Kraft pulp production process from mixtures of hardwoods and softwoods, kraft pulp obtained by the process, and paper products produced from this pulp.

Description

1 / 33 Kraft pulp production process from mixtures of hardwoods and softwoods, kraft pulp obtained by the process, and paper products produced from this pulp. Area of ​​the Invention

[0001] The present invention relates to a process for producing Kraft pulp from mixtures of hardwood and softwood species. Additionally, the invention relates to paper products produced from the high-yield pulp obtained. State of the art

[0002] Wood is generally composed of cellulosic fibers, hollow cells consisting of a lumen (empty interior space) and a cell wall, composed mainly of cellulose, hemicelluloses and lignin (Fengel, D. and Wegener, G., Wood—Chemistry, Ultrastructure, Reactions, 2ndEdition, Walter de (Gruyter, Berlin, 1989). Lignin is distributed heterogeneously in the cell wall, and is more concentrated in the so-called middle lamella and cell corners, the outer layer of the fibers, responsible for cohesion in the three-dimensional structure of wood (Saka, SR; Thomas, J.; Gratzl, JS; Abson, D., Topochemistry of Delignification in Douglas-fir Wood with Soda, SodaAnthraquinone and Kraft Pulping as Determined by SEMEDXA*, Wood Science and Technology, 16, 139-153, 1982).

[0003] The industrial process of producing cellulose pulp aims at the disintegration of Petition 870240022363, dated 03 / 15 / 2024, page 8 / 40 2 / 33 three-dimensional structure of wood and individualization of the cellulose fibers constituting its matrix. Generally, this can be achieved in two ways: mechanically or chemically, or by combining these two approaches. Mechanical processes basically consist of grinding the wood or its chips, with yields (mass of pulp / mass of wood) x 100) greater than 90%. In contrast, in chemical cooking, whose objective is the dissolution of lignin in the wood in order to release the fibers from the matrix, approximately half of the wood constituents, including lignin, are dissolved, giving a pulp production yield of about 45-55%.

[0004] One of the most widely used chemical processes industrially for the production of cellulose pulp from wood is Kraft cooking, or sulfate cooking. This chemical process consists of cooking the wood in a cooking liquor usually composed of sodium hydroxide and sodium sulfide, at temperatures of around 140 to 180 °C, in pressurized reactors (Ek, Monica; Gellerstedt, Goran; Henriksson, Gunnar; Pulp and Paper Chemistry and Technology Volume 2, Pulping Chemistry and Technology, 2009, De Gruyter, Berlin).

[0005] No chemical method is selective enough to remove all the lignin present in the wood, ending the cooking process with a residual lignin content of 1-5% in the cellulosic fiber of the pulp produced. The temperature and duration of a cooking process determine the degree of delignification, and this can be Petition 870240022363, dated 03 / 15 / 2024, p. 9 / 40 3 / 33 measured by the Kappa Index (IK), which is proportional to the remaining lignin content in the pulp. Another relevant factor for monitoring Kraft cooking is the H factor, which combines the time and temperature variables into a single variable. Numerically, it corresponds to the integral of the relative delignification rate with respect to the time variable (Ek, Monica; Gellerstedt, Goran; Henriksson, Gunnar; Pulp and Paper Chemistry and Technology Volume 2, Pulping Chemistry and Technology, 2009, De Gruyter, Berlin).

[0006] Species whose wood is used in the production of cellulose pulp are classified as softwood (such as pine) or hardwood (such as eucalyptus), differing in their anatomy and chemical composition (Fengel, D. and Wegener, G.; Wood—Chemistry, Ultrastructure, Reactions, 2ndEdition, Walter de Gruyter, Berlin, 1989).

[0007] Softwood contains more lignin and less cellulose than corresponding hardwoods, and its lignin is also less reactive and the delignification kinetics are slower due to its structure being more resistant to chemical attack. Cooking softwoods therefore requires more drastic cooking conditions in terms of H-factor and chemical load than those used for hardwoods (Fengel, D. and Wegener, G.; Wood—Chemistry, Ultrastructure, Reactions, 2nd Edition, Walter de Gruyter, Berlin, 1989). On the other hand, softwoods, due to their chemical composition of extractable compounds, release components during cooking that give rise to tall oil which, not being Petition 870240022363, dated 03 / 15 / 2024, page 10 / 40 4 / 33 removed, complicates the evaporation process of the black liquor (liquid fraction containing byproducts of the wood cooking process) produced and increases pitch deposition in the pulp produced.

[0008] In the cooking of hardwoods, typical Kappa indices and yields of 15-19% and 50%, respectively, are obtained. For softwoods, the Kappa indices and typical returns are 25-30 and 44. - 48%, respectively (Shackford, L.; A Comparison of Pulping and Bleaching of Kraft Softwood and Eucalyptus Pulps, 36th International Pulp and Paper Congress and Exhibition, October 2003, São Paulo, Brazil).

[0009] The differences in the cooking processes of resinous and hardwood species are addressed by Baptista (Baptista, Cecília de Melo Correia; Influence of cooking conditions on lignin structure and bleachability of Pinus pinaster kraft pulp, University of Beira Interior, Master's Thesis, 2007), having studied the Kraft cooking process of Pinus pinaster at a plateau temperature of 170 °C. As the document explains, lignin dissolution occurs in three distinct phases: the initial phase, the main phase, and the residual phase. The initial delignification phase, slow and controlled by the diffusion of liquor and reaction products, occurs with an increase in the H factor up to values ​​of 100, which corresponds to a delignification of around 25%. The following, main phase, is characterized by an acceleration of delignification and is controlled by chemical reactions. The delignification process progresses until 90% of the area is reached. Petition 870240022363, dated 03 / 15 / 2024, p. 11 / 40 5 / 33 delignification with an H-factor of 1400, and then entering the final, slow, residual delignification phase, where 95% delignification is achieved with an H-factor of 5000, reaching a Kappa index of 22.

