficiency (EA) (10% Na ₂ O on wood chips from NaOH and 5% Na ₂ O on wood chips from Na ₂ S), see the second row of data in Table 2. This kraft cooking experience (second row of data in table 2) provided a higher yield of sorted pulp (approximately 1.0% increase in the yield of sorted pulp on wood chips) compared to the kraft experience with an increased EA value of 12 % Na ₂ O on wood chips from NaOH and 4% Na ₂ O on wood chips from Na ₂ S (see first row q data in Table 2). Both brews had approximately the same permanganate number for the unbleached product (which was 17.4 and 17.8). However, the pulp obtained using a lower EA value (which was 10% NaOH and 5% Na ₂ S in the second row of Table 2) showed a lower sensitivity to oxygen (O ₂ ) during delignification than the pulp obtained using more high EA values (12% NaOH and 4% Na ₂ S), which will be discussed below. Applicants understand that the difference between the permanganate number values obtained after exposure to O ₂ for these pulp is significant. As shown in Table 2, a series of SAQ experiments were also conducted. As shown, experiments with a changing EA value and with the mandatory presence of AQ in the amount of 0.1 percent per wood chips resulted in pulp having a permanganate number lower than 15.2 with a relatively low amount of waste.

table 2
Typical processing characteristics of control pulp using currently existing methods of kraft and soda-AQ cooking (which was carried out without carbonate pretreatment) Cooking process NaOH ¹ Na ₂ S ¹ Cooking temperature, ^o C ² H factor Output sort
pulp Waste
rejected ³ Permanent number ⁴ Craft 12.0% 4.0% 165 1297 51.9 0.1 17.4 Craft 10.0% 5.0% 165 1602 52.8
(52.9) ⁵ 0.2 17.8
(18.2) ⁵ Saq 11.0% 0 ⁶ 165 1602 51.7 8.0 42.0 Saq 12.5 0 ⁶ 165 1602 52.3 1,1 21.5 Saq 14.0 0 ⁶ 165 1602 52.8 0.6 19.3 Saq 14.0 0 ⁶ 170 1969 51.1 0.2 15,2 ¹ Based on Na ₂ O for wood chips.
² 90 minutes at temperature.
³ Percentage of wood chips.
⁴ Permanganate number of sorted pulp.
⁵ Repeat the experiment at a later date.
⁶ 0.1% AQ on wood chips.

Carbonate pre-cooking in accordance with one aspect of the invention was investigated in laboratory experiments. The results of these experiments are summarized in Table 3. Table 3 presents the processing conditions for the pre-treatment of wood chips with carbonate, followed by SAQ processing (series 1-5) and kraft processing (series 6 and 7). The advantages of carbonate pre-cooking in accordance with aspects of the invention are obvious when comparing the results presented in Table 2 (the current state of the art) with the results presented in Table 3. As an example, if batch 1 in Table 3 is compared with the standard SAQ process in In Table 2 (fifth row in Table 2), it can be seen that a 30-minute carbonate stage at 165 ° C (“C ₁ condition” see footnotes 2 and 3 in Table 3) reduces the alkali requirement for the SAQ stage from 14.0% (in Table 2) to 10% (in Table 3) in terms of n Na ₂ O. Comparison of the permanganate numbers indicates that the unbleached pulps obtained with a carbonate pretreatment, was slightly reduced kappa number (18.4 versus 19.3), and at the same time output the sorted pulp produced with carbonate pretreatment was slightly higher (53.1% compared to 52.8%). If the carbonate-SAQ process in accordance with aspects of the invention (e.g., series 5 in Table 3) is compared with the carbonate-craft process (e.g., series 7 of Table 3), you can see that a higher yield (1.0% on wood chips) obtained for carbonate-SAQ process in comparison with carbonate kraft processing. A higher yield is obtained in a more efficient process and, accordingly, a high yield of sorted pulp is desirable.

