Method for producing cellulose pulp, cellulose pulp, use of cellulose pulp and paper packaging

Abstract

The invention relates to a method for producing cellulose pulp with increased Kappa value, lignin content, strength and stiffness, wherein said method does not include a bleaching step. A cellulose pulp obtained by the method, use thereof and paper packaging obtained from said cellulose pulp are also disclosed.

Description

Pulp Production Process, Pulp Production, Pulp Use and Paper Packaging Field of invention

[0001] The present invention pertains to the field of packaging and relates to an improved process for producing cellulose pulp useful for preparing paper packaging. Said cellulose pulp exhibits stiffness and strength properties, as well as increased Kappa number and lignin content compared to bleached cellulose pulp, and the process of the present invention does not comprise a bleaching step. The invention also relates to the unbleached cellulose pulp obtained by the process, its use, and to paper packaging obtained from said cellulose pulp. Background of the invention

[0002] The quality and final characteristics of a paper product are directly associated with the type of cellulose fiber used in its composition.

[0003] The properties of cellulose pulp can vary depending on the pulping process and the origin of the cellulose fiber, which can be short-fiber wood (hardwood), long-fiber wood (softwood) or both.

[0004] Examples of short-fiber wood species are birch, oak, beech, maple, and eucalyptus; examples of long-fiber wood species are hemlock cedar, spruce, pine, Southern pine, radiata pine, slash pine, Douglas fir, white fir, Scandinavian pine, and Alpine lodgepole fir.

[0005] In recent years, several studies have been carried out with the aim of relating the impact of modifications in the characteristics of cellulose fibers on the physical-mechanical properties of paper products.

[0006] Among these characteristics of cellulose fibers, their lignin content is considered important for the development of paper products with good rigidity and physical resistance characteristics, without compromising their structure.

[0007] In addition to the importance of fiber quality and improving its characteristics to meet marketing objectives, the pulp and paper industry faces constant challenges in solving problems related to the high consumption of industrial water and inputs in its processes, which results in high energy consumption and waste generation, i.e., generating a significant environmental impact.

[0008] Additionally, the bleaching processes described in the state of the art were introduced into the cellulose fiber production process with the aim of achieving a high brightness content (% brightness or % whiteness), but they entail a high consumption of inputs, generating a high financial expense and consequent impact on the production chain.

[0009] Therefore, eliminating the bleaching stage can be a solution to promote a reduction in the consumption of chemical products used in the pulping process and, thus, increase the efficiency of the pulp production process.

[0010] Furthermore, obtaining a paper product that has application in the packaging market, that is, with specific characteristics, such as greater rigidity, requires a process that is different from those described in the art, as these aim to achieve a high degree of delignification, which would compromise the rigidity of the pulp obtained.

[0011] This new demand brings a significant challenge in terms of process kinetics, since while it is necessary to defiberize the wood (raw material) to obtain cellulose pulp, a pulp with greater rigidity must maintain a higher lignin content in the cellulose fibers.

[0012] In known pulping processes, it is not possible to have selectivity when cooking the wood to defiberize it, particularly in relation to carbohydrates and lignin.

[0013] Furthermore, it is important to have a certain lignin content present in the resulting cellulose pulp to ensure the stiffness of interest, so a new process is necessary.

[0014] WO2020 / 229737 describes the use of fiber formulations selectively derived from hardwood or softwood. long staple fiber or a combination thereof to manufacture towels, tissue products and other sustainable hygiene products that exhibit greatly improved softness, water absorption capacity and tensile strength compared to bleached fibers.

[0015] Thus, this document teaches about the use of unbleached fibers to obtain paper products with improved physical characteristics compared to the use of bleached fibers, but does not specifically refer to the stiffness and strength of the paper product, being applied to the tissue paper market and not to the packaging market.

[0016] In turn, document CN102061642B describes a method for improving the strength of medium corrugated paper and cardboard using high-yield pulp waste liquor containing hemicellulose and lignin. High-yield pulp is not obtained through a chemical fiber separation process, but rather through a mechanical defibrillation process, so that mechanical fibers have lower tensile and strength values ​​compared to chemical fiber.