[0010] When comparing these results with the Kraft delignification process of Eucalyptus globulus, namely the delignification curves of each species, it is possible to verify that under typical laboratory cooking conditions of E. globulus to achieve a Kappa index of 18, involving an H factor of 480, a temperature of 160 °C and an alkaline load of 17%, the cooking of Pinus pinaster is still at the beginning of the main delignification phase, with 60-70% delignification and a Kappa index of 100.

[0011] The dissolution of lignin during Kraft cooking does not occur uniformly. The cooking liquor initially penetrates the fibers through the lumen and diffuses transversely through the cell wall until it reaches the middle lamella and cell corners. Delignification begins to occur in the secondary cell wall, in the initial phase of cooking, controlled by diffusion. The porosity created by the dissolution of part of the lignin and hemicelluloses in the cell wall allows the liquor to reach the middle lamella and initiate the main phase of delignification. With the partial dissolution of the lignin in the middle lamella, the three-dimensional structure of the wood begins to disintegrate and the fibers to separate. In hardwoods, the lignin in the secondary cell wall is more reactive than in softwoods and, consequently, the Petition 870240022363, dated 03 / 15 / 2024, page 12 / 40 6 / 33 fiber separation point, is reached more quickly (Saka, SR; Thomas, J.; Gratzl, JS; Abson, D., Topochemistry of Delignification in Douglasfir Wood with Soda, Soda-Anthraquinone and Kraft Pulping as Determined by SEM-EDXA*, Wood Science and Technology, 16, 139 — 153, 1982).

[0012] For the reasons described above, the mixed cooking of softwoods and hardwoods raises additional challenges from the point of view of process and final pulp quality. To achieve a given Kappa Index with a mixture of softwoods and hardwoods, there is (i) overcooking of the hardwood, if process conditions closer to those of softwoods are used, or (ii) undercooking of the softwood, if process conditions more suitable for hardwoods are used. Thus, and since undercooking of the softwood leads to partial non-separation of the fibers in the final pulp, industrially practiced mixed cooking typically involves softwoods as the dominant wood, with a smaller percentage of hardwoods, using cooking conditions typical of softwoods.Despite being overcooked, hardwood, due to its richer cellulose content and under appropriate cooking conditions, can contribute favorably to the final pulp production yield and reduce volumetric wood consumption (m3 of wood / Ton of pulp) in the process.

[0013] With cooking conditions adjusted to softwood, Oliveira et al. (Oliveira, RC; Foelkel, CEB; Gomide, JL; Kraft pulp production a Petition 870240022363, dated 03 / 15 / 2024, page 13 / 40 7 / 33 of mixtures of wood from Pinus strobus var. chiapensis and Eucalyptus urophylla, of hybrid origin, Revista Árvore, 3(2), 195 - 207, 1979) carried out Kraft cooking studies of mixtures of wood chips from Pinus strobus var. chiapensis and hybrid Eucalyptus urophylla. They found that pine wood is more difficult to delignify than eucalyptus, thus requiring more drastic cooking conditions. Pine wood, due to its lower density and lower yield, when added in a mixture with predominant eucalyptus (mixture with 33% pine), results in a higher volumetric consumption of wood per ton of final product. There is also a decrease in the refined yield (for example, for an H factor of 1100, there is a yield of 49% with eucalyptus and 46% with 33% pine mixed with eucalyptus) and an increase in the Kappa Index (21 with eucalyptus and 33 with 33% pine mixed with eucalyptus).In turn, the results from these authors show that the addition of 33% eucalyptus mixed with pine does not result in a significant change in the refined yield, whose recorded value was approximately 42-43%. However, for an H-factor of 1100, the Kappa index value decreases from 42 to 33 with the addition of % eucalyptus to the pine. The study does not characterize the mechanical properties of the resulting pastes.

[0014] In 1984, Maddern and co-authors (Maddern, kn; Brumby, PM; Mulcahy, JP, Pulping Alkaline of Hardwood and Softwood Mixtures, Appita, 37 (9), 723-728, 1984) found that the cooking yield Petition 870240022363, dated 03 / 15 / 2024, p. 14 / 40 The yield of 8 / 33 of mixtures of softwoods and hardwoods is lower than the equivalent yield from cooking individual species, namely hardwood. Low softwood incorporation results in a lower total yield due to overcooking of the hardwood. The incorporation of 25% pine in a mixture with eucalyptus leads to a decrease in yield to 45% compared to the yield obtained from cooking eucalyptus alone, 47%. The Kappa index increases from 18 to 21. The alkaline charges for the mixed cooking are also higher compared to those of the individual cooking. Mechanical properties of the resulting pulps are not shown in this work by Madderm and co-authors.

[0015] Gulsoy et al. (Gulsoy, SK; Tufek, S., Effect of Chip Mixing Ratio of Pinus pinaster and Populus tremula on Kraft Pulp and Paper Properties, Ind. Eng. Chem. Res. 52, 6, 2304-2308, 2013) studied mixtures of pine (softwood) and poplar (hardwood) regarding their behavior when subjected to Kraft cooking, with cooking conditions suitable for softwood. The authors found that incorporating hardwood into softwood allows for an increase in the total yield obtained (yield of 49% and a Kappa Index of 49 with the addition of 25% poplar versus a yield of 47 ... with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of 47% with the addition of 25% poplar versus a yield of A Kappa index of 60 (with only pine) and the obtaining of a pulp that is easier to refine. In turn, the incorporation of 25% pine results in a total yield of 52% and a Kappa index of 23 compared to Petition 870240022363, dated 03 / 15 / 2024, page 15 / 40 9 / 33 a total yield of 54% and a Kappa index of 13 with the cooking of only poplar. The authors also verified that for high incorporations of pine, pulps with high viscosity and reject content are obtained. Additionally, a reduction in the mechanical properties of the obtained pulp was shown, with respect to tear resistance, bursting and tensile index, by adding hardwood to the predominant softwood mixture. This decrease is clearly more noticeable than the increase in the values ​​of these properties by adding softwood to the predominant hardwood mixture.