Aspects of the present invention may also result in a decrease in the H-factor for the cooking step more significantly than might be expected. When comparing the results described in Table 2 with the results in Table 3, it is obvious that the H-factor obtained from the treatment carried out without carbonate pretreatment is greater than the total H-factor for the process carbonate pretreatment plus cooking with a similar permanganate number . As an example, the H factor for pulp for which there was no pretreatment (lines 3-5 in Table 2) was over 1600 for SAQ. The H-factor for the pulp in the case of the SAQ stage with the previous two carbonate (C ₁ ) pretreatments (series 1 -2 in Table 3) was 1239, and for the C ₁ stage, the H-factor was 358, with a total value of 1597 for combined carbonate and SAQ treatments. The resulting carbonate pretreatment pulp with a permanganate number of 18.4 (row 1 of Table 3) had an improved yield of sorted pulp, improved bleaching, resulting in a lower amount of waste than pulp without pretreatment. A further comparison illustrating the advantages of aspects of the present invention can be found in Figure 3, which is discussed below.

Table 3
The effect of carbonate pretreatment on soda-AQ- and kraft cooking of sugar maple wood chips Experiment Series Number The final pH value in the C-stage H-factor for cooking Process ¹ Sorted output
pulp Waste
rejected Permanent number ² one 8.4 (C ₁ ) ³ 1239 Saq 53.1 0.1 18,4 2 7.9 ⁴ (C ₁ ) 1239 Saq 52.7 0.1 17,2 3 8.4 (C ₁ ) 1239 SAQ ⁵ 54.7 0.8 26,4 four 9.8 (C ₁ ) 1445 SAQ ⁵ 53.9 0.2 22.7 5 ~ 7.0 (C ₂ ) 1239 Saq 52,2 0.1 16.7 6 8.4 (C ₁ ) 1027 Craft 52.1 0.3 18.0 7 ~ 7.0 (C ₂ ) 1239 Craft 50.8 0.1 15.6 ¹ 10% Na ₂ O for SAQ; 8.5% and 3.0% of NaOH and Na ₂ S in Kraft cooking.
² Permanganate number of sorted pulp.
³ C ₁ = 30 minutes at 165 ° C; C ₂ = 60 minutes, 4.0% Na ₂ O on wood chips for all series except Series 4, where 5.0% was used.
⁴ AQ was added to the C-stage instead of SAQ.
⁵ Only 9% Na ₂ O in SAQ.

After the cooking experiments discussed above and summarized in Table 2 and Table 3, the cellulosic material was bleached. The sequence of bleaching processes used in the laboratory test was OD ₀ EpD ₁ (where O represents the alkali treatment step and O ₂ ; D ₀ represents the chlorine dioxide delignification step with a final pH of 2-3; Ep represents the alkaline extraction step with hydroxide sodium and hydrogen peroxide for additional delignification; D ₁ represents the stage of clarification with chlorine dioxide with a final pH of 3.4-4.5). The use of chlorine dioxide in the Do step was carried out based on the formula: wt.% Chlorine dioxide per pulp = 0.076 x permanganate number of treated O ₂ pulp. In accordance with a laboratory test, the applicants found that a value of 21.5 for the permanganate number of pulp obtained in the soda-AQ pulping experiment (that experiment, the data of which are presented in the fourth row of Table 2) can be obtained using 12.5 % Na ₂ O; however, this pulp was harder to bleach than the pulp obtained using 14.0% Na ₂ O (the experiment whose data are presented in the fifth and sixth lines of Table 2). A decrease in permanganate number due to O _{2 is} usually an indicator of a decrease in bleaching. In accordance with aspects of the invention, bleaching of pulp obtained by soda-AQ cooking is improved by carbonate pretreatment. One of ordinary skill in the art will understand, although this specific sequence of bleaching processes was used in this study, in accordance with aspects of the invention, any suitable known bleaching process can be used, including bleaching processes that exclude the use of chlorine compounds, which are completely free chlorine free (TCF) whitening processes excluding elemental chlorine, such as elemental chlorine-free (ECF) whitening processes s.