[0017] The comparison of paper products obtained from the use of bleached or unbleached fibers is already known in the state of the art. However, the development of a pulping process without the bleaching step is urgently needed to produce a cellulose pulp with a higher lignin content and greater rigidity from short-fiber wood ("hardwood"). The pulping process presents a decrease in the generation of residues, a lower degree of soiling and greater efficiency through the reduction of the inputs used, reducing the carbon footprint and increasing the yield of the process as a whole.

[0018] Furthermore, the global demand for recyclable and low-cost cellulose fibers is also related to the objective of replacing fossil-based products in the market with renewable and biodegradable materials.

[0019] Thus, it is still necessary to develop a cellulose pulp production process that is useful for obtaining a paper product with high stiffness when compared to that product originating from bleached cellulose pulp, in which said cellulose pulp has an increased Kappa value and a higher content of lignin .

[0020] Additionally, the production process of said pulp eliminates the bleaching stage, providing a more efficient process that consumes fewer inputs, reducing process costs and also the generation of waste, thus improving its carbon footprint. Summary of the invention

[0021] The present invention aims to provide a process for producing cellulose pulp with increased Kappa value, lignin content and stiffness, without being subjected to a bleaching step.

[0022] The terms "cellulose pulp of the present invention", "unbleached cellulose pulp", "unbleached cellulose pulp", "unbleached pulp", "unbleached pulp" and "pulp without bleaching step" are interchangeable with each other and should be understood as the cellulose pulp obtained by the unbleached process of the present invention.

[0023] The terms "bleached pulp", "bleached pulp", "reference pulp", "bleached pulp", "bleached pulp" and "bleached reference pulp" are interchangeable and should be understood as pulp obtained by a process comprising a bleaching step.

[0024] A first embodiment of the present invention relates to a process for producing cellulose pulp from cellulosic raw material, without going through a bleaching step and which results in a product with high rigidity and resistance, in which the process comprises the following steps: a) providing a cellulosic raw material; b) subjecting the cellulosic raw material to a chemical treatment, through cooking in a digester; c) carrying out the delignification of the pulp resulting from step (b); d) purifying the pulp from step (c); e) controlling the pH of the pulp from step (d); f) dry the pulp from step (e).

[0025] A second embodiment of the invention relates to cellulose pulp produced from said process, said pulp having increased degree of rigidity and resistance when compared to a cellulose pulp obtained from a pulping process comprising a bleaching step.

[0026] A third embodiment of the invention concerns the use of the cellulose pulp obtained by said process to produce a paper packaging.

[0027] And a fourth embodiment of the present invention relates to a paper packaging produced from the pulp obtained by said process. Brief Description of the Drawings

[0028] Figure 1 presents an illustrative flowchart of the cellulose pulp production process of the present invention.

[0029] Figure 2 illustrates the variation in viscosity of the unbleached cellulose pulp of the present invention in relation to a cellulose pulp obtained from a pulping process comprising a bleaching step.

[0030] Figure 3 illustrates the variation in brightness of the unbleached cellulose pulp of the present invention in relation to a cellulose pulp obtained from a pulping process comprising a bleaching step.

[0031] Figures 4A-4C illustrate the variation in chromatic coordinates (L*a*b) of the unbleached cellulose pulp of the present invention in relation to a cellulose pulp obtained from a pulping process comprising a bleaching step, according to the parameters / scales established by the CIE (Commission Internationale de l'Eclairage).

[0032] Figures 5A-5C illustrate, respectively, the variation in the degree of fiber straightness, Curls index, and Kinks index (indices that measure the degree of curvature and breakage), of the unbleached cellulose pulp of the present invention in relation to a pulp cellulose obtained from a pulping process that includes a bleaching step.

[0033] Figures 6A-6C illustrate the drainability and tensile index characteristics of the cellulose pulps of the present invention (without bleaching) and the reference pulp (with bleaching), both without refining and with increased refining.