[0016] Bassa et al. (Bassa, Ana Gabriela; Silva, Marcelo; Bassa, Alexandre; Sacon, Vera; Schmidt, Flavia; Silva, Francides, Mixed Brazilian Eucalyptus and Pinus species - Bleaching evaluation, TAPPI Engineering, Pulping and Environmental Conference, 36, 2008) also recovered some of the work from the 1970s on cooking mixtures of conifers and hardwoods. In In 1979, Chen and co-authors (Chen, R.; Garceau, JJ; Kokta, BV Hardwood mixed with softwoods in Kraft pulping, Tappi, Atlanta, 61(7), 35-38, 1978) studied the cooking of mixtures of Populus tremuloides (trembling poplar) and Picea glauca (Canadian pine). They found that adding poplar (a hardwood) to pine (a softwood) in the cooking process resulted in an increase in yield of up to 4%, less waste generation, and better delignification. Petition 870240022363, dated 03 / 15 / 2024, p. 16 / 40 10 / 33

[0017] A work also from the 70s, by Hunt and Hatton (Hunt, K. and Hatton, JV, Increased pulp production by use of hardwoods in softwood kraft mills (1976), Aspen Bibliography, Paper 5001) showed that adding hardwoods to softwoods for cooking is advantageous. They found that higher yields are obtained with softwood mixtures containing up to 20% hardwood than when softwoods are cooked individually, without diminishing strength properties. Less refining energy is required for the resulting pulps.

[0018] Zanão and co-authors studied the Kraft cooking of eucalyptus and pine mixtures with the addition of polysulfides and for a target Kappa Index of 19. The increase in yield obtained (in the order of 1.0 - 2.2%) was attributed to the polysulfides.

[0019] Kraft cooking, as previously mentioned, is generally conducted to obtain chemical pulps with low Kappa indices (on the order of 15-30) and yields of 45-55%. Several studies and industrial practices have aimed to increase cooking yield by interrupting delignification (higher Kappa indices). This is a common practice in pulp production in Sweden. The separation of fibers, not having occurred completely through reaction and dissolution of lignin, is complemented by mechanical defibration, at the exit of the digester, of the partially delignified shavings (Ek, Monica; Gellerstedt, Goran; Henriksson, Gunnar, Pulp and Paper Chemistry and Petition 870240022363, dated 03 / 15 / 2024, page 17 / 40 11 / 33 Technology, Volume 2, Pulping Chemistry and Technology, 2009, De Gruyter, Berlin). However, these practices essentially involve single species.

[0020] Another possibility for increasing the yield of wood cooking is described in patent document US10060075B2, which discloses a cooking method that allows for high yield through Kraft cooking until a Kappa Index value of not less than 30 is obtained, and a reject stream and an accept stream. The reject stream is then subjected to mechanical processes in the presence of bleaching agents such as elemental chlorine, chlorine dioxide, ozone, and hypochlorite before being combined with the accept stream. Additionally, the described Kraft cooking process also involves the use of chemical additives such as anthraquinone and polysulfides. However, the application of the technology to mixtures of softwoods and hardwoods is not exemplified.

[0021] US patent application 3827934A, dated 1971, discloses the obtaining of a high-yield (55-80%) hardwood pulp with a Kappa index of at least 50, wherein the pulp is obtained by a method involving a modification of the normal chemical process, through a cooking process using a lower alkaline charge (an effective alkaline concentration between 6 and 15%) and less severe temperature conditions, between 110 and 154 °C. The pulps obtained by this chemical process are then subjected to mechanical treatment with a counter-current double-disc rotary refiner. Petition 870240022363, dated 03 / 15 / 2024, page 18 / 40 12 / 33

[0022] Hart's work (Hart, P., Production of High Yield Bleached Hardwood Kraft Pulp: Breaking the Kraft Pulp Yield Barrier, Tappi Journal, 10(9), 2011) also uses a similar method: for cooking hardwoods and to increase the yield of the Kraft process (up to 65%, and Kappa Index up to 60), in order to reduce wood consumption and operating costs, a lower effective alkaline charge is used. A higher content of rejects is observed at the digester outlet. These rejects are subsequently reduced by mechanical action.

[0023] US patent application 4869783A, 1986, describes a Kraft cooking process that exhibits higher yield values ​​than are characteristic of chemical processes, involving a first pre-defibration, in which wood chips are subjected to a combination of compression and torsion forces for partial fiber separation, followed by chemical treatment at high temperatures and pressures to obtain Kappa indices of about 45 to 70. The pulp is then delignified with chlorine, chlorine dioxide, or a mixture of both, lowering the Kappa index to values ​​of 15 to 25.

[0024] One alternative to increase the yield of Kraft pulp cooking involves applying a longer impregnation step to the wood, as described by de Souza et al. (de Souza, B.; Gustavo, B.; Colodette, JL; Gomes, FJ Borges; Carvalho, DC, Enhancement of eucalypt pulp yield through extended impregnation cooking; Nordic Pulp & Petição 870240022363, de 15 / 03 / 2024, pág. 19 / 40 13 / 33 Paper Research Journal 2018, 33(2), 175-185). Wedin e co-autores (Wedin, H.; Lindstrom M.; Ragnar, M. , From simple theory to industrial application - extended impregnation kraft cooking, 5th International The Colloquium on Eucalyptus Pulp (ICEP), May 9-12, 2011, Porto Seguro, Brazil, also considered this approach, combining a longer impregnation time with a lower cooking temperature to obtain a higher Kappa Index, up to approximately 28. The increased impregnation time also allowed for a reduction in reject content. Tavast and co-authors (Tavast, D.; Brannvall, E., Increased pulp yield by prolonged impregnation in softwood kraft pulping, Nordic Pulp & Paper Research Journal, 32(1), 2017) also studied the application of increased impregnation time in softwood cooking. It was also found that this increased impregnation time and, additionally, the decrease in the impregnation phase temperature allows for easier fiber separation at high Kappa Indices and a reduction in the reject content obtained. Finally, in 2011, Hart and Colson (Hart, P.; Colson, G.; Antonsson S.; Hjort A., Impact of impregnation on high kappa number hardwood pulps, BioResources, 6(4), 2011) also verified the impact of increasing the time and decreasing the temperature of the impregnation phase on the cooking of hardwood mixtures. It is verified that increasing the impregnation time results in easier fiber separation, even for high Kappa Indices, as well as a reduction in reject content. The cooking described is interrupted to obtain Kappa Indices. Petition 870240022363, dated 03 / 15 / 2024, page 20 / 40 14 / 33 and high levels of rejects. These are defibrated in a high-consistency refiner.