Figure 3 is a graph comparing the yield of sorted cellulose as a function of permanganate number after oxygen delignification for aspects of the present invention and the current state of the art. As shown, aspects of the invention provide pulp that is easier to bleach compared to standard methods of the current state of the art. As is known from the prior art, the percent yield of sorted cellulose is the ratio of the mass of pulp produced in the process to the mass of wood loaded into the process, after the pulp is sorted to remove knots, chips and other undesirable material. Preferred is a higher yield of sorted pulp. The permanganate number after treatment with O _{2 is} correlated with the lignin content in the pulp subjected to cooking and oxygen delignification. As is known in the art, a lower permanganate number value is preferred. As for Figures 3 and 4, the following notation is used: A = acid; C = carbonate pretreatment; Kr = crafting; SAQ = soda-anthraquinone treatment. The letter "(M + N)" means that the treatment was carried out at M% NaOH for wood, calculated as Na ₂ O and N% Na ₂ S for wood, in terms of Na ₂ O. The methods of the present invention further include processing type of oxygen delignification, resulting in obtaining a pulp with a reduced permanganate number, after processing the type of oxygen delignification, at a given output of sorted cellulose, in comparison with the pulp obtained by the method without the practical application of the preliminary stage 14 processing.

As shown in Figure 3, there is a striking improvement in pulp in the case of carbonate pre-treatment with soda-AQ cooking ("X" C-SAQ) compared to soda-AQ cooking without pretreatment ("▲" SAQ). In accordance with the results presented in Figure 3, the permanganate number obtained in the case of carbonate pretreatment followed by soda-AQ (“X” C-SAQ) cooking reaches a lower value after O ₂ bleaching than the permanganate number for soda-AQ pulp without pretreatment ("▲" SAQ). As an example, after treatment with O _{2, the} permanganate number in the case of C-SAQ ("X") is slightly higher than 8 with a percentage yield of sorted pulp over 52%, and after treatment with O _{2 the} permanganate number in the case of SAQ ("▲") is approximately 10.5 with a comparable yield of sorted pulp of approximately 52.5%. This is, with comparable yields of sorted cellulose, an aspect of the present invention providing a lower permanganate number compared to the current state of the art. In view of the above, carbonate treatment reduces the permanganate number (both for unbleached pulp and after the O-stage).

In these laboratory experiments, the loss in cellulose yield at all stages of the oxygen treatment was approximately 1.4-1.8%. Small differences in yield loss during the O-stages are insignificant when converted to “percent on wood chips”. Carbonate treatment or acid treatment followed by carbonate pretreatment (which is the “AC pretreatment”) does not improve the yield of fiber obtained by kraft pulping. However, as shown in Figure 3, carbonate and acid + carbonate pretreatments (“X” C-SAQ and “*” AC_SAQ) clearly improve the yield of the SAQ cooking step (“▲”). This means, in accordance with aspects of the invention, that a higher yield of sorted pulp is achieved compared to standard SAQ pulping methods.

Figure 4 is a graph comparing the permanganate number of fully bleached pulp as a function of oxygen delignification performed for aspects of the present invention and the current state of the art. The ordinate in Figure 4 is the light scattering coefficient (LAC) value for fully bleached pulp after bleaching OD _o EpD ₁ , and the abscissa is the permanganate number obtained after treatment with O ₂ . The analysis of Figure 4 shows that the pulp after standard soda-AQ cooking ("▲") is more colored (which means that it has higher LAC values) than the pulp after kraft cooking ("filled diamond"). However, cellulose from soda-AQ cooking and after acidic (A) and carbonate pretreatment (C) (“open triangle” and “open diamond”) in accordance with aspects of the invention has an equivalent or slightly reduced color than cellulose after kraft cooking without pretreatments.

Additional laboratory tests were performed to compare the properties of bleached kraft pulp, bleached acid-carbonate-kraft pulp and bleached acid-carbonate-soda-anthraquinone pulp. Some properties of bleached kraft pulp according to the current state of the art, acid-carbonate (AC) -kraft pulp according to an aspect of the invention, and acid-carbonate (AC) -SAQ pulp by cooking in accordance with an aspect of the invention, sugar maple wood chips are documented in Table 4. As shown in Table 4, soda-AQ pulp obtained by pretreatment with both acid and carbonate, resulting in a floor learned with improved yield. The yields of sorted pulp were the highest for AC-SAQ cooking, 53.2, compared with a yield of less than 52 both for kraft cooking of the current state of the art and for AC-kraft pulping. AC pretreatment increased the final bleaching degree of pulp obtained by kraft cooking from 91.0 to 92.6.