[0034] Figures 7A-7C illustrate the burst index characteristics of the cellulose pulps of the present invention (without bleaching) and the reference pulp (with bleaching), both without refining and with increasing refining, and their relationship to the tensile index. Detailed description of the invention

[0035] The present invention relates to a process for producing cellulose pulp useful for preparing paper packaging, wherein said cellulose pulp exhibits increased stiffness and strength properties compared to bleached cellulose pulp. The process of the present invention does not include the bleaching step per se, since there is a significant reduction in the amount of chemical inputs used in delignification and bleaching (soda, peroxide, and chlorine dioxide), and it reduces the generation of solid residues and the degree of soiling in the process, while providing an increase in the Kappa number, lignin content, and overall pulping yield. The process of the present invention is also more environmentally friendly.

[0036] The inventors of the present invention have developed a process that involves new cooking kinetics, which will provide greater selectivity in the delignification of the raw material - wood, preferably short-fiber wood ("hardwood") -, without the generation of agglomerates and / or weak points, ensuring excellent yield and a pulp with the desired degree of rigidity.

[0037] Carbohydrates and lignin have different glass transition temperatures, which means that by changing the cooking kinetics in the state-of-the-art pulping process, it is possible to increase the Kappa number and the lignin content of the resulting pulp.

[0038] Furthermore, it is also possible to increase the overall yield of the pulping process by redistributing the alkaline load and using lower temperatures, ensuring more selective cooking and a low reject content, as well as lower specific wood consumption (SWC) and lower steam consumption in the digester.

[0039] In a preferred embodiment of the present invention, the process comprises the following steps: a) providing a cellulosic raw material; b) subjecting the cellulosic raw material to a chemical treatment, through cooking in a digester; c) carrying out the delignification of the pulp resulting from step (b); d) purifying the pulp from step (c); e) controlling the pH of the pulp from step (d); f) drying the pulp from step (e).

[0040] Preferably, the cellulosic raw material may be a pulp originally from coniferous or hardwoods, more specifically eucalyptus, pine, birch or beech, eucalyptus Kraft pulp or even agro-industrial residues, such as bagasse and sugarcane straw or rice straw or wheat straw, obtained by: Kraft pulping; or sulfite pulping; or steam explosion; or fiber explosion with ammonia; or dilute acid hydrolysis; or alkaline hydrolysis; or oxidative alkaline treatment; or enzymatic treatment; or Organosolv processing. However, there is no limitation on the cellulosic raw material to be provided at the beginning of the process (step a).

[0041] Preferably, chemical pulping is a Kraft-type process.

[0042] The chemical pulping process, more specifically the Kraft pulping process, as already described in the state of the art, comprises treating fibers of plant origin, including the following steps: a) digestion - where the fibers of vegetable origin are cooked together with sodium hydroxide and sodium sulfide to separate the brown cellulose pulp (PM) from the lignin; b) separation of black liquor from cellulose - the black liquor has to be separated from the brown cellulose pulp (PM); c) recovery boiler - the black liquor is treated until it can be burned in the recovery boiler to generate energy; d) closing the circuit by recovering sodium hydroxide, sodium sulfide and water; e) transformation of the brown cellulose pulp (PM) into bleached cellulose (CL); said transformation comprises i) washing the cellulose pulp with water to eliminate the residual black liquor; ii) pre-bleaching; iii) bleaching; iv) drying of the cellulose (CL).

[0043] The inventors observed an increase in the lignin content, stiffness, strength, and Kappa number of the cellulose pulp obtained by the process described herein, without undergoing a bleaching step. The strength properties of cellulose pulp can be measured by several indices known in the prior art, including strength along the z-axis, that is, in the direction perpendicular to the principal plane.

[0044] Figure 1 illustrates the steps of the process of the present invention. The cellulose pulp production process comprises the steps of: a) providing a cellulosic raw material; b) subjecting the cellulosic raw material to a chemical treatment, through a cooking step in a digester, in which - the total alkaline load (% AE - Effective Alkali) is 17-20%; - the Kappa number is increased from the range of 16-19 to the range of 23-30; the distribution of alkaline charge CA AE in the impregnation vessel and the digester is, respectively, 75 / 25; - the temperature in the impregnation vessel, at the top (liquor) and extraction is 130-140°C; - the ITC ("Isothermal Cooking") cooking temperature is 135-140°C; - the temperature at the bottom of the digester is 85-95°C; - the residual alkali load expressed as NaOH is 5.0-9.0 g / L; c) perform delignification of the pulp resulting from step (b), in which: - the Kappa number varies in the range of 23 to 30; - the NaOH and / or oxidized white liquor (OBL) load in reactor 1 (Rl) is 0.0 to 3.0 kg / ton of air-dried cellulose (tsa); - the Rl temperature is 80-90°C and the Rl retention time is 60 min; - Rl pressure is 550-650 Kpa; - the O2 load of Rl is up to 3.0 kg / tsa; d) purify the pulp from step (c), in which the purified pulp yield is approximately 55.0-57.0%; e) maintain the pH of the pulp in the range of 4.5-6.0 by adding sulfuric acid (H2SO4); f) send the purified material with a pH in the range of 4.5-6.0 to a storage tower; g) send the material obtained in the storage tower to a drying machine.