[0025] This highlights the need for a Kraft pulp production process that exhibits high yield and overcomes the aforementioned technological difficulties and challenges of mixed cooking. There is also a need to obtain improved pulps that yield paper products with enhanced paper properties, such as mechanical strength properties. Summary of the invention

[0026] The present invention relates to a process for producing Kraft pulp from mixtures of softwood and hardwood which includes the following steps: a) selection of a mixture of hardwood and softwood chips in a minimum proportion of 51% by mass of hardwood; b) impregnation with a cooking liquor, increasing the temperature between 0.5 and 1.5 °C / min until a cooking temperature is reached; c) cooking the mixture resulting from step b) in a pressurized reactor; d) stopping the cooking process when at least 30% of the lignin has been removed from the softwood; e) decompression and discharge of the reactor; f) separation of the cooking liquor from the partially delignified wood resulting from step d); Petition 870240022363, dated 03 / 15 / 2024, p. 21 / 40 15 / 33 g) mechanical defibration of the wood resulting from step f) until a homogeneous pulp suspension is obtained.

[0027] In a preferred embodiment of the invention, a mixture of hardwood and softwood chips is selected in step a) in a proportion of 85% by mass of hardwood.

[0028] In a preferred embodiment of the invention, the impregnation in step b) is carried out with cooking liquor having an active alkalinity per weight of wood of 0.150 - 0.200 gNa2O / g dry base wood and a sulfide index of 28 - 32%.

[0029] In a preferred embodiment of the invention, the impregnation in step b) is carried out with a liquor volume to wood mass ratio of 3 - 8 L / kg.

[0030] In a preferred embodiment of the invention, the cooking in step c) is carried out at a cooking temperature of 140 to 160 °C.

[0031] In a preferred embodiment of the invention, the interruption of the cooking process in step d) is carried out when between 30% and 60% of the lignin has been removed from the softwood.

[0032] In a preferred embodiment of the invention, the process further includes a drying step of the paste after step g).

[0033] In a preferred embodiment of the invention, the hardwood is eucalyptus wood.

[0034] In a preferred embodiment of the invention, the resinous wood is pine wood. Petition 870240022363, dated 03 / 15 / 2024, p. 22 / 40 16 / 33

[0035] The present invention also relates to paper products characterized by including Kraft pulp obtained by the process described.

[0036] In a preferred embodiment of the invention, the paper product is a corrugated cardboard (containerboard), a kraftliner, a testliner, a fluting paper, a bag paper (sack kraft), a shopping bag paper, a flexible packaging paper, a tissue paper and a printing and writing paper.

[0037] The present invention also relates to a process for producing paper products incorporating Kraft pulp produced by the process described in this invention and which includes the following steps: a) Formation of a suspension of Kraft pulp fibers in a paper machine; b) removal of water from the suspension; c) drying and forming of the paper material.

[0038] In a preferred embodiment of the invention, the process further includes a prior step of disintegrating the Kraft pulp in its dry form before step a). Brief description of the figures

[0039] Figure 1. Kinetic delignification curves of the individual species E. globulus (♦) and P. pinaster () and of mixtures E. globulus / P. pinaster 85 / 15 ( △ ), 70 / 30 (O) and 95 / 5 (O) . IEg — initial delignification phase for cooking E. globulus; IIEg Petition 870240022363, dated 03 / 15 / 2024, page 23 / 40 17 / 33 main delignification phase for cooking E. globulus; IPp - initial delignification phase for cooking P. pinaster; IIPp - main delignification phase for cooking P. pinaster. Detailed description of the invention

[0040] A process for producing Kraft pulp is described herein, using a mixture of hardwood and softwood, in which the former predominates over the latter, with cooking conditions typical of hardwoods, as described in this patent application and claim 1, which, surprisingly, allows obtaining simultaneously a high-yield Kraft pulp (> 60%) with increased mechanical properties compared to pulp produced from 100% hardwood.

[0041] Additionally, the pulp of the invention can be produced on an industrial Kraft pulp production line, normally used for the production of raw pulps with yields of 45-55%.

[0042] The process described in this invention includes a selection of hardwood and softwood chips, with broadleaf wood in a greater proportion. This is followed by impregnation and slow heating (0.5 to 1.5 °C / min) of the mixture with cooking liquor until the cooking temperature is reached. The cooking of the chip mixture then takes place, which can occur in a pressurized reactor, continuously or in batch form. Cooking is stopped when at least 30% of the lignin has been removed from the softwood. Decompression and discharge of the reactor then occur sequentially. Petition 870240022363, dated 03 / 15 / 2024, p. 24 / 40 18 / 33 where the cooking and separation of the black liquor from the resulting wood took place. This is finally defibrated by mechanical means until a homogeneous paste suspension is obtained.