Table 4
Properties of bleached pulp obtained by the Kraft process in accordance with the current level of technology, and obtained by AC-Kraft and AC-SAQ pulping processes in accordance with the present invention. craft AC craft AC-SAQ Permanganate number of unbleached pulp 17.4 17.8 19.3 Sorted pulp yield ¹ 51.8 51,4 53,2 Rejected waste ¹ 0.1 0.1 0.1 Permanganate number after processing O ₂ 9.2 8.7 9.8 The degree of bleaching after O ₂ processing ² ~ 55.0 57.4 54.1 ODEp degree of whitening 82.8 83.5 82.3 The final degree of whitening 91.0 92.6 91.2 Final LAC ³ , m ² / kg 0.182 0.121 0.173 Bleached Pulp Yield ¹ 49.8 49.5 51,2 ¹ % on wood chips.
² % Elrepho.
³ Light scattering coefficient (LAC) = 40.8 m ² / kg for all three pulp samples.

When pulping is carried out in accordance with aspects of the invention, as shown in Figure 1, at least a certain amount of A-stage effluent (acid stage) can be replaced, for example, from 50% to 75% of the total amount of A stage effluent, s using a carbonate-containing solution. In one aspect, at least some or possibly all of the carbonate stage effluent can be transferred together with wood chips to the Kraft or SAQ stage. In laboratory experiments, which have already been reported, the carbonate stage effluent was returned after passing through a condensation apparatus. NaOH was introduced into the stock in the form of granules and AQ in the form of a powder was dissolved in a condensed stock. The effluent containing carbonate and AQ was then returned to the laboratory digester to the SAQ stage. A solution of sodium sulfide and NaOH pellets were added to the carbonate stage effluent in a Kraft cooking vessel. For the intended use of this application, the degree of whitening is presented as a percentage of opacity of Elrepho.

Applicants have suggested that the use of some or all of the carbonate stage effluent may be important for aspects of the invention, for example, for a carbonate-SAQ process. Applicants are convinced that this is possible because the possibility is assumed that the carbonate runoff may contain many low molecular weight carbohydrates with reducing terminal groups. It is assumed that the dissolution of carbohydrates during the carbonate stage can be approximately 5% of the initial mass of wood chips (dried base). Applicants are convinced that mixed hydrolysis of carbohydrates and the formation of new reducing end groups are possible with each hydrolysis. A high concentration of reducing terminal groups will reduce the AQ content, while a higher proportion of it will form AHQ (anthraquinone), which is an active delignification catalyst. The AQ / AHQ catalytic cycle is shown schematically in Figure 5. In addition, when the reducing end group in the solid phase is oxidized to a carboxylic acid, it becomes resistant to the alkaline peeling reaction of the cortex, which reduces the molecular weight of carbohydrates and reduces the yield of cellulose. The above hypothesis may explain why the carbonate step improves cellulose yield in the case of SAQ cooking, but not in the case of kraft cooking. The oxidation of the reducing end groups to carboxylic acids is not considered a significant reaction (or at least occurring) in the Kraft process or in the process of soda cooking without adding AQ.

To further confirm the advantages of aspects of the invention, additional laboratory studies were performed with wood chips from a mixture of wood species. As an example, a wood chip mixture comprising approximately 60% of the wood of the deltoid family ( Populus deltoids ), approximately 20% of white birch ( Betula papynfera ), and approximately 20% of sugar maple was used. The results of kraft cooking of the current state of the art, soda-AQ cooking of the current state of the art and cooking in accordance with aspects of the invention, such as with acid and acid / carbonate pretreatments, are presented in Table 5. Conditions for acid pretreatment were:

A ₁ : 20 min at 150 ° C with 1.5% acetic acid on wood chips (final pH ~ 3.5); and

A ₂ : 60 min at 120 ° C with 3.0% acetic acid (final pH 3.2).