[0045] In one embodiment of the invention, the pulping process is a Kraft pulping process.

[0046] During the cooking process in step b), the Kappa number is migrated from the range of 16-19 to the range of 23-30. The change in the Kappa number is carried out incrementally, by altering the parameters of the cooking, delignification and drying process, until reaching the ideal conditions for a product that does not undergo a bleaching step.

[0047] The Kappa number transition begins in the range of 17- 18 and increased according to the retention time of the cooking reactor until reaching a stable Kappa number in the range of 23-30.

[0048] The distribution of the alkaline load starts at a 40 / 60 ratio in the impregnation vessel and digester, respectively, and is changed by reallocating the load from the digester to the impregnation vessel, i.e., increasing the load in the impregnation vessel until it reaches a 75 / 25 ratio in the impregnation vessel and digester, respectively.

[0049] The increase in residual alkalis is a result of changes made to the process (distribution of alkaline load in the impregnation vessel and digester, and temperature reduction).

[0050] The delignification process in step c) is carried out with oxygen (O2). During the production of cellulose pulp that does not undergo a bleaching step, the Kappa number at the delignification output must be maintained in accordance with the Kappa number fed to the digester and the brightness must be controlled at a value of 42% ISO.

[0051] The oxygen load used in the delignification stage is as low as possible, limited to 3.0 kg / dtsa. If the brightness is <42% ISO, the O2 load should be maintained. If it is >42% ISO, the oxygen load should be reduced to a value that can reach 0.0 kg / dtsa. Reducing the oxygen load increases the output Kappa number and reduces brightness.

[0052] The pH at the end of delignification step c) must be kept <9.5.

[0053] The pH control in step e) is to maintain the pH of the pulp in the range of 4.5-6.0. This control is carried out through a acid treatment, in which sulfuric acid (H2SO4) is added to promote fiber deswelling and aid drainage, so that they can easily pass through the drying machine in step g).

[0054] Preferably, additives are used as drainage aids in the brown wash in order to improve the drainage efficiency and runnability (i.e., productivity with speed) of the drying machine in step g). The additives can be: polymers, preferably polyacrylamides, acrylates and acrylic acids; and mineral fillers, preferably bentonite.

[0055] In a further embodiment of the present invention, a cellulose pulp produced from the production process without a bleaching step of the invention is disclosed, said pulp increasing the degree of stiffness and strength of a cellulose pulp obtained from a pulping process comprising a bleaching step.

[0056] In another embodiment of the present invention, the use of cellulose pulp obtained by the process of the present invention to produce a paper packaging is described.

[0057] In yet another embodiment of the present invention, there is disclosed a paper package produced from cellulose pulp obtained by the process of the present invention. Examples

[0058] The following examples will further illustrate the present invention, and the particular conditions and parameters described represent preferred, but not limiting, embodiments of the present invention. Example 1: Comparison of digester cooking parameters for the cellulose pulp of the present invention compared to a prior art bleached cellulose pulp

[0059] Table 1 below illustrates the comparison of the cooking parameters of the digester of the cellulose pulp obtained through the unbleached process of the present invention in relation to a prior art bleached cellulose pulp. Table 1: Digester cooking parameters Example 2: Comparison of the delignification parameters of the cellulose pulp of the present invention compared to a bleached cellulose pulp of the prior art

[0060] Table 2 below illustrates the comparison of the delignification parameters of the cellulose pulp obtained through the unbleached process of the present invention in relation to a prior art bleached cellulose pulp. Table 2: Pulp delignification parameters Example 3: Physical and chemical properties of cellulose pulp obtained by the unbleached process of the present invention.