[0043] The cooking interruption point is one of the innovative aspects, along with the other technical characteristics, of this process, as it allows maximizing the pulp production yield. In the present invention, softwood, which is more difficult to delignify, was taken as a reference. This optimal cooking interruption point corresponds to the point at which the cooking liquor has completely diffused through the cell wall of the softwood fibers and reached the middle lamella and cell corners, where there is the highest concentration of lignin in the wood structure. At this point, which occurs at the beginning of the main delignification phase, fiber separation is promoted. In softwood, this point is reached for a higher IK than in the case of hardwood (Lindstrom, 2011).In softwoods, due to their chemical nature (higher lignin content and lower reactivity), there is less depolymerization and lignin dissolution before fiber separation than in hardwoods. At this point, it was found that softwood chips are completely impregnated, with up to 60% of the lignin already removed, and the subsequent mechanical fiber separation process is facilitated, resulting in a low reject content (in the 85 / 15 mixture between 0.7 and 2.5%). At this point, the hardwood chips are already in a phase of... Petition 870240022363, dated 03 / 15 / 2024, page 25 / 40 19 / 33 more advanced delignification, with mechanical separation of its fibers being even easier than for the resinous tree.

[0044] Figure 1 translates these results by the delignification kinetic curves of individual species and mixtures as detailed below.

[0045] Kraft refers to Kraft cooking, or sulfate cooking. This chemical process consists of cooking wood in a cooking liquor usually made up of sodium hydroxide and sodium sulfide, at temperatures of around 140 to 180 °C, in pressurized reactors.

[0046] In the context of the present invention, Kraft pulp refers to pulp obtained by Kraft cooking.

[0047] In the context of the present invention, high yield corresponds to yields > 60% in the context of a Kraft cooking chemical process.

[0048] Within the scope of the present invention, a partially delignified pulp corresponds to a material resulting from cooking interrupted at a stage prior to the residual stage, normally indicated as the end of cooking for obtaining Kraft pulps.

[0049] Within the scope of the present invention, the cooking yield is calculated using the following formula: wood pulp / mass x 100 (weights on a completely dry basis)

[0050] Within the scope of the present invention, the Kappa Index of cooking is calculated using the following formula: (volume of sodium thiosulfate solution used in the blank test - volume of sodium thiosulfate solution) Petition 870240022363, dated 03 / 15 / 2024, p. 26 / 40 20 / 33 sodium consumed in the test with pulp) x concentration of sodium thiosulfate solution * correction factor / (0.1 x mass of completely dry pulp)

[0051] Within the scope of the present invention, the H factor is a cooking variable that combines temperature and time into a single variable and indicates the severity of the cooking.

[0052] Within the scope of the present invention, a cooking liquor corresponds to an aqueous solution consisting of sodium hydroxide (NaOH) and sodium sulfide (Na2S) or to another solution that provides the same technical cooking effect.

[0053] The sulfide index consists of the percentage of sodium sulfide relative to the active alkalinity (sum of the concentration of sodium hydroxide and half the concentration of sodium sulfide) of a cooking liquor.

[0054] Within the scope of the present invention, tissue paper corresponds to papers used for hygienic and sanitary purposes, whether in a domestic environment or in public places.

[0055] Within the scope of the present invention, corrugated paper (containerboard) corresponds to the paper commonly used to make cards (corrugated boards).

[0056] The top and bottom layers of a card (corrugated board) are called linerboard. It is usually a two-layer product, a top layer and a bottom layer. Virgin fiber and recycled fiber are used in the production of this type of paper. In the first option, when the fiber used is predominantly virgin fiber. Petition 870240022363, dated 03 / 15 / 2024, p. 27 / 40 21 / 33 produced chemically by the Kraft method, the product is called kraftliner. When recycled fibers are predominantly used, the product is referred to as testliner. The groove between two liners is called fluting paper (or corrugated medium).

[0057] Within the scope of the present invention, delignification during cooking is calculated using the following formula: Lignin in pulp x yield / lignin wood x 100 Examples Example 1 Cooking stage Details of the procedure

[0058] Mixtures of E. globulus and P. pinaster wood were cooked in an MK digester with white liquor under the conditions detailed in the following section, after analysis of the white liquor (TAPPI - White Liquor ABC Test). After cooking, the partially delignified wood was separated from the black liquor (placed in a fine cloth bag), washed with fresh water until a conductivity of less than 100 mS / m² was achieved, and centrifuged, thus allowing the determination of the total yield. The black liquor was collected and subsequently analyzed for residual alkaline charge (TAPPI T 625 cm⁻¹⁴, Sodium and Sulfate Ion Refrigerant Analysis), residual sulfide (SCAN-N 31:94), concentration of white, green, and black hydrogen sulfate ions (revised 1994), density, pH, and total non-volatile solids content (oven determination). Petition 870240022363, dated 03 / 15 / 2024, p. 28 / 40 22 / 33 105 °C based on the Standard Methods for the examination of water and wastewater, 20th Edition, 254 a 2-58), ash (@ 525°C), calorific value (lower and upper, following the standard E711-81, Standard Test Method for gross calorific value of refuse-derived fuel by the bomb calorimeter).

[0059] Partially delignified wood was defibrated in a VA-type defibrator (a refiner normally used in the production of mechanical pulps). The applied force was 150 kPa, with a disc spacing of 2 mm*. Defibration was carried out using a continuous water stream at the inlet along with the material to be defibrated. The defibrated material (pulp + rejects) was collected in a cloth bag and subsequently centrifuged. Finally, the material obtained was sieved to separate the pulp from the rejects and to determine the purged yield, rejects content, and Kappa index (ISO 302:2004, Pulps - determination of Kappa number).

[0060] After determining the Kappa Index of the raw pulp obtained, the pulp was refined in the PFI refiner (ISO 52642), the shopper degree (°SR) was determined (ISO 5267 / 1) and laboratory sheets (ISO 5269-1:2005, Pulps — Preparation of laboratory sheets for physical testing — Part 1: Conventional sheet-former method) with a basis weight of 135 gseca / m2 were prepared for evaluation of paper properties. Details of cooking conditions

[0061] Based on the tests performed for 100% E. globulus, the following parameters were kept constant in the Kraft cooking process (MK digester): the load Petition 870240022363, dated 03 / 15 / 2024, pp. 29 / 40 23 / 33 alkaline (Active Alkali (in the form of Na2O) / Weight of Wood = 17%), sulfide index (SI = 28%), activity (90%), hydromodulus (4 Liters of White Liquor / Kg of Wood), maximum cooking temperature (160°C), heating time to maximum temperature (140 min).