As indicated in Table 5, A ₁ pretreatment provided cellulose after soda-AQ cooking with the highest degree of bleaching (which represents the "Final Value") (90.8) than kraft cooking (89.9), but yield pulp was slightly lower. The pretreatment with acid-carbonate-SAQ cooking, which takes place under mild A ₂ conditions, provided the highest yield of pulp (54.2%) than standard kraft cooking and SAQ cooking. A ₂ C-SAQ treatment also gives a higher degree of bleaching (89.2) than SAQ cooking (88.4), but less than kraft cooking (89.9). In one aspect of the invention, applicants are certain that stringent acid (A) stage conditions may be more preferred than A ₂ acid treatment, but less preferred than A ₁ acid treatment for this wood chain composition. Also, as shown in Table 5, the tensile strength coefficient obtained after 2000 pulsed-field ionization (PFI) clarification cycles, as indicated by the "tensile strength coefficient", for acid-craft cooking (78.3) and acid SAQ cooking (86.1) was lower than with kraft cooking (94.4). However, acid-carbonate-SAQ cooking had the highest ratio (which is 100.2), further emphasizing the advantages of aspects of the invention. From the results that are presented in Table 5, it appears that cellulose with a large yield and possibly a high content of hemicelluloses requires less clarification. There were no significant differences for the tensile-tensile strength curves.

Table 5
Impact of Acid and Acid / Carbonate Pretreatments on Kraft and Soda-AQ Cooking of Mixed Hardwood craft A ₁ craft Saq A ₁ -SAQ A ₂ C ₁ -SAQ ¹ Sorted pulp yield 53,2 51.1 53.0 52.7 54,2 Rejected waste 0.2 0.1 0.3 0.1 0.2 Permanganate number of unbleached pulp 16.7 17.1 16.6 15.9 18.9 Permanganate number About _2- bleached pulp 9.6 9.6 9.8 9,4 9.5 The final value of the degree of whitening
(% elrepho) 89.9 91.8 88.4 90.8 89.2 CSF ² 412 489 429 375 Tensile Strength Factor ² 94.4 78.3 86.1 100,2 ¹ EA = IO% Na ₂ O; 14.0% for other brews.
² Canadian Standard for Pulp Dewatering Rate and Tensile Strength Factor at 2,000 PFI Cycles (Light Load) for O ₂ - Lightweight Pulp.

In addition, the mild conditions of the carbonate stage have been studied to fully understand the benefits of carbonate-SAQ cooking and to further distinguish between the present invention and the earlier study in the '241 patent, where anthraquinones were not included. The results of this study are summarized in Table 6. A wood chips composition was prepared as consisting of 50% sugar maple, 40% deltoid poplar and 10% white birch. The carbonate treatment steps in accordance with aspects of the invention were carried out at 130 ° C and 140 ° C with either 3.0 or 5.0% Na ₂ CO ₃ loading (based on Na ₂ O) onto the wood and over a period of time either 30 or 60 minutes. In these experiments, it took approximately 30-35 minutes to reach maximum temperature. About 70% of the carbonate stage effluent was drained and disposed of after carbonate treatment. Carbonate stock was replaced with distilled water when the cooking chemicals were added at the SAQ or kraft stage.

Table 6
Exposure to carbonate pre-cooking at 130 degrees C and at 140 degrees C Batch number Temperature C stage
° C Time min Final pH H factor in S or K ² Sorted pulp yield ³ Scrap waste ³ Permanent number ⁴ one 130 (3.0%) ⁵ thirty 8.0 816 (S) 55.1 2,8 28.8 2 130 (3.0%) 60 7.8 816 (S) 55.8 1.4 27.6 3 130 (5.0%) thirty 9.1 816 (S) 55.1 1,1 23,4 four 140 (3.0%) thirty 8.2 816 (S) 55.0 1,5 24.4 (12.3) 5 140 (3.0%) 60 7.9 816 (S) 55.8 0.6 23.1 (10.7) 6 140 (3.0%) 60 7.5 816 (C) 54,4 0.4 20.9 7 140 (5.0%) thirty 8.6 816 (S) 54.5 0.3 19.3 (10.2) 8 - - 992 (W) ⁶ 53.5 0.5 17.3 (9.0) 9 - - 992 (S) 54,2 1,0 22.6 ¹ Final pH value of the carbonate cooking stage (C stage).
² S = SAQ; K = craft.
³ percent on wood chips.
⁴ Permanganate number of sorted pulp; the value obtained after treatment with O ₂ is shown in parentheses.
⁵ Na ₂ CO ₃ used, based on% Na ₂ O per wood chips.