[0061] Comparative tests were carried out to evaluate the characteristics of the cellulose pulp obtained from the process of the present invention, with an increase in its rigidity and resistance properties, in addition to a reduction in the consumption of chemical inputs used in delignification and bleaching, the generation of solid waste through the ratio of tons of dry solids per ton of dry cellulose to the art - tss / tsa and the degree of dirtiness of the process, while at the same time providing an increase in the Kappa number, lignin content and pulp yield.

[0062] The cellulose pulp of the present invention has an average viscosity of 1180 dm 3 / kg, representing an increase of 48% compared to a reference cellulose pulp obtained from a pulping process comprising a bleaching step. The increase in viscosity is illustrated in Figure 2.

[0063] The increase in viscosity of cellulose pulp obtained without a bleaching process occurs due to the preservation of carbohydrate chains through less drastic and more selective cooking, in addition to the absence of delignification reactions during bleaching.

[0064] The cellulose pulp of the present invention has an average brightness of 38% ISO, representing a reduction of 58% in relation to to a cellulose pulp obtained from a pulping process that includes a bleaching step. The reduction in the brightness of the cellulose pulp is illustrated in Figure 3.

[0065] The cellulose pulp of the present invention has average chromatic coordinates of L ~ 78, a ~ 2.5 and b ~ 16.4, which represents a shift in the color of the product towards a more reddish (a), yellowish (b) and opaque (L) tone.

[0066] The change in chromatic coordinates is due to the greater retention of chromophore groups from lignin in the chemical structure of the pulp, since it was not subjected to bleaching reactions. The change in chromatic coordinates of the cellulose pulp of the present invention relative to the reference pulp, i.e., a cellulose pulp obtained from a pulping process comprising a bleaching step, is illustrated in Figures 4A-4C.

[0067] Furthermore, the cellulose pulp of the present invention had an average total lignin content of 2.4%, while a cellulose pulp obtained from a pulping process comprising a bleaching step had an average content of 0.1%.

[0068] The difference mentioned above is associated with both the cooking kinetics and the non-performance of the bleaching stage, whose oxidative reactions aim to selectively remove lignin and chromophore groups.

[0069] The greater lignin retention also resulted in obtaining a cellulose pulp with an increased Kappa number in relation to the bleached reference pulp.

[0070] Both the less drastic cooking - which resulted in a cellulose pulp with a higher lignin content, and the presence of agglomerated fibers, resulted in obtaining a pulp with more rigid fibers and less susceptible to twisting and bending.

[0071] The phenomenon mentioned above can be observed in Figures 5A-5C through a 3% increase in the degree of straightness of the fibers and by the reductions of 19% and 15%, respectively, in the Curls and Kinks indices (indices that measure the degree of curvatures and breaks), in relation to to a cellulose pulp obtained from a pulping process that includes a bleaching step.

[0072] The increase in the degree of straightness indicates that the fibers are straighter, which means that these fibers are less chemically and physically attacked, resulting in a lower breakage rate.

[0073] Furthermore, the unrefined PFI cellulose pulp of the present invention (i.e., with 0 PFI revolutions) presented drainability values ​​°SR (Schopper-Riegler) and tensile index 7% lower and 14% higher, respectively, in relation to a reference cellulose pulp comprising a bleaching step.

[0074] However, with the increase in refining energy (increase in the PFI revolutions value), an inversion of the behavior is observed, with the pulp of the present invention (without bleaching) showing increases in the °SR value at the same time as it demonstrated reductions in the traction index in relation to the reference (with bleaching), as illustrated in figures 6A-6C.

[0075] Similar behavior is observed for the burst index in Figure 7A, with the cellulose pulp of the present invention (without bleaching) showing an increase of 4.5% for the unrefined pulp (0 PFI revolutions), but there were reductions of up to 12% for the refined pulps under the same refining energy (i.e., under the same number of PFI revolutions).

[0076] Given the increase in the °SR value for the refined pulps of the present invention (without bleaching), for a pulp with a °SR of 35, a reduction of approximately 20% in the burst index is observed in relation to the reference pulp (with bleaching), as can be seen in Figure 7B.