[0062] Cooking was carried out with mixtures (E. globulus / P. pinaster) 85 / 15 and assessments made of the impact of P. pinaster on paper properties.

[0063] Table 1. Mixture cooking methods performed and their conditions. # Cooking 3 4 5 85 / 15 85 / 15 85 / 15 T max 160 °C Same H-factor as 2 T max 160 °C Time at T max less than 3 T max 160 °C Time at T max between 3 and 4 Maximum cooking temperature (°C) 160 160 160 Time at T max (min) 33 15 21 Total time (min) 171 153 159 H-factor (heating + plateau) 290 174 210 Initial temperature (°C) 26.4 25.2 27.3 Heating time to T max. (min) 138 138 138 Decompression time up to 90 °C, opening (min) 12 12 12 H-factor (heating + plateau + decompression) 300 184 222 Petition 870240022363, dated 03 / 15 / 2024, pp. 30 / 40 24 / 33 Kappa Index (IK) 47 69 59 Evaluation of the cooking stage

[0064] For the 85 / 15 mixture cookings where it was possible to reach the target IK of 50, 60 and 70, a range of purified yields of 62 - 70% and reject content of 0.7 - 2.3% were obtained. These pulp yield results are slightly lower than those obtained in the 100% E. globulus cookings, for the same IK (table 2).

[0065] The incorporation of 15% by mass of P. wood. pinaster promoted an increase in specific wood consumption in the range of 2.38 - 2.65 m3 / ton ad, compared to those obtained for 100% E. globulus (2.20 - 2.31 m3 / ton ad), related to the apparent density of each species and its respective refined yield.

[0066] Table 2. Results of the cooking stage. Wood 85 / 15 E. globulus / P. pinaster 100% E. globulus (Reference) Basic wood density (kg / m3) 543 567 Cooking conditions Kraft AA / PM** (g ​​Na2O / g dry base wood) 0.170 0.170 0.170 0.170 0.170 0.170 IS (%) 28 28 28 28 28 28 Hydromodulus (L / kg) 4.0 4.0 4.0 4.0 4.0 4.0 H-factor (heating + plateau) 290 210 174 191 177 125 H-factor (heating + plateau + decompression) 300 222 184 215 185 141 T max. (oC) 160 160 160 160 160 160 Time at T max (min) 33 21 15 18 20 8 Total time (min) 171 159 153 153 155 143 IK 50 60 70 50 60 70 Petition 870240022363, dated 03 / 15 / 2024, pages 31 / 40 25 / 33 Refined yield (% m / mm wood) 62.6 65.6 6 9.6 68.7 72.9 72.2 Rejects content (% m / mm wood) 0.7 1.0 2.3 0.4 0.8 0.9 CEM*** (m3 / ton a.d.*) 2.65 2.53 2.38 2.31 2.18 2.20 Mixture delignification (%) 79.6 75.7 73.6 80.9 75.9 68.8 * ad - air dry * AA / PM - Active Alkali / Wood Weight * CEM - Specific Wood Consumption Evaluation of papermaking properties

[0067] The papermaking properties of raw pulps with IK 50, 60 and 70 were evaluated. For this purpose, sheets with a basis weight of 135 gDry / m2 were prepared, with an isotropic fiber distribution structure and tested according to standardized methodologies described in Table 3. Sheets were also prepared and evaluated after refining the raw pulp in the PFI refiner (ISO 5264-2) at 1500 and 3000 revolutions.

[0068] Table 3. Physical, optical and structural tests and corresponding standards. Opacity, % Drainage, °SR Grammage, g / m2 Density, kg / m3; Hand index, m3 / kg; Bursting index, kPa.m2 / g; Tensile index, Nm / g; Tear index, mN.m2 / g; Gurley air resistance, (100 ml) / s; Internal bonds (Scott-bonds), J / m2; Bendtsen air roughness, ml / min ISO 2470 ISO 5267 / 1 ISO 5270 NP EN 20534 NP EN 20534 NP 687 ISO 1924 / 2 NP EN 21974 ISO 5636 / 5 TAPPI UM 403 ISO 8791 Petition 870240022363, dated 03 / 15 / 2024, pp. 32 / 40 26 / 33

[0069] Table 4 presents the overall results of the effect of incorporating 15% by mass of P. pinaster on the papermaking properties of Kraftliner paper, with improvements for this type of paper expected to be in strength properties, namely bursting, tensile and tear indices.

[0070] Table 4. Results of the paper evaluation. Madeira 85 / 15 E. globulus / P. pinaster 100% E. globulus (Reference) IK 50 60 70 50 60 70 Refining type (revolutions or time) PFI* PFI* PFI* Valley (27 min) Valley (28 min) Valley (28 min) Drainability (°SR) 29 29 29 29 29 29 Grammage (g / m2) 145.8 146.8 147.8 143.4 148.1 148.9 Thickness (pm) 195 190 195 199 203 216 Bulk (cm3 / g) 1.32 1.30 1.32 1.39 1.37 1.45 Bursting Index (kPa.m2 / g) 5.7 6.1 5.9 5.5 5.5 4.5 Tensile Strength (kN.m / Kg) 83.7 86.6 82.6 80.4 83.2 70.5 Tear Strength (mN.m² / g) 11.6 10.7 10.7 10.8 9.1 8.2 Elongation (%) 3.6 3.7 3.5 2.8 2.9 2.8 TEA Index** (J / g) 2.0 1.8 2.0 1.5 1.6 1.3 Tensile stiffness (kN / m) 2222 2186 2117 2330 2401 2423 Opacity (%) 100.1 99.9 99.8 99.9 99.7 99.8 Capillarity (mm / (10 min)) 39 35 32 45 39 38 Gurley air resistance (s / (100mL)) 59 74 58 36 41 36 Bendtsen roughness (mL / min) 144 128 127 169 142 320 Bendtsen air permeability (mL / min) 542 409 541 433 342 462 Internal connections (Scott-bond) (J / m2) 439 472 415 350 357 335. *Interpolated values ​​for °SR = 29 ** TEA - tensile energy absorption Absorption Petition 870240022363, dated 03 / 15 / 2024, pp. 33 / 40 27 / 33