In accordance with the result presented in Table 6, the best results were obtained in the case of carbonate-SAQ treatment, with a duration of carbonate stage of 60 minutes, at 140 degrees C, with 3% Na ₂ CO ₃ on wood chips (based on Na ₂ O) (for example, see series of experiments 5). The cellulose of experiment series 5 was obtained with the yield of sorted cellulose based on wood chips approximately 2.0% higher than in series of experiments 8 (reference to kraft cooking), and only with a loss of advantage of 1.7 units of permanganate number after oxygen delignification in comparison with a series of experiments 8. When comparing kraft cooking with pre-treatment (series of experiments 6) with carbonate-SAQ cooking (series of experiments 5), there was an advantage in yielding approximately 1.0% to wood chips. This yield advantage results in a total profit increase of approximately $ 4M / year for a typical chemical brewery.

In addition to the above, the combined H-factor of carbonate (C) and soda-AQ stages in a series of experiments 5 is 897 (81 + 816) to obtain cellulose having approximately the same permanganate number (23.1 compared to 22.6), higher yield (55.8 compared to 54.2) and less rejected waste (0.6 compared to 1.0) when compared to cellulose obtained by SAQ in accordance with the current level of technology without prior processing, but with an H-factor of 992 (series of experiments 9). The time spent on the carbonate stage can have a significant effect on the resulting pulp. In laboratory experiments, an additional 30 minutes of the carbonate stage at pH ~ 8 (see series of experiments 4 compared to series of experiments 5) resulted in an advantage of 1.6 units of permanganate number after soda-AQ cooking and oxygen delignification. Moreover, an additional 30 minutes of the carbonate stage provides a higher yield of sorted pulp. Moreover, it is believed that a larger number of reducing end groups was obtained as a result of an additional 30 minutes of the carbonate stage, a longer final cooking time turns more rejected waste into sorted pulp.

Aspects of the invention may be practiced in batch devices (such as, but not limited to standard, SuperBatch® or Rapid Displacement Heating) or continuous (such as, but not limited to standard for soda cooking, standard for kraft cooking, Lo- Solids® Cooking, EMCC® Cooking, ITC® Cooking, and Compact Cooking), in which an autoclave (as required for carbonate processing) is used for any or all stages of acid, carbonate processing and cooking. Aspects of the invention are also suitable for preparing for 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. For batch systems, standard devices, such as pumping liquor to the reaction vessel, can be used to replace liquor in the digester, or liquor can be removed from the digester by gravity or vacuum pumping devices before a new liquor is added to the digester. All liquors can be preheated using methods known in the art, such as SuperBatch or RDH liquor recovery methods. In addition, heating of the liquor can be performed in the reaction vessel by means of a circulating closed system or by adding hot steam.

Aspects of the present invention described herein provide a pulp pretreatment process and a cooking process that provides useful improvements to the processing of wood chips and related pulped pulp materials in accordance with the current state of the art. As it becomes clear from the test data presented in this document, pre-treatment of wood chips with a carbonate-containing solution in the presence or absence of anthraquinone can lead to cellulosic pulp in high yield, with less rejected waste, with increased strength properties, and requires fewer chemicals both for receiving and for bleaching.

Although several aspects of the present invention have been described and proven in this document, alternative aspects can be provided by a person skilled in the art to achieve the same objectives. In accordance with this, it is the intention of the appended claims to cover all such alternative points as falling within the scope of the actual essence and scope of the invention.

Claims (50)