[0077] The relationship between the burst index and the traction index presents curves with similar behavior for both products (without bleaching and with bleaching), as illustrated in Figure 7C, and to reach a traction index of 60 Nm / g for the pulp of the present invention (without bleaching), a reduction of approximately 10% in the burst index is observed in relation to the reference pulp (with bleaching).

[0078] It is understood that when a parameter range is given, all integers and ranges within that range, and tenths and Hundredths are also provided by the modalities. For example, "5-10%" includes 5%, 6%, 7%, 8%, 9%, and 10%; 5.0%, 5.1%, 5.2%, . . . .9, 8%, 9.9%, and 10.0%; and 5.00%, 5.01%, 5.02%, . . . .9, 98%, 9.99%, and 10.00%; as well as, for example, 6-9%, 5.1%-9.9%, and 5.01%-9.99%. Likewise, when a list is presented, unless otherwise indicated, it should be understood that each individual element of that list and each combination of components of that list is a separate modality. For example, "1, 2, 3, 4 and 5" includes, among numerous modalities, 1; 2; 3; 1 and 2; 3 and 5; 1, 3 and 5; and 1, 2, 4 and 5.

[0079] It should be understood that the embodiments described above are merely illustrative and that various modifications may be made by a person skilled in the art to them without departing from the scope of the present invention. Consequently, the present invention should not be considered limited to the exemplary embodiments described in the present application. Furthermore, the present disclosure may include subject matter not currently claimed but which may be claimed in the future in combination with or separately from the features herein claimed. References

[0080] CORREIA, F. M . , et al "Revisiting kappa number - concepts and applications in the pulp industry", The Paper, vol. 80, no. 07, pp 77-89, July 2019.

Claims

REVENUES 1. Process for producing cellulose pulp from cellulosic raw material without going through a bleaching step, characterized by the fact that the process comprises the following steps: a) supplying a cellulosic raw material; b) subjecting the cellulosic raw material to a chemical treatment, through cooking in a digester; c) carrying out the delignification of the pulp resulting from step (b); d) purifying the pulp from step (c); e) controlling the pH of the pulp from step (d); f) drying the pulp from step (e).

2. Process according to claim 1, characterized in that the cellulosic raw material is a pulp originally from coniferous or hardwood, more specifically from eucalyptus, or pine, or birch or beech, eucalyptus Kraft pulp or even agro-industrial residues, such as bagasse and sugarcane straw or rice straw or wheat straw.

3. Process according to claim 1 or 2, characterized in that the cellulosic raw material comes from Kraft pulping, sulphite pulping, steam explosion, ammonia fibre explosion, dilute acid hydrolysis, alkaline hydrolysis, oxidative alkaline treatment, enzymatic treatment or Organosolv processing.

4. Process according to any one of claims 1 to 3, characterized in that the Kappa number in step (b) is increased from the range of 16 to 19 to the range of 23 to 30.

5. Process according to any one of claims 1 to 4, characterized in that the distribution of alkaline charge in the impregnation vessel and in the digester is, respectively, 75 / 25.

6. Process according to any one of claims 1 to 5, characterized in that the delignification process of step (c) is carried out with oxygen (O2).

7. Process according to any one of claims 1 to 6, characterized in that the pH at the end of delignification step (c) is less than 9.

5.

8. Process according to any one of claims 1 to 7, characterized in that the pH control in step (e) is through an acid treatment.

9. Process according to claim 8, characterized in that the acid treatment is with the addition of sulfuric acid (H2SO4).

10. Process according to claim 9, characterized in that the pH of the pulp from step (e) is maintained in the range of 4.5 to 6.

0.

11. Process according to any one of claims 1 to 10, characterized in that additives are used as drainage aids in step (g).

12. Cellulose pulp characterized by the fact that it is obtained by the process without a bleaching step as defined in any one of claims 1 to 11.

13. Cellulose pulp according to claim 12, characterized in that it has increased rigidity and resistance properties in relation to a bleached cellulose pulp.

14. Use of the cellulose pulp as defined in any one of claims 12 to 13 characterized in that it is to prepare a paper packaging.

15. Paper packaging characterized in that it is produced from cellulose pulp as defined in any one of claims 12 to 13.

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