[0071] A comparative analysis of the structural and strength properties of the 85 / 15 blend pulp (values ​​interpolated to °SR 29) was carried out, evaluating the results for different IK values ​​(50, 60 and 70), compared to 100% E. globulus pulps for the same IK values. It was concluded that the incorporation of 15% by mass of P. pinaster promoted an improvement in strength properties, with an increase in the tear index (7% for IK 50, 18% for IK 60 and 27% for IK 70), an increase in the burst index (4% for IK 50, 11% for IK 60 and 31% for IK 70), and an increase in the tensile index (4% for IK 50, 4% for IK 60 and 70). IK 60 and 17% for IK 70), an increase in internal connections (25% for IK 50, 32% for IK 60 and 24% for IK 70) and an increase in elongation (29% for IK 50, 28% for IK 60 and 25% for IK 70). Example 2

[0072] Cooking was carried out with mixtures (E. (globulus / P. pinaster) 90 / 10 with the cooking steps as described in Example 1. A refined yield of over 60% was obtained. There was also an improvement in strength properties such as tear index, burst index, tensile index, internal bonds and elongation.

[0073] Table 5. Results of the cooking stage. Madeira 90 / 10 E. globulus / P. pinaster Kraft cooking conditions H-factor (heating + plateau) 129 Petition 870240022363, dated 03 / 15 / 2024, pages 34 / 40 28 / 33 Factor H (heating + plateau + decompression) 139 T max. (oC) 160 Time at T max (min) 9 Total time (min) 147 IK 88 Refined yield (% m / mm wood) 69.3 Waste content (% m / mm wood) 1.2 Example 3 Details of cooking conditions

[0074] Cooking was carried out with mixtures (E. Pseudomonas globulus / Pseudomonas pinaster) in the proportions 95 / 5 and 70 / 30 with the cooking steps and conditions as described in Example 1.

[0075] Table 6 shows the cooking conditions for the 95 / 5 mixture.

[0076] Table 6. Mixture cooking methods performed and their respective conditions. # Cooking 3 4 5 95 / 5 95 / 5 95 / 5 Maximum cooking temperature (°C) 160 160 160 Time to T max (min) 23 16 8 Total time (min) 161 154 146 H-factor (heating + plateau) 230 175 128 Initial temperature (°C) 32.0 24.3 30.4 Heating time to T max. (min) 138 138 138 Decompression time and to 90 °C, opening (min) 10 11 10 H-factor (heating + plateau + decompression) 240 183 138 IK 47 66 75

[0077] Table 7 shows the cooking conditions for the 70 / 30 mixture. Petition 870240022363, dated 03 / 15 / 2024, pages 35 / 40 29 / 33

[0078] Table 7. Mixture cooking methods performed and their respective conditions. # Cooking 3 4 5 70 / 30 70 / 30 70 / 30 Maximum cooking temperature (°C) 160 160 160 Time to T max (min) 47 34 23 Total time (min) 185 172 161 H-factor (heating + plateau) 390 305 230 Initial temperature (°C) 31.1 29.4 29.2 Heating time to T max (min) 138 138 138 Decompression time and time to 90 °C, opening (min) 16 10 10 H-factor (heating + plateau + decompression) 400 315 239 IK 53 65 70

[0079] For all tests, refined yields greater than 60% were obtained and an increase in the tear index, burst index, tensile index, internal bonds and elongation properties was obtained, in line with those verified in the previous examples, and as described below. Evaluation of the cooking stage

[0080] For the cooking of the 95 / 5 mixture paste where it was possible to reach the target IK of 50, 60 and 70, a range of purified yields of 68 - 71% and reject content of 0.7 - 1.1% were obtained (Table 8). For the cooking of the 70 / 30 mixture paste where it was possible to reach the target IK of 50, 60 and 70, a range of purified yields of 69 - 70% and reject content of 0.4 - 0.7% were obtained (Table 8).

[0081] Table 8. Results of the cooking stage. Petition 870240022363, dated 03 / 15 / 2024, pages 36 / 40 30 / 33 Wood 95 / 5 E. globulus / P. pinaster 70 / 30 E. globulus / P. pinaster Basic wood density (kg / m3) 559 519 Cooking conditions kraft AA / PM** (g ​​Na2O / g dry base wood) 0.170 0.170 0.170 0.170 0.170 0.170 IS (%) 28 28 28 28 28 28 Hydromodulus (L / kg) 4.0 4.0 4.0 4.0 4.0 4.0 H-factor (heating + plateau) 230 175 128 390 305 230 H-factor (heating + plateau + decompression) 240 183 138 400 315 239 T max. (oC) 160 160 160 160 160 160 Time at T max (min) 23 16 8 47 34 23 Total time (min) 161 154 146 185 172 161 IK 50 60 70 50 60 70 Refined yield (% m / mmwood) 68.1 69.5 71.4 68.8 69.1 69.7 Rejects content (% m / mmwood) 0.7 1.3 1.1 0.4 0.7 0.6 CEM*** (m3 / ton ad *) 2.36 2.32 2.25 2.52 2.51 2.49 Mixture delignification (%) 80.9 71.1 65.6 76.4 73.1 70.2 * ad - air dry ** AA / PM - Active Alkali / Wood Weight *** CEM - Specific Wood Consumption Evaluation of papermaking properties

[0082] Table 9 presents the overall results of the effect of incorporating 5% by mass and 30% by mass. Petition 870240022363, dated 03 / 15 / 2024, pages 37 / 40 31 / 33 P. pinaster wood pulp in cookings for the production of Kraft pulps on paper mills for Kraftliner paper.