1. A method of processing powdered cellulosic fibrous material, including:
a) treating the cellulosic fibrous material with a sulfur-free carbonate-containing solution to obtain a pre-treated cellulosic material and, finally, a) a solution having a pH of from 7 to 9.1; and
b) treating the pre-treated cellulosic material with a cooking chemical for a sufficient time and at a sufficient temperature to obtain a pulp;
in which at least one of a) and b) the cellulosic fibrous material is treated with anthraquinone. 2. The method according to claim 1, in which the cellulosic fibrous material is treated with anthraquinone in a). 3. The method according to claim 1 or 2, in which the pre-treated cellulosic fibrous material is treated with anthraquinone in b). 4. The method according to claim 1 or 2, in which the carbonate-containing solution includes a solution containing sodium carbonate. 5. The method according to claim 4, in which the solution containing sodium carbonate includes from 1% to 5% sodium carbonate based on Na ₂ O per wood, and processing takes place for 15-120 minutes at a temperature of from 120 to 200 ° C. 6. The method according to claim 5, in which the solution containing sodium carbonate includes from 2% to 4% sodium carbonate based on Na ₂ O per wood, and processing takes place for 15-120 minutes at a temperature of from 120 to 170 ° C. 7. The method according to claim 1, wherein the sulfur-free carbonate-containing solution includes a sulfur-free sodium carbonate solution. 8. The method according to any one of paragraphs.1, 2 or 7, in which the cooking chemical includes sodium hydroxide. 9. The method according to any one of claims 1, 2 or 7, in which the cooking chemical consists of sodium hydroxide. 10. The method according to any one of paragraphs.1, 2 or 7, in which the method further includes, before a), c), processing the crushed fibrous material with an acid solution. 11. The method according to any one of paragraphs.1, 2 or 7, in which the method further includes, after c) and before a), d), extracting at least a certain amount of the acid solution from the cellulosic fibrous material . 12. The method according to claim 4, in which the sodium carbonate solution comprises from 1% to 5% sodium carbonate based on Na ₂ O per wood chips. 13. The method according to item 12, in which sodium carbonate includes from 2% to 4% sodium carbonate based on Na ₂ O on wood chips. 14. The method according to any one of paragraphs.1, 2 or 7, which a) is carried out in practice at a temperature exceeding 100 ° C. 15. The method according to any one of paragraphs.1, 2 or 7, which a) is carried out in practice at a temperature between 120 ° C and 170 ° C. 16. The method according to any one of claims 1, 2 or 7, which a) is carried out in practice at a temperature between 120 ° C and 150 ° C. 17. The method according to any one of paragraphs.1, 2 or 7, which a) is carried out in practice for a time from 15 minutes to 120 minutes 18. The method according to any one of paragraphs.1, 2 or 7, in which the method is carried out in practice continuously. 19. The method according to any one of claims 1, 2 or 7, in which the method further includes an oxygen delignification treatment. 20. The method according to any one of claims 1, 2 or 7, in which the treatment with anthraquinone includes an aqueous solution of anthraquinone having a concentration of from 0.01 wt.% To 0.20 wt.% On wood chips. 21. The method according to any one of claims 1, 2 or 7, in which the treatment with anthraquinone includes an aqueous solution of anthraquinone having a concentration of from 0.05 wt.% To 0.10 wt.% On wood chips. 22. The method according to any one of paragraphs.1, 2 or 7, in which anthraquinone is administered after a) and includes a concentration of an aqueous solution of anthraquinone from 0.01 wt.% To 0.20 wt.% On wood chips. 23. The method according to any one of paragraphs.1, 2 or 7, in which the processing of the pre-treated cellulosic material with a cooking chemical further includes obtaining liquor containing spent cooking chemical; and in which the method further includes:
treating the liquor containing the spent cooking chemical to obtain a carbonate-containing solution from the spent cooking chemical; and
the use of a carbonate-containing solution obtained from a spent cooking chemical as a carbonate-containing solution in a). 24. The method according to item 23, in which the processing of liquor containing spent cooking chemical, includes:
sufficient liquor concentration to provide ashing,
burning concentrated liquor to form a melt containing carbonate; and
introducing liquor into the melt to provide a carbonate-containing solution from the spent cooking chemical. 25. The method according to item 23, in which the carbonate-containing solution includes from 2% to 5% sodium carbonate based on Na ₂ O on wood chips. 26. The method according to any one of claims 1, 2 or 7, in which the method further includes an oxygen delignification treatment and at least one bleaching step, in which the method results in a pulp having a whiteness greater than than 88% elrepho. 27. A method of processing ground pulp fibrous material, comprising;
a) processing the cellulosic fibrous material with an acid solution;
b) treating the cellulosic fibrous material with a carbonate-containing solution to obtain pre-treated cellulosic material; and