[0083] Table 9. Results of the paper evaluation. Wood 95 / 5 E. globulus / P. pinaster 70 / 30 E. globulus / P. pinaster 100 % E. globulus (Reference) IK 50 60 70 50 60 70 50 60 70 Refining type (revolutions or time) PFI PFI PFI PFI PFI PFI Vall ey (27 min) Vall ey (28 min) Vall ey (28 min) Drainability (°SR) 29 29 30 30 29 30 29 29 29 Weight (g / m2) 144 .7 147 .9 145 .2 146 .5 146 .8 145 .8 143.4 148.1 148.9 Thickness (pm) 185 196 196 183 192 195 199 203 216 Bulk (cm3 / g) 1.2 8 1.3 2 1.3 5 1.2 5 1.3 1 1.3 4 1.39 1.37 1.45 Bursting Index (kPa.m2 / g) 6.5 6.0 5.6 7.1 6.8 6.3 5.5 5.5 4.5 Tensile Index (kN.m / Kg) 88.7 82.8 84.8 86.4 91.7 89.7 80.4 83.2 70.5 Tear Index (mN.m2 / g) 10.7 10.6 10.7 11.9 12.5 11.8 10.8 9.1 8.2 Lengthening (%) 3.7 3.7 3.9 4.8 4.2 3.8 2.8 2.9 2.8 TEA Index** (J / g) 2.1 2.1 2.2 2.7 2.6 2.3 1.5 1.6 1.3 Tensile stiffness (kN / m) 208 4 204 5 198 3 182 5 219 4 210 3 2330 2401 2423 Opacity (%) 100.0 99.9 99.9 99.8 99.8 100.0 99.9 99.7 99.8 Capillarity (mm / (10 min)) 30 29 36 26 27 32 45 39 38 Gurley air resistance (s / (100mL)) 45 48 41 86 67 58 36 41 36. Petition 870240022363, dated 03 / 15 / 2024, pp. 38 / 40 32 / 33 Bendtsen Roughness (mL / min) 124 120 153 88 120 115 169 142 320 Bendtsen Air Permeability (mL / min) 363 240 311 151 176 254 433 342 462 Internal Bonds (Scottbond) (J / m2) 466 513 484 579 604 385 350 357 335 ** TEA - Tensile Energy Absorption

[0084] A comparative analysis of the structural and strength papermaking properties of the 95 / 5 and 70 / 30 blend pulps was also carried out, evaluating the results for the different IKs (50, 60 and 70), compared to 100% E. globulus pulps, for the same IKs.

[0085] It was concluded that the incorporation of 5% P. pinaster promoted an improvement in resistance properties, with an increase in the tear index (16% for IK 60 and 30% for IK 70), an increase in the burst index (18% for IK 50, 9% for IK 60 and 24% for IK 70), an increase in the tensile index (10% for IK 50 and 20% for IK 70), an increase in internal bonds (33% for IK 50, 44% for IK 60 and 44% for IK 70) and an increase in elongation (32% for IK 50, 28% for IK 60 and 39% for IK 70).

[0086] It was concluded that the incorporation of 30% P. pinaster promoted an improvement in resistance properties, with an increase in the tear index (10% for IK 50, 37% for IK 60 and 44% for IK 70), an increase in the burst index (29% for IK 50, 24% for IK 60 and 40% for IK 70), an increase in the index Petition 870240022363, dated 03 / 15 / 2024, pp. 39 / 40 33 / 33 tensile strength (7% for IK 50, 10% for IK 60 and 27% for IK 70), an increase in internal bond strength (65% for IK 50, 69% for IK 60 and 15% for IK 70) and an increase in elongation (71% for IK 50, 45% for IK 60 and 36% for IK 70). Petition 870240022363, dated 03 / 15 / 2024, p. 40 / 40

Claims

1 / 2 CLAIMS 1. Kraft pulp production process characterized by comprising the following steps: a) selection of a mixture of hardwood and softwood chips in a minimum proportion of 51% by mass of hardwood; b) impregnation with a cooking liquor by raising the temperature between 0.5 and 1.5 °C / min to a cooking temperature; c) cooking of the mixture resulting from step b) in a pressurized reactor; d) interruption of cooking when at least 30% of the lignin has been removed from the softwood; e) decompression and discharge of the reactor; f) separation of the cooking liquor from the partially delignified wood resulting from step d); g) mechanical defibration of the wood resulting from step f) until a homogeneous pulp suspension is obtained.

2. Process according to the preceding claim characterized in that in step a) a mixture of hardwood and softwood chips is selected in a proportion of 85% by mass of hardwood.

3. Process according to any of the preceding claims characterized in that the impregnation of step b) is carried out with cooking liquor having an active alkalinity per weight of wood of 0.150 - 0.200 gNa20 / g dry wood base and a sulfide index of 28 - 32%.

4. Process according to any of the preceding claims characterized in that the impregnation of step b) is carried out with a liquor volume to wood mass ratio of 3 - 8 L / kg. Petition 870250059598, dated 11 / 07 / 2025, p. 16 / 17 2 / 2 5. Process according to any of the preceding claims characterized in that the cooking of step c) is carried out at a cooking temperature of 140 to 160°C.

6. Process according to any of the preceding claims characterized in that the interruption of the cooking in step d) is carried out when between 30% and 60% of the lignin has been removed from the softwood.

7. Process according to any of the preceding claims characterized by further comprising a drying step of the paste after step g).

8. Process according to any of the preceding claims characterized by, in step (a), eucalyptus wood being selected as hardwood.

9. Process according to any of the preceding claims characterized by, in step a) the pine wood being selected as softwood. Petition 870250059598, dated 11 / 07 / 2025, p. 17 / 17

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