c) treating the pre-treated cellulosic material with sulfur-containing or sulfur-free cooking chemicals, but containing hydroxide anion (OH ^- ), for a sufficient time at a sufficient temperature to obtain a pulp;
wherein in at least one of b) and c) the cellulosic fibrous material is treated with anthraquinone. 28. The method according to item 27, in which the cellulosic fibrous material is treated with anthraquinone in b). 29. The method according to item 27 or 28, in which the pre-treated cellulosic fibrous material is treated with anthraquinone in C). 30. The method according to any one of paragraphs.27 or 28, in which the carbonate-containing solution includes a solution containing sodium carbonate. 31. The method according to any one of paragraphs.27 or 28, in which the carbonate-containing solution includes Kraft green liquor. 32. The method according to any one of paragraphs.27 or 28, in which the carbonate-containing solution includes a solution containing sodium carbonate having a concentration of from 1% to 12% sodium carbonate based on Na ₂ O per wood, preferably from 2% up to 9% sodium carbonate based on Na ₂ O per wood, and processing takes place for 15-120 minutes at a temperature of more than 100 ° C, preferably from 120 ° C to 170 ° C, more preferably from 120 ° C to 150 ° C . 33. The method according to any one of paragraphs.27 or 28, in which the solution containing sodium carbonate includes an aqueous solution having a concentration of from 3% to 9% carbonate based on Na ₂ O per wood. 34. The method according to any one of paragraphs.27 or 28, in which the method further includes, after a) and before b), d) removing at least a certain amount of the acid solution from the cellulosic fibrous material. 35. The method according to any one of paragraphs.27 or 28, in which b) is practically carried out at a temperature greater than 100 ° C. 36. The method according to any one of paragraphs.27 or 28, in which b) is practically carried out at a temperature between 120 ° C and 170 ° C. 37. The method according to any one of paragraphs.27 or 28, in which b) is practically carried out at a temperature between 120 ° C and 150 ° C. 38. The method according to any one of paragraphs.27 or 28, in which b) is practically carried out for from 15 minutes to 120 minutes 39. The method according to any one of paragraphs.27 or 28, in which the method is practically carried out continuously. 40. The method according to any one of paragraphs.27 or 28, in which the method further includes an oxygen delignification treatment. 41. The method according to any one of paragraphs.27 or 28, in which the treatment with anthraquinone comprises a concentration of from 0.01 wt.% To 0.20 wt.% On wood chips. 42. The method according to any one of paragraphs.27 or 28, in which the treatment with anthraquinone comprises a concentration of from 0.05 wt.% To 0.10 wt.% On wood chips. 43. The method according to any one of paragraphs.27 or 28, in which anthraquinone is administered after b), and in which the treatment with anthraquinone comprises a concentration of from 0.01 wt.% To 0.20 wt.% On wood chips. 44. The method according to any one of paragraphs.27 or 28, in which the processing of the pre-treated cellulosic material with a sulfur-containing cooking chemical further includes the production of liquor containing the spent cooking chemical; and in which the method further includes:
processing liquor containing the spent cooking chemical to obtain a carbonate-containing solution from the spent cooking chemical; and
the use of a carbonate-containing solution obtained from a spent cooking chemical as a carbonate-containing solution in b). 45. The method according to item 44, in which the processing of liquor containing spent cooking chemical, includes:
sufficient liquor concentration to provide ashing,
burning concentrated liquor to form a melt containing carbonate; and
introducing liquor into the melt to provide a carbonate-containing solution from the spent cooking chemical. 46. The method according to any one of claims 1, 2 or 7, wherein b) treating the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material comprises treating the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material and, finally a) a solution having a pH of from 7.0 to 8.9. 47. The method according to any one of claims 27 or 28, wherein b) treating the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material comprises treating the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material and, at the end, a) a solution having a pH of from 7.0 to 9.1. 48. The method according to any one of paragraphs.27 or 28, in which b) processing the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material comprises treating the cellulosic fibrous material with a carbonate-containing solution to obtain a pretreated cellulosic material and, at the end, a) a solution having a pH of from 7.0 to 8.9. 49. The method according to any one of paragraphs.27 or 28, in which the carbonate-containing solution includes from 1% to 5% sodium carbonate based on Na ₂ O per wood. 50. The method according to any one of paragraphs.27 or 28, in which the carbonate-containing solution includes from 2% to 4% sodium carbonate based on Na ₂ O per wood.

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